diff --git a/src/function/context.ts b/src/function/context.d.ts
similarity index 100%
rename from src/function/context.ts
rename to src/function/context.d.ts
diff --git a/src/function/event.ts b/src/function/event.d.ts
similarity index 100%
rename from src/function/event.ts
rename to src/function/event.d.ts
diff --git a/src/function/handler.ts b/src/function/handler.d.ts
similarity index 100%
rename from src/function/handler.ts
rename to src/function/handler.d.ts
diff --git a/src/function/index.ts b/src/function/index.d.ts
similarity index 100%
rename from src/function/index.ts
rename to src/function/index.d.ts
diff --git a/src/function/response.ts b/src/function/response.d.ts
similarity index 74%
rename from src/function/response.ts
rename to src/function/response.d.ts
index d6f2fb11..e05cd6b0 100644
--- a/src/function/response.ts
+++ b/src/function/response.d.ts
@@ -4,7 +4,7 @@ export interface Response {
     [header: string]: boolean | number | string
   }
   multiValueHeaders?: {
-    [header: string]: Array<boolean | number | string>
+    [header: string]: ReadonlyArray<boolean | number | string>
   }
   body: string
   isBase64Encoded?: boolean
diff --git a/src/lib/builder.ts b/src/lib/builder.d.ts
similarity index 100%
rename from src/lib/builder.ts
rename to src/lib/builder.d.ts