diff --git a/AGENTS.md b/AGENTS.md
index c6c2517..d7dfd25 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -25,14 +25,17 @@ reichard.io/poiesis/
 ├── internal/
 │   ├── runtime/              # Runtime management, transpilation, execution
 │   │   ├── runtime.go
-│   │   └── runtime_test.go
+│   │   ├── runtime_test.go
+│   │   └── options.go
 │   ├── functions/            # Function registration framework
-│   │   ├── collector.go
 │   │   ├── registry.go
 │   │   ├── types.go
-│   │   ├── typescript.go
 │   │   ├── typescript_test.go
 │   │   └── functions_test.go
+│   ├── tsconvert/            # Go-to-TypeScript type conversion utilities
+│   │   ├── convert.go
+│   │   ├── types.go
+│   │   └── convert_test.go
 │   └── stdlib/               # Standard library implementations
 │       ├── fetch.go
 │       └── fetch_test.go
@@ -40,8 +43,9 @@ reichard.io/poiesis/
 
 ## Key Packages
 
-- `reichard.io/poiesis/internal/runtime` - Runtime management, TypeScript transpilation, JavaScript execution
-- `reichard.io/poiesis/internal/functions` - Generic function registration framework (sync/async wrappers, automatic JS/Go conversion via JSON, type definition generation)
+- `reichard.io/poiesis/internal/runtime` - Runtime management, TypeScript transpilation, JavaScript execution, per-runtime type management
+- `reichard.io/poiesis/internal/functions` - Generic function registration framework (sync/async wrappers, automatic JS/Go conversion via JSON)
+- `reichard.io/poiesis/internal/tsconvert` - Go-to-TypeScript type conversion utilities and type declaration generation
 - `reichard.io/poiesis/internal/stdlib` - Standard library implementations (fetch)
 
 ## Function System
@@ -49,6 +53,7 @@ reichard.io/poiesis/
 ### Registration
 
 Two types of functions:
+
 - **Sync**: `RegisterFunction[T, R](name, fn)` - executes synchronously, returns value
 - **Async**: `RegisterAsyncFunction[T, R](name, fn)` - runs in goroutine, returns Promise
 
@@ -108,3 +113,26 @@ functions.RegisterAsyncFunction[FetchArgs, *FetchResult]("fetch", Fetch)
 - Use `os` package instead of deprecated `io/ioutil`
 - Error logging uses `_, _ = fmt.Fprintf(stderr, ...)` pattern
 - Package structure follows standard Go project layout with internal packages
+
+### Comment Style
+
+Code blocks (even within functions) should be separated with title-cased comments describing what the block does:
+
+```go
+// Create Runtime
+r := &Runtime{opts: qjs.Option{Context: ctx}}
+
+// Create QuickJS Context
+rt, err := qjs.New(r.opts)
+
+// Populate Globals
+if err := r.populateGlobals(); err != nil {
+    return nil, err
+}
+```
+
+For more complex blocks, use a hyphen to add elaboration:
+
+```go
+// Does Thing - We do this here because we need to do xyz...
+```
diff --git a/cmd/poiesis/main.go b/cmd/poiesis/main.go
index 4ee3ccc..a4adca0 100644
--- a/cmd/poiesis/main.go
+++ b/cmd/poiesis/main.go
@@ -5,11 +5,11 @@ import (
 	"fmt"
 	"os"
 
-	"reichard.io/poiesis/internal/functions"
 	"reichard.io/poiesis/internal/runtime"
 )
 
 func main() {
+	// Validate Arguments
 	if len(os.Args) < 2 {
 		fmt.Fprintln(os.Stderr, "Usage: poiesis <typescript-file>")
 		fmt.Fprintln(os.Stderr, "       poiesis -print-types")
@@ -18,7 +18,11 @@ func main() {
 
 	// Print Types
 	if os.Args[1] == "-print-types" {
-		fmt.Println(functions.GetFunctionDeclarations())
+		rt, err := runtime.New(context.Background())
+		if err != nil {
+			panic(err)
+		}
+		fmt.Println(rt.GetTypeDeclarations())
 		return
 	}
 
diff --git a/internal/functions/collector.go b/internal/functions/collector.go
deleted file mode 100644
index 5352698..0000000
--- a/internal/functions/collector.go
+++ /dev/null
@@ -1,170 +0,0 @@
-package functions
-
-import (
-	"fmt"
-	"reflect"
-	"strings"
-	"sync"
-)
-
-type typeCollector struct {
-	mu         sync.Mutex
-	types      map[string]string
-	paramTypes map[string]bool
-}
-
-func newTypeCollector() *typeCollector {
-	return &typeCollector{
-		types:      make(map[string]string),
-		paramTypes: make(map[string]bool),
-	}
-}
-
-func (tc *typeCollector) collectTypes(argsType reflect.Type, fnType reflect.Type) []string {
-	tc.mu.Lock()
-	defer tc.mu.Unlock()
-	tc.types = make(map[string]string)
-	tc.paramTypes = make(map[string]bool)
-
-	var result []string
-
-	tc.collectStruct(argsType, argsType.Name())
-
-	for i := 0; i < argsType.NumField(); i++ {
-		field := argsType.Field(i)
-		if field.Type.Kind() == reflect.Pointer || strings.Contains(field.Tag.Get("json"), ",omitempty") {
-			tc.collectParamType(field.Type)
-		}
-	}
-
-	if fnType.Kind() == reflect.Func && fnType.NumOut() > 0 {
-		lastIndex := fnType.NumOut() - 1
-		lastType := fnType.Out(lastIndex)
-
-		if lastType.Implements(reflect.TypeOf((*error)(nil)).Elem()) {
-			if fnType.NumOut() > 1 {
-				tc.collectType(fnType.Out(0))
-			}
-		} else {
-			tc.collectType(lastType)
-		}
-	}
-
-	for _, t := range tc.types {
-		result = append(result, t)
-	}
-
-	return result
-}
-
-func (tc *typeCollector) collectParamType(t reflect.Type) {
-	if t.Kind() == reflect.Pointer {
-		tc.collectParamType(t.Elem())
-		return
-	}
-
-	if t.Kind() == reflect.Struct && t.Name() != "" {
-		tc.paramTypes[t.Name()+" | null"] = true
-	}
-}
-
-func (tc *typeCollector) getParamTypes() map[string]bool {
-	return tc.paramTypes
-}
-
-func (tc *typeCollector) collectType(t reflect.Type) {
-	if t.Kind() == reflect.Pointer {
-		tc.collectType(t.Elem())
-		return
-	}
-
-	if t.Kind() == reflect.Struct {
-		name := t.Name()
-		if _, exists := tc.types[name]; !exists {
-			tc.collectStruct(t, name)
-		}
-	}
-}
-
-func (tc *typeCollector) collectStruct(t reflect.Type, name string) {
-	if t.Kind() != reflect.Struct {
-		return
-	}
-
-	var fields []string
-	for i := 0; i < t.NumField(); i++ {
-		field := t.Field(i)
-
-		if field.Anonymous || !field.IsExported() {
-			continue
-		}
-
-		fieldName := getFieldName(field)
-
-		var tsType string
-		var isOptional bool
-		isPointer := field.Type.Kind() == reflect.Pointer
-
-		if isPointer {
-			isOptional = true
-			tsType = goTypeToTSType(field.Type, false)
-		} else {
-			isOptional = strings.Contains(field.Tag.Get("json"), ",omitempty")
-			tsType = goTypeToTSType(field.Type, false)
-		}
-
-		if isOptional {
-			fieldName += "?"
-		}
-
-		fields = append(fields, fmt.Sprintf("%s: %s", fieldName, tsType))
-
-		tc.collectType(field.Type)
-	}
-
-	tc.types[name] = fmt.Sprintf("interface %s {%s}", name, strings.Join(fields, "; "))
-}
-
-func goTypeToTSType(t reflect.Type, isPointer bool) string {
-	if t.Kind() == reflect.Pointer {
-		return goTypeToTSType(t.Elem(), true)
-	}
-
-	baseType := ""
-	switch t.Kind() {
-	case reflect.String:
-		baseType = "string"
-	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		baseType = "number"
-	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
-		baseType = "number"
-	case reflect.Float32, reflect.Float64:
-		baseType = "number"
-	case reflect.Bool:
-		baseType = "boolean"
-	case reflect.Interface:
-		baseType = "any"
-	case reflect.Slice:
-		baseType = fmt.Sprintf("%s[]", goTypeToTSType(t.Elem(), false))
-	case reflect.Map:
-		if t.Key().Kind() == reflect.String && t.Elem().Kind() == reflect.Interface {
-			baseType = "Record<string, any>"
-		} else {
-			baseType = "Record<string, any>"
-		}
-	case reflect.Struct:
-		name := t.Name()
-		if name == "" {
-			baseType = "{}"
-		} else {
-			baseType = name
-		}
-	default:
-		baseType = "any"
-	}
-
-	if isPointer {
-		baseType += " | null"
-	}
-	return baseType
-}
diff --git a/internal/functions/registry.go b/internal/functions/registry.go
index 02f005a..21c77e4 100644
--- a/internal/functions/registry.go
+++ b/internal/functions/registry.go
@@ -5,44 +5,47 @@ import (
 	"reflect"
 	"strings"
 	"sync"
+
+	"reichard.io/poiesis/internal/tsconvert"
 )
 
 var (
 	functionRegistry = make(map[string]Function)
 	registryMutex    sync.RWMutex
-	collector        *typeCollector
 )
 
 func registerFunction[A Args, R any](name string, isAsync bool, fn GoFunc[A, R]) {
+	// Lock Registry
 	registryMutex.Lock()
 	defer registryMutex.Unlock()
 
-	if collector == nil {
-		collector = newTypeCollector()
-	}
-
+	// Validate Args Type
 	tType := reflect.TypeFor[A]()
 	if tType.Kind() != reflect.Struct {
 		panic(fmt.Sprintf("function %s: argument must be a struct type, got %v", name, tType))
 	}
 
+	// Collect Types and Generate Definition
 	fnType := reflect.TypeOf(fn)
-	types := collector.collectTypes(tType, fnType)
-	paramTypes := collector.getParamTypes()
+	types := tsconvert.CollectTypes(tType, fnType)
+	definition := tsconvert.GenerateFunctionDecl(name, tType, fnType, isAsync)
 
+	// Register Function
 	functionRegistry[name] = &functionImpl[A, R]{
 		name:       name,
 		fn:         fn,
-		types:      types,
-		definition: generateTypeScriptDefinition(name, tType, fnType, isAsync, paramTypes),
+		types:      types.All(),
+		definition: definition,
 		isAsync:    isAsync,
 	}
 }
 
 func GetFunctionDeclarations() string {
+	// Lock Registry
 	registryMutex.RLock()
 	defer registryMutex.RUnlock()
 
+	// Collect Type Definitions
 	typeDefinitions := make(map[string]bool)
 	var typeDefs []string
 	var functionDecls []string
@@ -57,6 +60,7 @@ func GetFunctionDeclarations() string {
 		functionDecls = append(functionDecls, fn.Definition())
 	}
 
+	// Build Result
 	result := strings.Join(typeDefs, "\n\n")
 	if len(result) > 0 && len(functionDecls) > 0 {
 		result += "\n\n"
@@ -66,10 +70,33 @@ func GetFunctionDeclarations() string {
 	return result
 }
 
-func GetRegisteredFunctions() map[string]Function {
+// GetTypeDeclarations returns all type declarations from all registered functions.
+// This is used for aggregating types across multiple functions.
+func GetTypeDeclarations() map[string]string {
+	// Lock Registry
 	registryMutex.RLock()
 	defer registryMutex.RUnlock()
 
+	// Collect All Types
+	allTypes := make(map[string]string)
+	for _, fn := range functionRegistry {
+		for name, def := range fn.Types() {
+			if existing, ok := allTypes[name]; ok && existing != def {
+				// Type Conflict Detected - Skip
+				continue
+			}
+			allTypes[name] = def
+		}
+	}
+	return allTypes
+}
+
+func GetRegisteredFunctions() map[string]Function {
+	// Lock Registry
+	registryMutex.RLock()
+	defer registryMutex.RUnlock()
+
+	// Copy Registry
 	result := make(map[string]Function, len(functionRegistry))
 	for k, v := range functionRegistry {
 		result[k] = v
@@ -78,9 +105,11 @@ func GetRegisteredFunctions() map[string]Function {
 }
 
 func RegisterFunction[T Args, R any](name string, fn GoFunc[T, R]) {
+	// Register Sync Function
 	registerFunction(name, false, fn)
 }
 
 func RegisterAsyncFunction[T Args, R any](name string, fn GoFunc[T, R]) {
+	// Register Async Function
 	registerFunction(name, true, fn)
 }
diff --git a/internal/functions/types.go b/internal/functions/types.go
index 0f54d9f..040c295 100644
--- a/internal/functions/types.go
+++ b/internal/functions/types.go
@@ -8,7 +8,7 @@ import (
 
 type Function interface {
 	Name() string
-	Types() []string
+	Types() map[string]string
 	Definition() string
 	IsAsync() bool
 	Arguments() []reflect.Type
@@ -25,7 +25,7 @@ type functionImpl[A Args, R any] struct {
 	name       string
 	fn         GoFunc[A, R]
 	definition string
-	types      []string
+	types      map[string]string
 	isAsync    bool
 }
 
@@ -33,7 +33,7 @@ func (b *functionImpl[A, R]) Name() string {
 	return b.name
 }
 
-func (b *functionImpl[A, R]) Types() []string {
+func (b *functionImpl[A, R]) Types() map[string]string {
 	return b.types
 }
 
@@ -50,6 +50,7 @@ func (b *functionImpl[A, R]) Function() any {
 }
 
 func (b *functionImpl[A, R]) Arguments() []reflect.Type {
+	// Collect Argument Types
 	var allTypes []reflect.Type
 
 	rType := reflect.TypeFor[A]()
@@ -73,17 +74,19 @@ func (b *functionImpl[A, R]) CallGeneric(ctx context.Context, allArgs []any) (ze
 	for i := range min(aVal.NumField(), len(allArgs)) {
 		field := aVal.Field(i)
 
+		// Validate Field is Settable
 		if !field.CanSet() {
 			return zeroR, errors.New("cannot set field")
 		}
 
+		// Validate and Set Field Value
 		argVal := reflect.ValueOf(allArgs[i])
 		if !argVal.Type().AssignableTo(field.Type()) {
 			return zeroR, errors.New("cannot assign field")
 		}
-
 		field.Set(argVal)
 	}
 
+	// Execute Function
 	return b.fn(ctx, fnArgs)
 }
diff --git a/internal/functions/typescript.go b/internal/functions/typescript.go
deleted file mode 100644
index 966677a..0000000
--- a/internal/functions/typescript.go
+++ /dev/null
@@ -1,73 +0,0 @@
-package functions
-
-import (
-	"fmt"
-	"reflect"
-	"strings"
-)
-
-func getFieldName(field reflect.StructField) string {
-	jsonTag := field.Tag.Get("json")
-	if jsonTag != "" && jsonTag != "-" {
-		name, _, _ := strings.Cut(jsonTag, ",")
-		return name
-	}
-	return field.Name
-}
-
-func generateTypeScriptDefinition(name string, argsType reflect.Type, fnType reflect.Type, isPromise bool, paramTypes map[string]bool) string {
-	if argsType.Kind() != reflect.Struct {
-		return ""
-	}
-
-	var params []string
-	for i := 0; i < argsType.NumField(); i++ {
-		field := argsType.Field(i)
-		fieldName := getFieldName(field)
-		goType := field.Type
-
-		var tsType string
-		var isOptional bool
-		isPointer := goType.Kind() == reflect.Pointer
-
-		if isPointer {
-			isOptional = true
-			tsType = goTypeToTSType(goType, true)
-			if !strings.Contains(tsType, " | null") {
-				tsType += " | null"
-			}
-		} else {
-			isOptional = strings.Contains(field.Tag.Get("json"), ",omitempty")
-			tsType = goTypeToTSType(goType, false)
-			if isOptional && paramTypes[tsType+" | null"] {
-				tsType += " | null"
-			}
-		}
-
-		if isOptional {
-			fieldName += "?"
-		}
-		params = append(params, fmt.Sprintf("%s: %s", fieldName, tsType))
-	}
-
-	returnSignature := "any"
-	if fnType.Kind() == reflect.Func && fnType.NumOut() > 0 {
-		lastIndex := fnType.NumOut() - 1
-		lastType := fnType.Out(lastIndex)
-
-		if lastType.Implements(reflect.TypeOf((*error)(nil)).Elem()) {
-			if fnType.NumOut() > 1 {
-				returnType := fnType.Out(0)
-				returnSignature = goTypeToTSType(returnType, returnType.Kind() == reflect.Pointer)
-			}
-		} else {
-			returnSignature = goTypeToTSType(lastType, lastType.Kind() == reflect.Pointer)
-		}
-	}
-
-	if isPromise {
-		returnSignature = fmt.Sprintf("Promise<%s>", returnSignature)
-	}
-
-	return fmt.Sprintf("declare function %s(%s): %s;", name, strings.Join(params, ", "), returnSignature)
-}
diff --git a/internal/functions/typescript_test.go b/internal/functions/typescript_test.go
index ae9eb2b..491e47c 100644
--- a/internal/functions/typescript_test.go
+++ b/internal/functions/typescript_test.go
@@ -2,7 +2,6 @@ package functions
 
 import (
 	"context"
-	"reflect"
 	"sync"
 	"testing"
 
@@ -17,19 +16,26 @@ type TestBasicArgs struct {
 func (t TestBasicArgs) Validate() error { return nil }
 
 func TestBasicType(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction("basic", func(ctx context.Context, args TestBasicArgs) (string, error) {
 		return args.Name, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function basic(name: string, age: number): string;")
 	assert.Contains(t, defs, "interface TestBasicArgs")
 }
 
 func resetRegistry() {
+	// Lock Registry
 	registryLock.Lock()
 	defer registryLock.Unlock()
+
+	// Clear Registry
 	functionRegistry = make(map[string]Function)
 }
 
@@ -46,11 +52,15 @@ type TestComplexArgs struct {
 func (t TestComplexArgs) Validate() error { return nil }
 
 func TestComplexTypes(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction("complex", func(ctx context.Context, args TestComplexArgs) (bool, error) {
 		return args.Flag, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function complex(items: number[], data: Record<string, any>, flag: boolean): boolean;")
 }
@@ -65,11 +75,15 @@ type TestNestedArgs struct {
 func (t TestNestedArgs) Validate() error { return nil }
 
 func TestNestedStruct(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction("nested", func(ctx context.Context, args TestNestedArgs) (string, error) {
 		return args.User.FirstName, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function nested(user: {}): string;")
 }
@@ -83,11 +97,15 @@ type TestOptionalArgs struct {
 func (t TestOptionalArgs) Validate() error { return nil }
 
 func TestOptionalFields(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction[TestOptionalArgs, string]("optional", func(ctx context.Context, args TestOptionalArgs) (string, error) {
 		return args.Name, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function optional(name: string, age?: number | null, score?: number | null): string;")
 }
@@ -104,11 +122,15 @@ type TestResultArgs struct {
 func (t TestResultArgs) Validate() error { return nil }
 
 func TestResultStruct(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction[TestResultArgs, TestResult]("result", func(ctx context.Context, args TestResultArgs) (TestResult, error) {
 		return TestResult{ID: 1}, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function result(input: string): TestResult;")
 	assert.Contains(t, defs, "interface TestResult {id: number; data: number[]}")
@@ -125,11 +147,15 @@ type TestAsyncResult struct {
 }
 
 func TestAsyncPromise(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Async Function
 	RegisterAsyncFunction[TestAsyncArgs, *TestAsyncStatus]("async", func(ctx context.Context, args TestAsyncArgs) (*TestAsyncStatus, error) {
 		return &TestAsyncStatus{Code: 200}, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function async(url: string): Promise<TestAsyncStatus | null>;")
 	assert.Contains(t, defs, "interface TestAsyncStatus")
@@ -150,11 +176,15 @@ type TestNestedPointerArgs struct {
 func (t TestNestedPointerArgs) Validate() error { return nil }
 
 func TestNestedPointerInResult(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction[TestNestedPointerArgs, *TestNestedPointerResult]("pointerResult", func(ctx context.Context, args TestNestedPointerArgs) (*TestNestedPointerResult, error) {
 		return &TestNestedPointerResult{Value: "test"}, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function pointerResult(id: number): TestNestedPointerResult | null;")
 }
@@ -166,11 +196,15 @@ type TestUintArgs struct {
 func (t TestUintArgs) Validate() error { return nil }
 
 func TestUintType(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction[TestUintArgs, uint]("uint", func(ctx context.Context, args TestUintArgs) (uint, error) {
 		return args.Value, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function uint(value: number): number;")
 }
@@ -182,11 +216,15 @@ type TestFloatArgs struct {
 func (t TestFloatArgs) Validate() error { return nil }
 
 func TestFloatType(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction[TestFloatArgs, float32]("float", func(ctx context.Context, args TestFloatArgs) (float32, error) {
 		return float32(args.Amount), nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function float(amount: number): number;")
 }
@@ -200,11 +238,15 @@ type TestPointerInArgs struct {
 func (t TestPointerInArgs) Validate() error { return nil }
 
 func TestNestedPointerStruct(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction[TestPointerInArgs, string]("nestedPointer", func(ctx context.Context, args TestPointerInArgs) (string, error) {
 		return "test", nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function nestedPointer(user?: {} | null): string;")
 }
@@ -216,58 +258,15 @@ type TestErrorOnlyArgs struct {
 func (t TestErrorOnlyArgs) Validate() error { return nil }
 
 func TestErrorOnlyReturn(t *testing.T) {
+	// Reset Registry
 	resetRegistry()
+
+	// Register Function
 	RegisterFunction[TestErrorOnlyArgs, struct{}]("errorOnly", func(ctx context.Context, args TestErrorOnlyArgs) (struct{}, error) {
 		return struct{}{}, nil
 	})
 
+	// Verify Declarations
 	defs := GetFunctionDeclarations()
 	assert.Contains(t, defs, "declare function errorOnly(input: string): {};")
 }
-
-func TestGoTypeToTSTypeBasic(t *testing.T) {
-	tests := []struct {
-		input    reflect.Type
-		inputPtr bool
-		expected string
-	}{
-		{reflect.TypeOf(""), false, "string"},
-		{reflect.TypeOf(0), false, "number"},
-		{reflect.TypeOf(int64(0)), false, "number"},
-		{reflect.TypeOf(uint(0)), false, "number"},
-		{reflect.TypeOf(3.14), false, "number"},
-		{reflect.TypeOf(float32(0.0)), false, "number"},
-		{reflect.TypeOf(true), false, "boolean"},
-		{reflect.TypeOf([]string{}), false, "string[]"},
-		{reflect.TypeOf([]int{}), false, "number[]"},
-		{reflect.TypeOf(map[string]any{}), false, "Record<string, any>"},
-		{reflect.TypeOf(map[string]int{}), false, "Record<string, any>"},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.expected, func(t *testing.T) {
-			result := goTypeToTSType(tt.input, tt.inputPtr)
-			assert.Equal(t, tt.expected, result)
-		})
-	}
-}
-
-type TestNestedStructField struct {
-	Inner struct {
-		Name string `json:"name"`
-	} `json:"inner"`
-}
-
-func TestGoTypeToTSTypeNestedStruct(t *testing.T) {
-	result := goTypeToTSType(reflect.TypeOf(TestNestedStructField{}), false)
-	assert.Equal(t, "TestNestedStructField", result)
-}
-
-type TestArrayField struct {
-	Items []string `json:"items"`
-}
-
-func TestGoTypeToTSTypeArray(t *testing.T) {
-	result := goTypeToTSType(reflect.TypeOf(TestArrayField{}), false)
-	assert.Equal(t, "TestArrayField", result)
-}
diff --git a/internal/runtime/options.go b/internal/runtime/options.go
index 23f7a32..9213669 100644
--- a/internal/runtime/options.go
+++ b/internal/runtime/options.go
@@ -6,12 +6,14 @@ type RuntimeOption func(*Runtime)
 
 func WithStdout(stdout io.Writer) RuntimeOption {
 	return func(r *Runtime) {
+		// Set Stdout
 		r.opts.Stdout = stdout
 	}
 }
 
 func WithStderr(stderr io.Writer) RuntimeOption {
 	return func(r *Runtime) {
+		// Set Stderr
 		r.opts.Stderr = stderr
 	}
 }
diff --git a/internal/runtime/runtime.go b/internal/runtime/runtime.go
index b11dbf3..e068fb6 100644
--- a/internal/runtime/runtime.go
+++ b/internal/runtime/runtime.go
@@ -14,8 +14,10 @@ import (
 )
 
 type Runtime struct {
-	ctx  *qjs.Context
-	opts qjs.Option
+	ctx       *qjs.Context
+	opts      qjs.Option
+	funcs     map[string]functions.Function
+	typeDecls map[string]string
 }
 
 func New(ctx context.Context, opts ...RuntimeOption) (*Runtime, error) {
@@ -41,8 +43,21 @@ func New(ctx context.Context, opts ...RuntimeOption) (*Runtime, error) {
 }
 
 func (r *Runtime) populateGlobals() error {
-	for name, fn := range functions.GetRegisteredFunctions() {
-		// Register Main Function
+	// Initialize Maps
+	r.funcs = make(map[string]functions.Function)
+	r.typeDecls = make(map[string]string)
+
+	// Load Requested Functions
+	allFuncs := functions.GetRegisteredFunctions()
+	for name, fn := range allFuncs {
+		r.funcs[name] = fn
+		if err := r.addFunctionTypes(fn); err != nil {
+			return fmt.Errorf("failed to add types for function %s: %w", name, err)
+		}
+	}
+
+	// Register Functions with QuickJS
+	for name, fn := range r.funcs {
 		if fn.IsAsync() {
 			r.ctx.SetAsyncFunc(name, func(this *qjs.This) {
 				qjsVal, err := callFunc(this, fn)
@@ -62,6 +77,37 @@ func (r *Runtime) populateGlobals() error {
 	return nil
 }
 
+// addFunctionTypes adds types from a function to the runtime's type declarations.
+// Returns an error if there's a type conflict (same name, different definition).
+func (r *Runtime) addFunctionTypes(fn functions.Function) error {
+	for name, def := range fn.Types() {
+		if existing, ok := r.typeDecls[name]; ok && existing != def {
+			return fmt.Errorf("type conflict: %s has conflicting definitions (existing: %s, new: %s)",
+				name, existing, def)
+		}
+		r.typeDecls[name] = def
+	}
+	return nil
+}
+
+// GetTypeDeclarations returns all TypeScript type declarations for this runtime.
+// Includes both type definitions and function declarations.
+func (r *Runtime) GetTypeDeclarations() string {
+	var decls []string
+
+	// Add Type Definitions
+	for _, def := range r.typeDecls {
+		decls = append(decls, def)
+	}
+
+	// Add Function Declarations
+	for _, fn := range r.funcs {
+		decls = append(decls, fn.Definition())
+	}
+
+	return strings.Join(decls, "\n\n")
+}
+
 func (r *Runtime) RunFile(filePath string) error {
 	tsFileContent, err := os.ReadFile(filePath)
 	if err != nil {
@@ -86,9 +132,9 @@ func (r *Runtime) RunCode(tsCode string) error {
 
 func (r *Runtime) transformCode(tsCode string) ([]byte, error) {
 	result := api.Transform(tsCode, api.TransformOptions{
-		Loader: api.LoaderTS,
-		Target: api.ES2022,
-		// Format:      api.FormatIIFE,
+		Loader:      api.LoaderTS,
+		Target:      api.ES2022,
+		Format:      api.FormatIIFE,
 		Sourcemap:   api.SourceMapNone,
 		TreeShaking: api.TreeShakingFalse,
 	})
diff --git a/internal/runtime/runtime_test.go b/internal/runtime/runtime_test.go
index f78b045..7e79576 100644
--- a/internal/runtime/runtime_test.go
+++ b/internal/runtime/runtime_test.go
@@ -23,11 +23,14 @@ func (t TestArgs) Validate() error {
 }
 
 func TestExecuteTypeScript(t *testing.T) {
+	// Create Buffers
 	var stdout, stderr bytes.Buffer
 
+	// Create Runtime
 	rt, err := New(context.Background(), WithStderr(&stderr), WithStdout(&stdout))
 	assert.NoError(t, err, "Expected no error")
 
+	// Create TypeScript Code
 	tsCode := `interface Person {
   name: string;
   age: number;
@@ -54,73 +57,107 @@ function calculateSum(a: number, b: number): number {
 console.log("Sum of 5 and 10 is: " + calculateSum(5, 10));
 `
 
+	// Create Temp File
 	tmpFile, err := os.CreateTemp("", "*.ts")
 	assert.NoError(t, err, "Failed to create temp file")
 	t.Cleanup(func() {
 		_ = os.Remove(tmpFile.Name())
 	})
 
+	// Write Code to File
 	_, err = tmpFile.WriteString(tsCode)
 	assert.NoError(t, err, "Failed to write to temp file")
 	err = tmpFile.Close()
 	assert.NoError(t, err, "Failed to close temp file")
 
+	// Run File
 	err = rt.RunFile(tmpFile.Name())
 
+	// Verify Execution
 	assert.NoError(t, err, "Expected no error")
 	assert.Empty(t, stderr.String(), "Expected no error output")
 
+	// Verify Output
 	output := stdout.String()
-
 	assert.Contains(t, output, "Hello, Alice!", "Should greet Alice")
 	assert.Contains(t, output, "You are 30 years old", "Should show age")
 	assert.Contains(t, output, "Email: alice@example.com", "Should show email")
 	assert.Contains(t, output, "Sum of 5 and 10 is: 15", "Should calculate sum correctly")
 
+	// Verify Line Count
 	lines := strings.Split(strings.TrimSpace(output), "\n")
 	assert.GreaterOrEqual(t, len(lines), 3, "Should have at least 3 output lines")
 }
 
 func TestAsyncFunctionResolution(t *testing.T) {
+	// Register Async Function
 	functions.RegisterAsyncFunction("resolveTest", func(_ context.Context, args TestArgs) (string, error) {
 		return "test-result", nil
 	})
 
+	// Create Runtime
 	r, err := New(context.Background())
 	require.NoError(t, err)
 
-	// Async functions need to be awaited in an async context
+	// Execute Async Function - Must be awaited in async context
 	result, err := r.ctx.Eval("test.js", qjs.Code(`async function run() { return await resolveTest("hello"); }; run()`))
 	require.NoError(t, err)
 	require.NotNil(t, result)
 	defer result.Free()
+
+	// Verify Result
 	assert.Equal(t, "test-result", result.String())
 }
 
 func TestAsyncFunctionRejection(t *testing.T) {
+	// Register Async Function that Returns Error
 	functions.RegisterAsyncFunction("rejectTest", func(_ context.Context, args TestArgs) (string, error) {
 		return "", assert.AnError
 	})
 
+	// Create Runtime
 	r, err := New(context.Background())
 	require.NoError(t, err)
 
-	// Rejected promises throw when awaited
+	// Execute Async Function - Rejected Promises Throw When Awaited
 	_, err = r.ctx.Eval("test.js", qjs.Code(`async function run() { return await rejectTest("hello"); }; run()`))
 	assert.Error(t, err)
 }
 
 func TestNonPromise(t *testing.T) {
+	// Register Sync Function
 	functions.RegisterFunction("nonPromiseTest", func(_ context.Context, args TestArgs) (string, error) {
 		return "sync-result", nil
 	})
 
+	// Create Runtime
 	r, err := New(context.Background())
 	assert.NoError(t, err)
 
+	// Execute Sync Function
 	result, err := r.ctx.Eval("test.js", qjs.Code(`nonPromiseTest("hello")`))
 	assert.NoError(t, err)
 	defer result.Free()
 
+	// Verify Result
 	assert.Equal(t, "sync-result", result.String())
 }
+
+func TestGetTypeDeclarations(t *testing.T) {
+	// Register Function
+	functions.RegisterFunction("testFunc", func(_ context.Context, args TestArgs) (string, error) {
+		return "result", nil
+	})
+
+	// Create Runtime
+	r, err := New(context.Background())
+	require.NoError(t, err)
+
+	// Get Type Declarations
+	decls := r.GetTypeDeclarations()
+
+	// Verify Declarations
+	assert.Contains(t, decls, "interface TestArgs")
+	assert.Contains(t, decls, "declare function testFunc")
+	assert.Contains(t, decls, "field1: string")
+}
diff --git a/internal/stdlib/fetch.go b/internal/stdlib/fetch.go
index 7903109..74b6a4a 100644
--- a/internal/stdlib/fetch.go
+++ b/internal/stdlib/fetch.go
@@ -42,9 +42,11 @@ type Response struct {
 }
 
 func Fetch(ctx context.Context, args FetchArgs) (Response, error) {
+	// Set Default Method and Headers
 	method := "GET"
 	headers := make(map[string]string)
 
+	// Apply Init Options
 	if args.Init != nil {
 		if args.Init.Method != "" {
 			method = args.Init.Method
@@ -54,15 +56,18 @@ func Fetch(ctx context.Context, args FetchArgs) (Response, error) {
 		}
 	}
 
+	// Create Request
 	req, err := http.NewRequestWithContext(ctx, method, args.Input, nil)
 	if err != nil {
 		return Response{}, fmt.Errorf("failed to create request: %w", err)
 	}
 
+	// Set Request Headers
 	for k, v := range headers {
 		req.Header.Set(k, v)
 	}
 
+	// Execute Request
 	resp, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return Response{}, fmt.Errorf("failed to fetch: %w", err)
@@ -71,11 +76,13 @@ func Fetch(ctx context.Context, args FetchArgs) (Response, error) {
 		_ = resp.Body.Close()
 	}()
 
+	// Read Response Body
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
 		return Response{}, fmt.Errorf("failed to read body: %w", err)
 	}
 
+	// Collect Response Headers
 	resultHeaders := make(map[string]string)
 	for key, values := range resp.Header {
 		if len(values) > 0 {
@@ -85,6 +92,7 @@ func Fetch(ctx context.Context, args FetchArgs) (Response, error) {
 		}
 	}
 
+	// Return Response
 	return Response{
 		OK:      resp.StatusCode >= 200 && resp.StatusCode < 300,
 		Status:  resp.StatusCode,
diff --git a/internal/stdlib/fetch_test.go b/internal/stdlib/fetch_test.go
index 7d009f4..4946670 100644
--- a/internal/stdlib/fetch_test.go
+++ b/internal/stdlib/fetch_test.go
@@ -11,7 +11,10 @@ import (
 )
 
 func TestFetch(t *testing.T) {
+	// Create Context
 	ctx := context.Background()
+
+	// Create Test Server
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		w.Header().Set("X-Custom-Header", "test-value")
@@ -20,9 +23,11 @@ func TestFetch(t *testing.T) {
 	}))
 	defer server.Close()
 
+	// Execute Fetch
 	result, err := Fetch(ctx, FetchArgs{Input: server.URL})
 	require.NoError(t, err)
 
+	// Verify Response
 	assert.True(t, result.OK)
 	assert.Equal(t, http.StatusOK, result.Status)
 	assert.Contains(t, result.Body, "Hello from httptest")
@@ -32,7 +37,10 @@ func TestFetch(t *testing.T) {
 }
 
 func TestFetchHTTPBin(t *testing.T) {
+	// Create Context
 	ctx := context.Background()
+
+	// Create Test Server
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		w.WriteHeader(http.StatusOK)
@@ -40,9 +48,11 @@ func TestFetchHTTPBin(t *testing.T) {
 	}))
 	defer server.Close()
 
+	// Execute Fetch
 	result, err := Fetch(ctx, FetchArgs{Input: server.URL})
 	require.NoError(t, err)
 
+	// Verify Response
 	assert.True(t, result.OK)
 	assert.Equal(t, http.StatusOK, result.Status)
 	assert.Contains(t, result.Body, `"args"`)
@@ -50,23 +60,33 @@ func TestFetchHTTPBin(t *testing.T) {
 }
 
 func TestFetchWith404(t *testing.T) {
+	// Create Context
 	ctx := context.Background()
+
+	// Execute Fetch
 	result, err := Fetch(ctx, FetchArgs{Input: "https://httpbin.org/status/404"})
 	require.NoError(t, err)
 
+	// Verify Response
 	assert.False(t, result.OK)
 	assert.Equal(t, http.StatusNotFound, result.Status)
 }
 
 func TestFetchWithInvalidURL(t *testing.T) {
+	// Create Context
 	ctx := context.Background()
+
+	// Execute Fetch - Should Fail
 	_, err := Fetch(ctx, FetchArgs{Input: "http://this-domain-does-not-exist-12345.com"})
 	assert.Error(t, err)
 	assert.Contains(t, err.Error(), "failed to fetch")
 }
 
 func TestFetchWithHeaders(t *testing.T) {
+	// Create Context
 	ctx := context.Background()
+
+	// Create Test Server
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		assert.Equal(t, "Bearer test-token", r.Header.Get("Authorization"))
 		assert.Equal(t, "GET", r.Method)
@@ -75,6 +95,7 @@ func TestFetchWithHeaders(t *testing.T) {
 	}))
 	defer server.Close()
 
+	// Configure Request Options
 	headers := map[string]string{
 		"Authorization": "Bearer test-token",
 	}
@@ -82,13 +103,18 @@ func TestFetchWithHeaders(t *testing.T) {
 		Method:  "GET",
 		Headers: headers,
 	}
+
+	// Execute Fetch with Headers
 	result, err := Fetch(ctx, FetchArgs{Input: server.URL, Init: options})
 	require.NoError(t, err)
 	assert.True(t, result.OK)
 }
 
 func TestFetchDefaults(t *testing.T) {
+	// Create Context
 	ctx := context.Background()
+
+	// Create Test Server
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		assert.Equal(t, "GET", r.Method, "default method should be GET")
 		w.WriteHeader(http.StatusOK)
@@ -96,6 +122,7 @@ func TestFetchDefaults(t *testing.T) {
 	}))
 	defer server.Close()
 
+	// Execute Fetch with Empty Options
 	options := &RequestInit{}
 	result, err := Fetch(ctx, FetchArgs{Input: server.URL, Init: options})
 	require.NoError(t, err)
diff --git a/internal/tsconvert/convert.go b/internal/tsconvert/convert.go
new file mode 100644
index 0000000..423fcd1
--- /dev/null
+++ b/internal/tsconvert/convert.go
@@ -0,0 +1,242 @@
+package tsconvert
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// ConvertType converts a Go reflect.Type to a TypeScript type string.
+func ConvertType(t reflect.Type) string {
+	return goTypeToTSType(t, false)
+}
+
+// goTypeToTSType converts a Go type to TypeScript type string.
+// isPointer tracks if we're inside a pointer chain.
+func goTypeToTSType(t reflect.Type, isPointer bool) string {
+	// Handle Pointer Types
+	if t.Kind() == reflect.Pointer {
+		return goTypeToTSType(t.Elem(), true)
+	}
+
+	// Determine Base Type
+	baseType := ""
+	switch t.Kind() {
+	case reflect.String:
+		baseType = "string"
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		baseType = "number"
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		baseType = "number"
+	case reflect.Float32, reflect.Float64:
+		baseType = "number"
+	case reflect.Bool:
+		baseType = "boolean"
+	case reflect.Interface:
+		baseType = "any"
+	case reflect.Slice:
+		baseType = fmt.Sprintf("%s[]", goTypeToTSType(t.Elem(), false))
+	case reflect.Map:
+		if t.Key().Kind() == reflect.String && t.Elem().Kind() == reflect.Interface {
+			baseType = "Record<string, any>"
+		} else {
+			baseType = "Record<string, any>"
+		}
+	case reflect.Struct:
+		name := t.Name()
+		if name == "" {
+			baseType = "{}"
+		} else {
+			baseType = name
+		}
+	default:
+		baseType = "any"
+	}
+
+	// Add Null for Pointer Types
+	if isPointer {
+		baseType += " | null"
+	}
+	return baseType
+}
+
+// CollectTypes extracts all type declarations from a function signature.
+// It analyzes the args type and return type to find all struct types.
+func CollectTypes(argsType, fnType reflect.Type) *TypeSet {
+	// Create TypeSet
+	ts := NewTypeSet()
+
+	// Collect Types from Args Struct
+	collectStructTypes(argsType, ts)
+
+	// Collect Types from Return Type
+	if fnType.Kind() == reflect.Func && fnType.NumOut() > 0 {
+		lastIndex := fnType.NumOut() - 1
+		lastType := fnType.Out(lastIndex)
+
+		if lastType.Implements(reflect.TypeOf((*error)(nil)).Elem()) {
+			if fnType.NumOut() > 1 {
+				collectType(fnType.Out(0), ts)
+			}
+		} else {
+			collectType(lastType, ts)
+		}
+	}
+
+	return ts
+}
+
+// collectType recursively collects struct types.
+func collectType(t reflect.Type, ts *TypeSet) {
+	// Handle Pointer Types
+	if t.Kind() == reflect.Pointer {
+		collectType(t.Elem(), ts)
+		return
+	}
+
+	// Collect Struct Types
+	if t.Kind() == reflect.Struct {
+		name := t.Name()
+		if name != "" {
+			// Only Process if Not Already Processed
+			if _, exists := ts.Get(name); !exists {
+				collectStructTypes(t, ts)
+			}
+		}
+	}
+}
+
+// collectStructTypes converts a Go struct to TypeScript interface and adds to TypeSet.
+func collectStructTypes(t reflect.Type, ts *TypeSet) {
+	// Validate Struct Type
+	if t.Kind() != reflect.Struct {
+		return
+	}
+
+	// Get Struct Name
+	name := t.Name()
+	if name == "" {
+		return // Skip Anonymous Structs
+	}
+
+	// Check if Already Processed
+	if _, exists := ts.Get(name); exists {
+		return
+	}
+
+	// Collect Fields
+	var fields []string
+	for i := 0; i < t.NumField(); i++ {
+		field := t.Field(i)
+
+		// Skip Anonymous and Unexported Fields
+		if field.Anonymous || !field.IsExported() {
+			continue
+		}
+
+		// Get Field Name
+		fieldName := getFieldName(field)
+
+		// Determine Type and Optionality
+		var tsType string
+		var isOptional bool
+		isPointer := field.Type.Kind() == reflect.Pointer
+
+		if isPointer {
+			isOptional = true
+			tsType = goTypeToTSType(field.Type, true)
+		} else {
+			isOptional = strings.Contains(field.Tag.Get("json"), ",omitempty")
+			tsType = goTypeToTSType(field.Type, false)
+		}
+
+		// Mark Optional Fields
+		if isOptional {
+			fieldName += "?"
+		}
+
+		fields = append(fields, fmt.Sprintf("%s: %s", fieldName, tsType))
+
+		// Recursively Collect Nested Types
+		collectType(field.Type, ts)
+	}
+
+	// Add Type Definition
+	definition := fmt.Sprintf("interface %s {%s}", name, strings.Join(fields, "; "))
+	_ = ts.Add(name, definition)
+}
+
+// getFieldName extracts the field name from json tag or uses the Go field name.
+func getFieldName(field reflect.StructField) string {
+	// Get JSON Tag
+	jsonTag := field.Tag.Get("json")
+	if jsonTag != "" && jsonTag != "-" {
+		name, _, _ := strings.Cut(jsonTag, ",")
+		return name
+	}
+
+	// Use Go Field Name
+	return field.Name
+}
+
+// GenerateFunctionDecl creates a TypeScript function declaration.
+func GenerateFunctionDecl(name string, argsType, fnType reflect.Type, isAsync bool) string {
+	// Validate Args Type
+	if argsType.Kind() != reflect.Struct {
+		return ""
+	}
+
+	// Collect Parameters
+	var params []string
+	for i := 0; i < argsType.NumField(); i++ {
+		field := argsType.Field(i)
+		fieldName := getFieldName(field)
+		goType := field.Type
+
+		// Determine Type and Optionality
+		var tsType string
+		var isOptional bool
+		isPointer := goType.Kind() == reflect.Pointer
+
+		if isPointer {
+			isOptional = true
+			tsType = goTypeToTSType(goType, true)
+			if !strings.Contains(tsType, " | null") {
+				tsType += " | null"
+			}
+		} else {
+			isOptional = strings.Contains(field.Tag.Get("json"), ",omitempty")
+			tsType = goTypeToTSType(goType, false)
+		}
+
+		// Mark Optional Fields
+		if isOptional {
+			fieldName += "?"
+		}
+		params = append(params, fmt.Sprintf("%s: %s", fieldName, tsType))
+	}
+
+	// Determine Return Type
+	returnSignature := "any"
+	if fnType.Kind() == reflect.Func && fnType.NumOut() > 0 {
+		lastIndex := fnType.NumOut() - 1
+		lastType := fnType.Out(lastIndex)
+
+		if lastType.Implements(reflect.TypeOf((*error)(nil)).Elem()) {
+			if fnType.NumOut() > 1 {
+				returnType := fnType.Out(0)
+				returnSignature = goTypeToTSType(returnType, returnType.Kind() == reflect.Pointer)
+			}
+		} else {
+			returnSignature = goTypeToTSType(lastType, lastType.Kind() == reflect.Pointer)
+		}
+	}
+
+	// Wrap in Promise for Async Functions
+	if isAsync {
+		returnSignature = fmt.Sprintf("Promise<%s>", returnSignature)
+	}
+
+	// Generate Declaration
+	return fmt.Sprintf("declare function %s(%s): %s;", name, strings.Join(params, ", "), returnSignature)
+}
diff --git a/internal/tsconvert/convert_test.go b/internal/tsconvert/convert_test.go
new file mode 100644
index 0000000..87b7e23
--- /dev/null
+++ b/internal/tsconvert/convert_test.go
@@ -0,0 +1,333 @@
+package tsconvert
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Test types for conversion
+type SimpleStruct struct {
+	Name  string `json:"name"`
+	Count int    `json:"count"`
+}
+
+type NestedStruct struct {
+	ID      int           `json:"id"`
+	Simple  SimpleStruct  `json:"simple"`
+	Pointer *SimpleStruct `json:"pointer,omitempty"`
+}
+
+type OptionalFields struct {
+	Required string  `json:"required"`
+	Optional *string `json:"optional,omitempty"`
+	Number   int     `json:"number,omitempty"`
+}
+
+type ComplexTypes struct {
+	Strings []string       `json:"strings"`
+	Numbers []int          `json:"numbers"`
+	Mapping map[string]any `json:"mapping"`
+	Nested  []SimpleStruct `json:"nested"`
+}
+
+func TestConvertType(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    any
+		expected string
+	}{
+		{"string", "", "string"},
+		{"int", int(0), "number"},
+		{"int8", int8(0), "number"},
+		{"int16", int16(0), "number"},
+		{"int32", int32(0), "number"},
+		{"int64", int64(0), "number"},
+		{"uint", uint(0), "number"},
+		{"float32", float32(0), "number"},
+		{"float64", float64(0), "number"},
+		{"bool", true, "boolean"},
+		{"interface", (*any)(nil), "any | null"},
+		{"slice of strings", []string{}, "string[]"},
+		{"slice of ints", []int{}, "number[]"},
+		{"map", map[string]any{}, "Record<string, any>"},
+		{"struct", SimpleStruct{}, "SimpleStruct"},
+		{"pointer to string", (*string)(nil), "string | null"},
+		{"pointer to struct", (*SimpleStruct)(nil), "SimpleStruct | null"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Get Input Type
+			var inputType reflect.Type
+			if tt.input == nil {
+				inputType = reflect.TypeOf((*any)(nil)).Elem()
+			} else {
+				inputType = reflect.TypeOf(tt.input)
+			}
+
+			// Convert Type
+			result := ConvertType(inputType)
+
+			// Verify Result
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+func TestCollectTypes(t *testing.T) {
+	t.Run("simple struct", func(t *testing.T) {
+		// Collect Types
+		argsType := reflect.TypeOf(SimpleStruct{})
+		fnType := reflect.TypeOf(func() (SimpleStruct, error) { return SimpleStruct{}, nil })
+		ts := CollectTypes(argsType, fnType)
+
+		// Verify TypeSet
+		require.NotNil(t, ts)
+		assert.Len(t, ts.All(), 1)
+
+		// Verify SimpleStruct Definition
+		def, ok := ts.Get("SimpleStruct")
+		assert.True(t, ok)
+		assert.Contains(t, def, "interface SimpleStruct")
+		assert.Contains(t, def, "name: string")
+		assert.Contains(t, def, "count: number")
+	})
+
+	t.Run("nested struct", func(t *testing.T) {
+		// Collect Types
+		argsType := reflect.TypeOf(NestedStruct{})
+		fnType := reflect.TypeOf(func() (NestedStruct, error) { return NestedStruct{}, nil })
+		ts := CollectTypes(argsType, fnType)
+
+		// Verify TypeSet
+		require.NotNil(t, ts)
+		all := ts.All()
+		assert.Len(t, all, 2) // NestedStruct and SimpleStruct
+
+		// Verify NestedStruct Definition
+		def, ok := ts.Get("NestedStruct")
+		assert.True(t, ok)
+		assert.Contains(t, def, "interface NestedStruct")
+		assert.Contains(t, def, "id: number")
+		assert.Contains(t, def, "simple: SimpleStruct")
+		assert.Contains(t, def, "pointer?: SimpleStruct | null")
+
+		// Verify SimpleStruct is Also Included
+		_, ok = ts.Get("SimpleStruct")
+		assert.True(t, ok)
+	})
+
+	t.Run("optional fields", func(t *testing.T) {
+		// Collect Types
+		argsType := reflect.TypeOf(OptionalFields{})
+		fnType := reflect.TypeOf(func() (OptionalFields, error) { return OptionalFields{}, nil })
+		ts := CollectTypes(argsType, fnType)
+
+		// Verify TypeSet
+		require.NotNil(t, ts)
+
+		// Verify OptionalFields Definition
+		def, ok := ts.Get("OptionalFields")
+		assert.True(t, ok)
+		assert.Contains(t, def, "required: string")
+		assert.Contains(t, def, "optional?: string | null")
+		assert.Contains(t, def, "number?: number")
+	})
+
+	t.Run("complex types", func(t *testing.T) {
+		// Collect Types
+		argsType := reflect.TypeOf(ComplexTypes{})
+		fnType := reflect.TypeOf(func() (ComplexTypes, error) { return ComplexTypes{}, nil })
+		ts := CollectTypes(argsType, fnType)
+
+		// Verify TypeSet
+		require.NotNil(t, ts)
+
+		// Verify ComplexTypes Definition
+		def, ok := ts.Get("ComplexTypes")
+		assert.True(t, ok)
+		assert.Contains(t, def, "strings: string[]")
+		assert.Contains(t, def, "numbers: number[]")
+		assert.Contains(t, def, "mapping: Record<string, any>")
+		assert.Contains(t, def, "nested: SimpleStruct[]")
+	})
+
+	t.Run("no return type", func(t *testing.T) {
+		// Collect Types
+		argsType := reflect.TypeOf(SimpleStruct{})
+		fnType := reflect.TypeOf(func() error { return nil })
+		ts := CollectTypes(argsType, fnType)
+
+		// Verify TypeSet - Only SimpleStruct from args
+		require.NotNil(t, ts)
+		assert.Len(t, ts.All(), 1)
+	})
+}
+
+func TestTypeSet(t *testing.T) {
+	t.Run("add and get", func(t *testing.T) {
+		// Create TypeSet
+		ts := NewTypeSet()
+
+		// Add Type
+		err := ts.Add("User", "interface User { name: string }")
+		require.NoError(t, err)
+
+		// Verify Type
+		def, ok := ts.Get("User")
+		assert.True(t, ok)
+		assert.Equal(t, "interface User { name: string }", def)
+	})
+
+	t.Run("duplicate same definition", func(t *testing.T) {
+		// Create TypeSet
+		ts := NewTypeSet()
+
+		// Add Type
+		err := ts.Add("User", "interface User { name: string }")
+		require.NoError(t, err)
+
+		// Add Same Type with Same Definition - Should Not Error
+		err = ts.Add("User", "interface User { name: string }")
+		require.NoError(t, err)
+
+		// Verify Count
+		assert.Len(t, ts.All(), 1)
+	})
+
+	t.Run("conflicting definitions", func(t *testing.T) {
+		// Create TypeSet
+		ts := NewTypeSet()
+
+		// Add Type
+		err := ts.Add("User", "interface User { name: string }")
+		require.NoError(t, err)
+
+		// Add Same Type with Different Definition - Should Error
+		err = ts.Add("User", "interface User { id: number }")
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "type conflict")
+		assert.Contains(t, err.Error(), "User")
+	})
+
+	t.Run("merge type sets", func(t *testing.T) {
+		// Create First TypeSet
+		ts1 := NewTypeSet()
+		err := ts1.Add("User", "interface User { name: string }")
+		require.NoError(t, err)
+
+		// Create Second TypeSet
+		ts2 := NewTypeSet()
+		err = ts2.Add("Post", "interface Post { title: string }")
+		require.NoError(t, err)
+
+		// Merge TypeSets
+		err = ts1.Merge(ts2)
+		require.NoError(t, err)
+
+		// Verify Merged Types
+		assert.Len(t, ts1.All(), 2)
+		_, ok := ts1.Get("User")
+		assert.True(t, ok)
+		_, ok = ts1.Get("Post")
+		assert.True(t, ok)
+	})
+
+	t.Run("merge with conflict", func(t *testing.T) {
+		// Create First TypeSet
+		ts1 := NewTypeSet()
+		err := ts1.Add("User", "interface User { name: string }")
+		require.NoError(t, err)
+
+		// Create Second TypeSet with Conflicting Type
+		ts2 := NewTypeSet()
+		err = ts2.Add("User", "interface User { id: number }")
+		require.NoError(t, err)
+
+		// Merge Should Fail Due to Conflict
+		err = ts1.Merge(ts2)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "type conflict")
+	})
+}
+
+func TestExtractName(t *testing.T) {
+	tests := []struct {
+		definition string
+		expected   string
+	}{
+		{"interface User { name: string }", "User"},
+		{"interface MyType { }", "MyType"},
+		{"type MyAlias = string", "MyAlias"},
+		{"type ComplexType = { a: number }", "ComplexType"},
+		{"invalid syntax here", ""},
+		{"", ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.definition, func(t *testing.T) {
+			// Extract Name
+			result := ExtractName(tt.definition)
+
+			// Verify Result
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+func TestGenerateFunctionDecl(t *testing.T) {
+	t.Run("simple function", func(t *testing.T) {
+		// Generate Declaration
+		argsType := reflect.TypeOf(SimpleStruct{})
+		fnType := reflect.TypeOf(func() (SimpleStruct, error) { return SimpleStruct{}, nil })
+		decl := GenerateFunctionDecl("myFunc", argsType, fnType, false)
+
+		// Verify Declaration
+		assert.Equal(t, "declare function myFunc(name: string, count: number): SimpleStruct;", decl)
+	})
+
+	t.Run("async function", func(t *testing.T) {
+		// Generate Declaration
+		argsType := reflect.TypeOf(SimpleStruct{})
+		fnType := reflect.TypeOf(func() (SimpleStruct, error) { return SimpleStruct{}, nil })
+		decl := GenerateFunctionDecl("myAsyncFunc", argsType, fnType, true)
+
+		// Verify Declaration
+		assert.Equal(t, "declare function myAsyncFunc(name: string, count: number): Promise<SimpleStruct>;", decl)
+	})
+
+	t.Run("function with optional fields", func(t *testing.T) {
+		// Generate Declaration
+		argsType := reflect.TypeOf(OptionalFields{})
+		fnType := reflect.TypeOf(func() (OptionalFields, error) { return OptionalFields{}, nil })
+		decl := GenerateFunctionDecl("optionalFunc", argsType, fnType, false)
+
+		// Verify Declaration
+		assert.Contains(t, decl, "required: string")
+		assert.Contains(t, decl, "optional?: string | null")
+		assert.Contains(t, decl, "number?: number")
+	})
+
+	t.Run("function with no return", func(t *testing.T) {
+		// Generate Declaration
+		argsType := reflect.TypeOf(SimpleStruct{})
+		fnType := reflect.TypeOf(func() error { return nil })
+		decl := GenerateFunctionDecl("noReturn", argsType, fnType, false)
+
+		// Verify Declaration
+		assert.Equal(t, "declare function noReturn(name: string, count: number): any;", decl)
+	})
+
+	t.Run("non-struct args returns empty", func(t *testing.T) {
+		// Generate Declaration
+		argsType := reflect.TypeOf("")
+		fnType := reflect.TypeOf(func() error { return nil })
+		decl := GenerateFunctionDecl("invalid", argsType, fnType, false)
+
+		// Verify Declaration
+		assert.Equal(t, "", decl)
+	})
+}
diff --git a/internal/tsconvert/types.go b/internal/tsconvert/types.go
new file mode 100644
index 0000000..71efb21
--- /dev/null
+++ b/internal/tsconvert/types.go
@@ -0,0 +1,92 @@
+// Package tsconvert provides utilities for converting Go types to TypeScript definitions.
+package tsconvert
+
+import (
+	"fmt"
+	"regexp"
+)
+
+// TypeDecl represents a TypeScript type declaration.
+type TypeDecl struct {
+	Name       string // e.g., "UserConfig"
+	Definition string // e.g., "interface UserConfig { name: string }"
+}
+
+// TypeSet manages a collection of type declarations with deduplication support.
+type TypeSet struct {
+	types map[string]string // name -> definition
+}
+
+// NewTypeSet creates a new empty TypeSet.
+func NewTypeSet() *TypeSet {
+	return &TypeSet{
+		types: make(map[string]string),
+	}
+}
+
+// Add adds a type declaration to the set.
+// Returns an error if a type with the same name but different definition already exists.
+func (ts *TypeSet) Add(name, definition string) error {
+	if existing, ok := ts.types[name]; ok {
+		if existing != definition {
+			return fmt.Errorf("type conflict: %s has conflicting definitions", name)
+		}
+		// Same name and definition, no conflict
+		return nil
+	}
+	ts.types[name] = definition
+	return nil
+}
+
+// Get retrieves a type definition by name.
+func (ts *TypeSet) Get(name string) (string, bool) {
+	def, ok := ts.types[name]
+	return def, ok
+}
+
+// All returns all type declarations as a map.
+func (ts *TypeSet) All() map[string]string {
+	result := make(map[string]string, len(ts.types))
+	for k, v := range ts.types {
+		result[k] = v
+	}
+	return result
+}
+
+// Names returns all type names in the set.
+func (ts *TypeSet) Names() []string {
+	names := make([]string, 0, len(ts.types))
+	for name := range ts.types {
+		names = append(names, name)
+	}
+	return names
+}
+
+// Merge merges another TypeSet into this one.
+// Returns an error if there are conflicting definitions.
+func (ts *TypeSet) Merge(other *TypeSet) error {
+	for name, def := range other.types {
+		if err := ts.Add(name, def); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// ExtractName extracts the type name from a TypeScript declaration.
+// Supports "interface Name {...}" and "type Name = ..." patterns.
+func ExtractName(definition string) string {
+	// Try interface pattern: "interface Name { ... }"
+	interfaceRe := regexp.MustCompile(`^interface\s+(\w+)`)
+	if matches := interfaceRe.FindStringSubmatch(definition); len(matches) > 1 {
+		return matches[1]
+	}
+
+	// Try type alias pattern: "type Name = ..."
+	typeRe := regexp.MustCompile(`^type\s+(\w+)`)
+	if matches := typeRe.FindStringSubmatch(definition); len(matches) > 1 {
+		return matches[1]
+	}
+
+	return ""
+}
diff --git a/plans/BUILTIN.md b/plans/BUILTIN.md
deleted file mode 100644
index 8da9931..0000000
--- a/plans/BUILTIN.md
+++ /dev/null
@@ -1,324 +0,0 @@
-# Builtin System Design
-
-## Overview
-
-Type-safe builtin system for exposing Go functions to TypeScript/JavaScript with automatic type conversion and defaults support.
-
-## Core Design
-
-### Single Argument Pattern
-
-All builtins accept a **single struct argument** on the Go side, but are called as **multi-argument functions** on the JavaScript side.
-
-```go
-type FetchArgs struct {
-    URL     string `json:"url"`
-    Options *FetchOptions `json:"options"`
-}
-
-func Fetch(args FetchArgs) (*FetchResult, error) {
-    // Implementation
-}
-
-// JavaScript calls:
-// fetch("https://example.com")
-// fetch("https://example.com", { method: "POST" })
-```
-
-**Mapping Rules:**
-- JavaScript arguments map **positionally** to struct fields in order
-- Field names in JavaScript come from `json:""` struct tag, or field name if tag is omitted
-- Missing JavaScript arguments only allowed for **pointer fields** (non-pointer fields must always be provided)
-
-### Default Values
-
-Argument structs **must** implement `Defaults()` receiver method to provide default values:
-
-```go
-type FetchOptions struct {
-    Method  string `json:"method"`
-    Headers map[string]string `json:"headers"`
-}
-
-func (f *FetchOptions) Defaults() *FetchOptions {
-    if f.Method == "" {
-        f.Method = "GET"
-    }
-    return f
-}
-
-// If called with just URL, Options will be nil initially,
-// then we create default: &FetchOptions{Method: "GET"}
-```
-
-**Defaults flow:**
-1. Create zero-value struct
-2. Fill in provided JavaScript arguments positionally
-3. Call `Defaults()` on the struct to fill in remaining defaults
-
-### Empty Arguments
-
-Zero-argument builtins must still use a struct (can be empty):
-
-```go
-// Helper type for no-argument builtins
-type EmptyArgs struct {}
-
-func Ping(args EmptyArgs) bool {
-    return true
-}
-
-// JavaScript: ping()
-```
-
-## Registration API
-
-```go
-package builtin
-
-// RegisterBuiltin registers a Go function as a builtin
-// The function must accept a single struct argument T and return (R, error) or R
-func RegisterBuiltin[T any, R any](name string, fn func(T) (R, error))
-```
-
-**Usage:**
-```go
-func init() {
-    builtin.RegisterBuiltin("fetch", Fetch)
-    builtin.RegisterBuiltin("add", Add)
-}
-```
-
-## Type Conversion
-
-### JavaScript → Go
-
-Automatic conversion from goja values to Go struct fields:
-
-| JavaScript | Go Type |
-|------------|---------|
-| string | string |
-| number | int, int8-64, uint, uint8-64, float32, float64 |
-| boolean | bool |
-| object/map | map[string]any |
-| null/undefined | nil (for pointer fields only) |
-
-**Struct Field Conversion:**
-- Primitives: converted by type
-- Maps: `map[string]any` → Go map with string keys
-- Nested structs: Recursive conversion to nested struct
-
-### Go → JavaScript (Return Types)
-
-Automatic conversion from Go return values to JavaScript:
-
-| Go Type | JavaScript |
-|---------|------------|
-| string, number, bool | primitive |
-| map[string]any | object |
-| map[string]string | object |
-| []any | array |
-| struct | object with fields from json tags |
-
-**Struct Return Types:**
-- Auto-converted to JavaScript objects
-- Field names from `json:""` struct tags
-- Nested structs become nested objects
-- No custom converters needed
-
-**Example:**
-```go
-type FetchResult struct {
-    OK      bool   `json:"ok"`
-    Status  int    `json:"status"`
-    Body    string `json:"body"`
-}
-
-// Returns: { ok: true, status: 200, body: "..." }
-```
-
-## Error Handling
-
-Go errors are automatically converted to JavaScript exceptions:
-
-```go
-func Fetch(args FetchArgs) (*FetchResult, error) {
-    if someError {
-        return nil, fmt.Errorf("fetch failed")
-    }
-    return result, nil
-}
-
-// JavaScript: fetch calls that error will throw
-```
-
-## TypeScript Declaration Generation
-
-TypeScript definitions are auto-generated from Go function signatures:
-
-```go
-// Go:
-func Fetch(args FetchArgs) (*FetchResult, error)
-
-// Generated TypeScript:
-declare function fetch(url: string, options?: FetchOptions): FetchResult | never;
-```
-
-**Type mapping:**
-- `string` → `string`
-- `int/int8-64/uint/uint8-64/float32/float64` → `number`
-- `bool` → `boolean`
-- `*T` → `T | null` (or `T` if optional)
-- `map[string]any` → `Record<string, any>`
-- `struct` → Interface with fields
-
-**Optional parameters:**
-- Pointer fields become optional parameters with `T | null`
-- Non-pointer fields are required
-
-## Implementation Notes
-
-### Reflection-Based Wrapping
-
-```go
-func createWrapper[T any, R any](fn func(T) (R, error)) func(*goja.Runtime, goja.FunctionCall) goja.Value {
-    return func(vm *goja.Runtime, call goja.FunctionCall) goja.Value {
-        // 1. Create zero-value struct
-        var args T
-        argsValue := reflect.ValueOf(&args).Elem()
-
-        // 2. Map JavaScript args to struct fields positionally
-        for i := 0; i < min(len(call.Arguments), argsValue.NumField()); i++ {
-            jsArg := call.Arguments[i]
-            field := argsValue.Field(i)
-
-            // Skip nil/undefined if field is pointer
-            if goja.IsUndefined(jsArg) || goja.IsNull(jsArg) {
-                if field.Kind() == reflect.Ptr {
-                    continue
-                }
-            }
-
-            // Convert and assign
-            converted, err := convertJSValueToGo(vm, jsArg, field.Type())
-            if err != nil {
-                panic(err)
-            }
-            field.Set(reflect.ValueOf(converted))
-        }
-
-        // 3. Call Defaults() if defined
-        if defaults, ok := args.(interface{ Defaults() T }); ok {
-            args = defaults.Defaults()
-        }
-
-        // 4. Call the Go function
-        result, err := fn(args)
-        if err != nil {
-            panic(err)
-        }
-
-        // 5. Convert return value to JavaScript
-        return convertGoValueToJS(vm, reflect.ValueOf(result))
-    }
-}
-```
-
-### Field Name Extraction
-
-```go
-func getFieldName(field reflect.StructField) string {
-    jsonTag := field.Tag.Get("json")
-    if jsonTag != "" && jsonTag != "-" {
-        name, _, _ := strings.Cut(jsonTag, ",")
-        return name
-    }
-    return field.Name
-}
-```
-
-## Migration Examples
-
-### Old → New
-
-**Old (current system):**
-```go
-func add(a, b int) int {
-    return a + b
-}
-
-// Register: builtin.RegisterBuiltin("add", add)
-// JS: add(5, 10)
-```
-
-**New system:**
-```go
-type AddArgs struct {
-    A int `json:"a"`
-    B int `json:"b"`
-}
-
-func add(args AddArgs) int {
-    return args.A + args.B
-}
-
-// Register: builtin.RegisterBuiltin("add", add)
-// JS: add(5, 10)          // positional
-// JS: add(a=5, b=10)      // named (if supported)
-```
-
-**Old fetch:**
-```go
-func Fetch(url string, options map[string]any) (*FetchResult, error)
-
-// Requires custom converter for result
-```
-
-**New fetch:**
-```go
-type FetchArgs struct {
-    URL     string `json:"url"`
-    Options *FetchOptions `json:"options"`
-}
-
-type FetchOptions struct {
-    Method  string `json:"method"`
-    Headers map[string]string `json:"headers"`
-}
-
-func (o *FetchOptions) Defaults() *FetchOptions {
-    if o.Method == "" {
-        o.Method = "GET"
-    }
-    return o
-}
-
-type FetchResult struct {
-    OK      bool   `json:"ok"`
-    Status  int    `json:"status"`
-    Body    string `json:"body"`
-}
-
-func Fetch(args FetchArgs) (*FetchResult, error) {
-    // Implementation - no custom converter needed
-}
-
-// JS: fetch("https://example.com")
-// JS: fetch("https://example.com", { method: "POST" })
-```
-
-## Testing
-
-All existing tests must pass after migration:
-
-- `internal/runtime/runtime_test.go`
-- `internal/runtime/standard/fetch_test.go`
-- `test_data/*.ts` test files
-
-Verify:
-- TypeScript definitions are correct
-- Positional argument mapping works
-- Defaults are applied correctly
-- Named JSON tags work
-- Error handling propagates
-- Return value conversion works