diff --git a/packages/event-handler/src/appsync-events/Router.ts b/packages/event-handler/src/appsync-events/Router.ts
index 38e189d65d..1298c82937 100644
--- a/packages/event-handler/src/appsync-events/Router.ts
+++ b/packages/event-handler/src/appsync-events/Router.ts
@@ -1,6 +1,9 @@
 import type { GenericLogger } from '@aws-lambda-powertools/commons/types';
 import { isRecord } from '@aws-lambda-powertools/commons/typeutils';
-import { getStringFromEnv, isDevMode } from '@aws-lambda-powertools/commons/utils/env';
+import {
+  getStringFromEnv,
+  isDevMode,
+} from '@aws-lambda-powertools/commons/utils/env';
 import type {
   OnPublishHandler,
   OnSubscribeHandler,
@@ -31,7 +34,7 @@ class Router {
    * Whether the router is running in development mode.
    */
   protected readonly isDev: boolean = false;
- 
+
   public constructor(options?: RouterOptions) {
     const alcLogLevel = getStringFromEnv({
       key: 'AWS_LAMBDA_LOG_LEVEL',
diff --git a/packages/event-handler/src/appsync-graphql/AppSyncGraphQLResolver.ts b/packages/event-handler/src/appsync-graphql/AppSyncGraphQLResolver.ts
index a338ef9c5b..6aede4c554 100644
--- a/packages/event-handler/src/appsync-graphql/AppSyncGraphQLResolver.ts
+++ b/packages/event-handler/src/appsync-graphql/AppSyncGraphQLResolver.ts
@@ -152,11 +152,7 @@ class AppSyncGraphQLResolver extends Router {
    * @param context - The AWS Lambda context object.
    * @param options - Optional parameters for the resolver, such as the scope of the handler.
    */
-  public async resolve(
-    event: unknown,
-    context: Context,
-    options?: ResolveOptions
-  ): Promise<unknown> {
+  public resolve(event: unknown, context: Context, options?: ResolveOptions) {
     if (Array.isArray(event)) {
       if (event.some((e) => !isAppSyncGraphQLEvent(e))) {
         this.logger.warn(
@@ -194,10 +190,10 @@ class AppSyncGraphQLResolver extends Router {
    * @param options - Optional resolve options for customizing resolver behavior.
    */
   async #withErrorHandling(
-    fn: () => Promise<unknown>,
+    fn: () => unknown,
     event: AppSyncResolverEvent<Record<string, unknown>>,
     options?: ResolveOptions
-  ): Promise<unknown> {
+  ) {
     try {
       return await fn();
     } catch (error) {
@@ -377,11 +373,11 @@ class AppSyncGraphQLResolver extends Router {
    * @param options - Optional parameters for the resolver, such as the scope of the handler.
    * @throws {ResolverNotFoundException} If no resolver is registered for the given field and type.
    */
-  async #executeSingleResolver(
+  #executeSingleResolver(
     event: AppSyncResolverEvent<Record<string, unknown>>,
     context: Context,
     options?: ResolveOptions
-  ): Promise<unknown> {
+  ): unknown {
     const { fieldName, parentTypeName: typeName } = event.info;
 
     const resolverHandlerOptions = this.resolverRegistry.resolve(
diff --git a/packages/event-handler/src/appsync-graphql/index.ts b/packages/event-handler/src/appsync-graphql/index.ts
index 9fe91122f4..bffc35bad1 100644
--- a/packages/event-handler/src/appsync-graphql/index.ts
+++ b/packages/event-handler/src/appsync-graphql/index.ts
@@ -1,7 +1,7 @@
 export { AppSyncGraphQLResolver } from './AppSyncGraphQLResolver.js';
 export {
-  ResolverNotFoundException,
   InvalidBatchResponseException,
+  ResolverNotFoundException,
 } from './errors.js';
 export {
   awsDate,
diff --git a/packages/event-handler/src/bedrock-agent/BedrockAgentFunctionResolver.ts b/packages/event-handler/src/bedrock-agent/BedrockAgentFunctionResolver.ts
index 5211ddade3..37e186dc69 100644
--- a/packages/event-handler/src/bedrock-agent/BedrockAgentFunctionResolver.ts
+++ b/packages/event-handler/src/bedrock-agent/BedrockAgentFunctionResolver.ts
@@ -146,7 +146,7 @@ class BedrockAgentFunctionResolver {
   public tool<TParams extends Record<string, ParameterValue>>(
     fn: ToolFunction<TParams>,
     config: Configuration
-  ): undefined {
+  ) {
     const { name } = config;
     if (this.#tools.has(name)) {
       this.#logger.warn(
diff --git a/packages/event-handler/src/rest/converters.ts b/packages/event-handler/src/rest/converters.ts
index d47302ebf6..6f8a1706f3 100644
--- a/packages/event-handler/src/rest/converters.ts
+++ b/packages/event-handler/src/rest/converters.ts
@@ -36,11 +36,11 @@ export const proxyEventToWebRequest = (
   const { domainName } = event.requestContext;
 
   const headers = new Headers();
-  for (const [name, value] of Object.entries(event.headers ?? {})) {
-    if (value != null) headers.set(name, value);
+  for (const [name, value] of Object.entries(event.headers)) {
+    if (value !== undefined) headers.set(name, value);
   }
 
-  for (const [name, values] of Object.entries(event.multiValueHeaders ?? {})) {
+  for (const [name, values] of Object.entries(event.multiValueHeaders)) {
     for (const value of values ?? []) {
       const headerValue = headers.get(name);
       if (!headerValue?.includes(value)) {
diff --git a/packages/event-handler/src/rest/middleware/cors.ts b/packages/event-handler/src/rest/middleware/cors.ts
index 25c780e39b..3a7d9b5f55 100644
--- a/packages/event-handler/src/rest/middleware/cors.ts
+++ b/packages/event-handler/src/rest/middleware/cors.ts
@@ -35,6 +35,7 @@ import {
  * }));
  * ```
  *
+ * @param options - Configuration options for CORS
  * @param options.origin - The origin to allow requests from
  * @param options.allowMethods - The HTTP methods to allow
  * @param options.allowHeaders - The headers to allow
diff --git a/packages/event-handler/src/rest/utils.ts b/packages/event-handler/src/rest/utils.ts
index e8fbd1e5d0..69636bd25b 100644
--- a/packages/event-handler/src/rest/utils.ts
+++ b/packages/event-handler/src/rest/utils.ts
@@ -150,7 +150,7 @@ export const isAPIGatewayProxyResult = (
  * ```
  */
 export const composeMiddleware = (middleware: Middleware[]): Middleware => {
-  return async ({ reqCtx, next }): Promise<HandlerResponse | void> => {
+  return async ({ reqCtx, next }) => {
     let index = -1;
     let result: HandlerResponse | undefined;
 
diff --git a/packages/event-handler/src/types/bedrock-agent.ts b/packages/event-handler/src/types/bedrock-agent.ts
index c649e1200d..8d99735cef 100644
--- a/packages/event-handler/src/types/bedrock-agent.ts
+++ b/packages/event-handler/src/types/bedrock-agent.ts
@@ -51,7 +51,10 @@ type ToolFunction<TParams = Record<string, ParameterValue>> = (
     event: BedrockAgentFunctionEvent;
     context: Context;
   }
-) => Promise<JSONValue | BedrockFunctionResponse>;
+) =>
+  | Promise<JSONValue | BedrockFunctionResponse>
+  | JSONValue
+  | BedrockFunctionResponse;
 
 /**
  * Tool in the Bedrock Agent Function Resolver.
@@ -159,7 +162,7 @@ type ResolverOptions = {
    *
    * When no logger is provided, we'll only log warnings and errors using the global `console` object.
    */
-  logger?: GenericLogger;
+  logger?: Pick<GenericLogger, 'debug' | 'warn' | 'error'>;
 };
 
 export type {
diff --git a/packages/event-handler/src/types/rest.ts b/packages/event-handler/src/types/rest.ts
index 1c9925ce22..9a7ddb5ddd 100644
--- a/packages/event-handler/src/types/rest.ts
+++ b/packages/event-handler/src/types/rest.ts
@@ -24,6 +24,7 @@ type ErrorHandler<T extends Error = Error> = (
 ) => Promise<HandlerResponse>;
 
 interface ErrorConstructor<T extends Error = Error> {
+  // biome-ignore lint/suspicious/noExplicitAny: this is a generic type that is intentionally open
   new (...args: any[]): T;
   prototype: T;
 }
@@ -57,7 +58,7 @@ type HandlerResponse = Response | JSONObject;
 
 type RouteHandler<TReturn = HandlerResponse> = (
   reqCtx: RequestContext
-) => Promise<TReturn>;
+) => Promise<TReturn> | TReturn;
 
 type HttpMethod = keyof typeof HttpVerbs;
 
@@ -78,12 +79,14 @@ type RestRouteOptions = {
   middleware?: Middleware[];
 };
 
+// biome-ignore lint/suspicious/noConfusingVoidType: To ensure next function is awaited
 type NextFunction = () => Promise<HandlerResponse | void>;
 
 type Middleware = (args: {
   reqCtx: RequestContext;
   next: NextFunction;
-}) => Promise<void | HandlerResponse>;
+  // biome-ignore lint/suspicious/noConfusingVoidType: To ensure next function is awaited
+}) => Promise<HandlerResponse | void>;
 
 type RouteRegistryOptions = {
   /**
@@ -176,4 +179,5 @@ export type {
   RouteRegistryOptions,
   ValidationResult,
   CompressionOptions,
+  NextFunction,
 };
diff --git a/packages/event-handler/tests/unit/appsync-events/AppSyncEventsResolver.test.ts b/packages/event-handler/tests/unit/appsync-events/AppSyncEventsResolver.test.ts
index 16da12ce63..512ff7a095 100644
--- a/packages/event-handler/tests/unit/appsync-events/AppSyncEventsResolver.test.ts
+++ b/packages/event-handler/tests/unit/appsync-events/AppSyncEventsResolver.test.ts
@@ -87,7 +87,7 @@ describe('Class: AppSyncEventsResolver', () => {
         public scope = 'scoped';
 
         @app.onPublish('/foo', { aggregate })
-        public async handleFoo(payloads: OnPublishAggregatePayload) {
+        public handleFoo(payloads: OnPublishAggregatePayload) {
           return payloads.map((payload) => {
             return {
               id: payload.id,
@@ -97,15 +97,15 @@ describe('Class: AppSyncEventsResolver', () => {
         }
 
         @app.onPublish('/bar')
-        public async handleBar(payload: string) {
+        public handleBar(payload: string) {
           return `${this.scope} ${payload}`;
         }
 
-        public async handler(event: unknown, context: Context) {
+        public handler(event: unknown, context: Context) {
           return this.stuff(event, context);
         }
 
-        async stuff(event: unknown, context: Context) {
+        stuff(event: unknown, context: Context) {
           return app.resolve(event, context, { scope: this });
         }
       }
@@ -146,15 +146,15 @@ describe('Class: AppSyncEventsResolver', () => {
       public scope = 'scoped';
 
       @app.onSubscribe('/foo')
-      public async handleFoo(payload: AppSyncEventsSubscribeEvent) {
+      public handleFoo(payload: AppSyncEventsSubscribeEvent) {
         console.debug(`${this.scope} ${payload.info.channel.path}`);
       }
 
-      public async handler(event: unknown, context: Context) {
+      public handler(event: unknown, context: Context) {
         return this.stuff(event, context);
       }
 
-      async stuff(event: unknown, context: Context) {
+      stuff(event: unknown, context: Context) {
         return app.resolve(event, context, { scope: this });
       }
     }
@@ -222,7 +222,7 @@ describe('Class: AppSyncEventsResolver', () => {
     async ({ error, message }) => {
       // Prepare
       const app = new AppSyncEventsResolver({ logger: console });
-      app.onSubscribe('/foo', async () => {
+      app.onSubscribe('/foo', () => {
         throw error;
       });
 
@@ -242,7 +242,7 @@ describe('Class: AppSyncEventsResolver', () => {
   it('throws an UnauthorizedException when thrown by the handler', async () => {
     // Prepare
     const app = new AppSyncEventsResolver({ logger: console });
-    app.onSubscribe('/foo', async () => {
+    app.onSubscribe('/foo', () => {
       throw new UnauthorizedException('nah');
     });
 
@@ -258,7 +258,7 @@ describe('Class: AppSyncEventsResolver', () => {
   it('returns the response of the onPublish handler', async () => {
     // Prepare
     const app = new AppSyncEventsResolver({ logger: console });
-    app.onPublish('/foo', async (payload) => {
+    app.onPublish('/foo', (payload) => {
       if (payload === 'foo') {
         return true;
       }
@@ -303,7 +303,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver({ logger: console });
     app.onPublish(
       '/foo',
-      async (payloads) => {
+      (payloads) => {
         return payloads.map((payload) => ({
           id: payload.id,
           payload: true,
@@ -353,7 +353,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver({ logger: console });
     app.onPublish(
       '/foo',
-      async () => {
+      () => {
         throw new Error('Error in handler');
       },
       { aggregate: true }
@@ -379,7 +379,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver({ logger: console });
     app.onPublish(
       '/foo',
-      async () => {
+      () => {
         throw new UnauthorizedException('nah');
       },
       { aggregate: true }
@@ -400,7 +400,7 @@ describe('Class: AppSyncEventsResolver', () => {
     const app = new AppSyncEventsResolver();
     app.onPublish(
       '/foo',
-      async () => {
+      () => {
         throw new Error('Error in handler');
       },
       { aggregate: true }
diff --git a/packages/event-handler/tests/unit/appsync-graphql/AppSyncGraphQLResolver.test.ts b/packages/event-handler/tests/unit/appsync-graphql/AppSyncGraphQLResolver.test.ts
index 06b653fcd9..1100a41005 100644
--- a/packages/event-handler/tests/unit/appsync-graphql/AppSyncGraphQLResolver.test.ts
+++ b/packages/event-handler/tests/unit/appsync-graphql/AppSyncGraphQLResolver.test.ts
@@ -93,7 +93,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver({ logger: console });
     app.resolver<{ id: string }>(
-      async ({ id }) => {
+      ({ id }) => {
         return {
           id,
           title: 'Post Title',
@@ -123,7 +123,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver({ logger: console });
     app.resolver<{ title: string; content: string }>(
-      async ({ title, content }) => {
+      ({ title, content }) => {
         return {
           id: '123',
           title,
@@ -166,7 +166,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     const app = new AppSyncGraphQLResolver();
     app.onMutation<{ title: string; content: string }>(
       'addPost',
-      async ({ title, content }) => {
+      ({ title, content }) => {
         return {
           id: '123',
           title,
@@ -196,16 +196,13 @@ describe('Class: AppSyncGraphQLResolver', () => {
   it('resolver function has access to event and context', async () => {
     // Prepare
     const app = new AppSyncGraphQLResolver({ logger: console });
-    app.onQuery<{ id: string }>(
-      'getPost',
-      async ({ id }, { event, context }) => {
-        return {
-          id,
-          event,
-          context,
-        };
-      }
-    );
+    app.onQuery<{ id: string }>('getPost', ({ id }, { event, context }) => {
+      return {
+        id,
+        event,
+        context,
+      };
+    });
 
     // Act
     const event = onGraphqlEventFactory('getPost', 'Query', { id: '123' });
@@ -227,7 +224,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       public scope = 'scoped';
 
       @app.onQuery('getPost')
-      public async handleGetPost({ id }: { id: string }) {
+      public handleGetPost({ id }: { id: string }) {
         return {
           id,
           scope: `${this.scope} id=${id}`,
@@ -235,7 +232,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       }
 
       @app.onMutation('addPost')
-      public async handleAddPost({
+      public handleAddPost({
         title,
         content,
       }: {
@@ -250,11 +247,11 @@ describe('Class: AppSyncGraphQLResolver', () => {
         };
       }
 
-      public async handler(event: unknown, context: Context) {
+      public handler(event: unknown, context: Context) {
         return this.stuff(event, context);
       }
 
-      async stuff(event: unknown, context: Context) {
+      stuff(event: unknown, context: Context) {
         return app.resolve(event, context, { scope: this });
       }
     }
@@ -295,9 +292,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       public scope = 'scoped';
 
       @app.batchResolver({ fieldName: 'batchGet' })
-      public async handleBatchGet(
-        events: AppSyncResolverEvent<{ id: number }>[]
-      ) {
+      public handleBatchGet(events: AppSyncResolverEvent<{ id: number }>[]) {
         const ids = events.map((event) => event.arguments.id);
         return ids.map((id) => ({
           id,
@@ -305,7 +300,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
         }));
       }
 
-      public async handler(event: unknown, context: Context) {
+      public handler(event: unknown, context: Context) {
         return app.resolve(event, context, { scope: this });
       }
     }
@@ -351,14 +346,14 @@ describe('Class: AppSyncGraphQLResolver', () => {
           throwOnError,
           aggregate: false,
         })
-        public async handleBatchGet({ id }: { id: string }) {
+        public handleBatchGet({ id }: { id: string }) {
           return {
             id,
             scope: `${this.scope} id=${id} throwOnError=${throwOnError} aggregate=false`,
           };
         }
 
-        public async handler(event: unknown, context: Context) {
+        public handler(event: unknown, context: Context) {
           return app.resolve(event, context, { scope: this });
         }
       }
@@ -395,7 +390,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
 
     class Lambda {
       @app.resolver({ fieldName: 'getPost' })
-      public async handleGetPost({ id }: { id: string }) {
+      public handleGetPost({ id }: { id: string }) {
         return {
           id,
           title: 'Post Title',
@@ -403,7 +398,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
         };
       }
 
-      public async handler(event: unknown, context: Context) {
+      public handler(event: unknown, context: Context) {
         return app.resolve(event, context, { scope: this });
       }
     }
@@ -445,7 +440,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       // Prepare
       const app = new AppSyncGraphQLResolver({ logger: console });
       app.resolver(
-        async () => {
+        () => {
           throw error;
         },
         {
@@ -677,9 +672,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
         @app.onBatchQuery('batchGet', {
           throwOnError,
         })
-        public async handleBatchGet(
-          events: AppSyncResolverEvent<{ id: number }>[]
-        ) {
+        public handleBatchGet(events: AppSyncResolverEvent<{ id: number }>[]) {
           const ids = events.map((event) => event.arguments.id);
           return ids.map((id) => ({
             id,
@@ -690,13 +683,11 @@ describe('Class: AppSyncGraphQLResolver', () => {
         @app.onBatchMutation('batchPut', {
           throwOnError,
         })
-        public async handleBatchPut(
-          _events: AppSyncResolverEvent<{ id: number }>[]
-        ) {
+        public handleBatchPut(_events: AppSyncResolverEvent<{ id: number }>[]) {
           return [this.scope, this.scope];
         }
 
-        public async handler(event: unknown, context: Context) {
+        public handler(event: unknown, context: Context) {
           return app.resolve(event, context, { scope: this });
         }
       }
@@ -776,9 +767,9 @@ describe('Class: AppSyncGraphQLResolver', () => {
         errorName: err.constructor.name,
       }));
 
-      app.onQuery('getUser', async () => {
+      app.onQuery('getUser', () => {
         throw errorClass === AggregateError
-          ? new errorClass([new Error()], message)
+          ? new errorClass([new Error('test error')], message)
           : new errorClass(message);
       });
 
@@ -800,7 +791,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver();
 
-    app.exceptionHandler(ValidationError, async (error) => {
+    app.exceptionHandler(ValidationError, (error) => {
       return {
         message: 'Validation failed',
         details: error.message,
@@ -808,7 +799,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.exceptionHandler(NotFoundError, async (error) => {
+    app.exceptionHandler(NotFoundError, (error) => {
       return {
         message: 'Resource not found',
         details: error.message,
@@ -816,7 +807,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.onQuery<{ id: string }>('getUser', async ({ id }) => {
+    app.onQuery<{ id: string }>('getUser', ({ id }) => {
       if (!id) {
         throw new ValidationError('User ID is required');
       }
@@ -853,7 +844,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver();
 
-    app.exceptionHandler(Error, async (error) => {
+    app.exceptionHandler(Error, (error) => {
       return {
         message: 'Generic error occurred',
         details: error.message,
@@ -861,7 +852,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.exceptionHandler(ValidationError, async (error) => {
+    app.exceptionHandler(ValidationError, (error) => {
       return {
         message: 'Validation failed',
         details: error.message,
@@ -869,7 +860,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.onQuery('getUser', async () => {
+    app.onQuery('getUser', () => {
       throw new ValidationError('Specific validation error');
     });
 
@@ -891,7 +882,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver();
 
-    app.exceptionHandler(AssertionError, async (error) => {
+    app.exceptionHandler(AssertionError, (error) => {
       return {
         message: 'Validation failed',
         details: error.message,
@@ -899,7 +890,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.onQuery('getUser', async () => {
+    app.onQuery('getUser', () => {
       throw new DatabaseError('Database connection failed');
     });
 
@@ -920,11 +911,11 @@ describe('Class: AppSyncGraphQLResolver', () => {
     const app = new AppSyncGraphQLResolver({ logger: console });
     const errorToBeThrown = new Error('Exception handler failed');
 
-    app.exceptionHandler(ValidationError, async () => {
+    app.exceptionHandler(ValidationError, () => {
       throw errorToBeThrown;
     });
 
-    app.onQuery('getUser', async () => {
+    app.onQuery('getUser', () => {
       throw new ValidationError('Original error');
     });
 
@@ -962,7 +953,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.onQuery('getUser', async () => {
+    app.onQuery('getUser', () => {
       throw new ValidationError('Sync error test');
     });
 
@@ -984,7 +975,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver();
 
-    app.exceptionHandler(RangeError, async (error) => {
+    app.exceptionHandler(RangeError, (error) => {
       return {
         message: 'This should not be called',
         details: error.message,
@@ -1009,7 +1000,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       public readonly scope = 'scoped';
 
       @app.exceptionHandler(ValidationError)
-      async handleValidationError(error: ValidationError) {
+      handleValidationError(error: ValidationError) {
         return {
           message: 'Decorator validation failed',
           details: error.message,
@@ -1029,7 +1020,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       }
 
       @app.onQuery('getUser')
-      async getUser({ id, name }: { id: string; name: string }) {
+      getUser({ id, name }: { id: string; name: string }) {
         if (!id) {
           throw new ValidationError('Decorator error test');
         }
@@ -1039,7 +1030,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
         return { id, name };
       }
 
-      async handler(event: unknown, context: Context) {
+      handler(event: unknown, context: Context) {
         return app.resolve(event, context, {
           scope: this,
         });
@@ -1078,7 +1069,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver({ logger: console });
 
-    app.exceptionHandler([ValidationError, NotFoundError], async (error) => {
+    app.exceptionHandler([ValidationError, NotFoundError], (error) => {
       return {
         message: 'User service error',
         details: error.message,
@@ -1087,7 +1078,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.onQuery<{ id: string }>('getId', async ({ id }) => {
+    app.onQuery<{ id: string }>('getId', ({ id }) => {
       if (!id) {
         throw new ValidationError('User ID is required for retrieval');
       }
@@ -1146,7 +1137,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       public readonly serviceName = 'OrderService';
 
       @app.exceptionHandler([ValidationError, NotFoundError])
-      async handleOrderErrors(error: ValidationError | NotFoundError) {
+      handleOrderErrors(error: ValidationError | NotFoundError) {
         return {
           message: `${this.serviceName} encountered an error`,
           details: error.message,
@@ -1157,7 +1148,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       }
 
       @app.onQuery('getOrder')
-      async getOrderById({ orderId }: { orderId: string }) {
+      getOrderById({ orderId }: { orderId: string }) {
         if (!orderId) {
           throw new ValidationError('Order ID is required');
         }
@@ -1170,7 +1161,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
         return { orderId, status: 'found', service: this.serviceName };
       }
 
-      async handler(event: unknown, context: Context) {
+      handler(event: unknown, context: Context) {
         const resolved = app.resolve(event, context, {
           scope: this,
         });
@@ -1228,7 +1219,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver();
 
-    app.exceptionHandler([ValidationError, TypeError], async (error) => {
+    app.exceptionHandler([ValidationError, TypeError], (error) => {
       return {
         message: 'Payment validation error',
         details: error.message,
@@ -1237,7 +1228,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
       };
     });
 
-    app.exceptionHandler(ValidationError, async (error) => {
+    app.exceptionHandler(ValidationError, (error) => {
       return {
         message: 'Specific payment validation error',
         details: error.message,
@@ -1248,7 +1239,7 @@ describe('Class: AppSyncGraphQLResolver', () => {
 
     app.onQuery<{ amount: number; currency: string }>(
       'getPayment',
-      async ({ amount, currency }) => {
+      ({ amount, currency }) => {
         if (!amount || amount <= 0) {
           throw new ValidationError('Invalid payment amount');
         }
@@ -1304,14 +1295,14 @@ describe('Class: AppSyncGraphQLResolver', () => {
     // Prepare
     const app = new AppSyncGraphQLResolver({ logger: console });
 
-    app.exceptionHandler([], async (error) => {
+    app.exceptionHandler([], (error) => {
       return {
         message: 'This should never be called',
         details: error.message,
       };
     });
 
-    app.onQuery<{ requestId: string }>('getId', async ({ requestId }) => {
+    app.onQuery<{ requestId: string }>('getId', ({ requestId }) => {
       if (requestId === 'validation-error') {
         throw new ValidationError('Invalid request format');
       }
diff --git a/packages/event-handler/tests/unit/bedrock-agent/BedrockAgentFunctionResolver.test.ts b/packages/event-handler/tests/unit/bedrock-agent/BedrockAgentFunctionResolver.test.ts
index 1b21f6694c..ae2e34b452 100644
--- a/packages/event-handler/tests/unit/bedrock-agent/BedrockAgentFunctionResolver.test.ts
+++ b/packages/event-handler/tests/unit/bedrock-agent/BedrockAgentFunctionResolver.test.ts
@@ -82,7 +82,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     const app = new BedrockAgentFunctionResolver();
 
     app.tool(
-      async (params: { arg: string }) => {
+      (params: { arg: string }) => {
         return params.arg;
       },
       {
@@ -101,7 +101,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     const app = new BedrockAgentFunctionResolver();
 
     app.tool(
-      async (params: { arg: string }) => {
+      (params: { arg: string }) => {
         return params.arg;
       },
       {
@@ -132,7 +132,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     ]);
 
     app.tool(
-      async (params: { a: number; b: number }) => {
+      (params: { a: number; b: number }) => {
         return params.a + params.b;
       },
       {
@@ -148,7 +148,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     );
 
     app.tool(
-      async (params: { a: number; b: number }) => {
+      (params: { a: number; b: number }) => {
         return params.a * params.b;
       },
       {
@@ -176,7 +176,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     const app = new BedrockAgentFunctionResolver({ logger });
 
     app.tool(
-      async (params: { arg: string }) => {
+      (params: { arg: string }) => {
         return params.arg;
       },
       {
@@ -186,7 +186,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     );
 
     app.tool(
-      async (params: { arg: string }) => {
+      (params: { arg: string }) => {
         return params.arg;
       },
       {
@@ -196,8 +196,8 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     );
 
     app.tool(
-      async (_params) => {
-        throw new Error();
+      () => {
+        throw new Error('test error');
       },
       {
         name: 'error',
@@ -220,7 +220,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     const app = new BedrockAgentFunctionResolver();
 
     app.tool(
-      async (_params, options) => {
+      (_params, options) => {
         return options?.event;
       },
       {
@@ -332,7 +332,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     const app = new BedrockAgentFunctionResolver();
 
     app.tool(
-      async () => {
+      () => {
         return new BedrockFunctionResponse({
           body: 'I am not sure',
           responseState: 'REPROMPT',
@@ -535,7 +535,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
       const app = new BedrockAgentFunctionResolver();
 
       app.tool(
-        async (_params, _options) => {
+        (_params, _options) => {
           throw toThrow;
         },
         {
@@ -564,7 +564,7 @@ describe('Class: BedrockAgentFunctionResolver', () => {
     const app = new BedrockAgentFunctionResolver();
 
     app.tool(
-      async (params, _options) => {
+      (params, _options) => {
         return `Hello, ${params.name}!`;
       },
       {
diff --git a/packages/event-handler/tests/unit/rest/RouteHandlerRegistry.test.ts b/packages/event-handler/tests/unit/rest/RouteHandlerRegistry.test.ts
index 42dccf5f24..f27671fd38 100644
--- a/packages/event-handler/tests/unit/rest/RouteHandlerRegistry.test.ts
+++ b/packages/event-handler/tests/unit/rest/RouteHandlerRegistry.test.ts
@@ -1,5 +1,8 @@
 import { describe, expect, it } from 'vitest';
-import { HttpVerbs } from '../../../src/rest/index.js';
+import {
+  HttpVerbs,
+  ParameterValidationError,
+} from '../../../src/rest/index.js';
 import { Route } from '../../../src/rest/Route.js';
 import { RouteHandlerRegistry } from '../../../src/rest/RouteHandlerRegistry.js';
 import type { Path } from '../../../src/types/rest.js';
@@ -570,20 +573,20 @@ describe('Class: RouteHandlerRegistry', () => {
     it('throws ParameterValidationError with multiple error messages for multiple invalid parameters', () => {
       // Prepare
       const registry = new RouteHandlerRegistry({ logger: console });
-      const handler = async () => ({ message: 'test' });
+      const handler = () => ({ message: 'test' });
       registry.register(
         new Route(HttpVerbs.GET, '/api/:version/:resource/:id', handler)
       );
 
       // Act & Assess
-      expect(async () => {
+      expect(() => {
         registry.resolve(HttpVerbs.GET, '/api/%20/users/%20');
-      }).rejects.toMatchObject({
-        issues: [
+      }).toThrow(
+        new ParameterValidationError([
           "Parameter 'version' cannot be empty",
           "Parameter 'id' cannot be empty",
-        ],
-      });
+        ])
+      );
     });
   });
 });
diff --git a/packages/event-handler/tests/unit/rest/Router/basic-routing.test.ts b/packages/event-handler/tests/unit/rest/Router/basic-routing.test.ts
index d4dffadb44..7ca29c9e2f 100644
--- a/packages/event-handler/tests/unit/rest/Router/basic-routing.test.ts
+++ b/packages/event-handler/tests/unit/rest/Router/basic-routing.test.ts
@@ -89,7 +89,7 @@ describe('Class: Router - Basic Routing', () => {
     const app = new Router();
     const testEvent = createTestEvent('/test', 'GET');
 
-    app.get('/test', async (reqCtx) => {
+    app.get('/test', (reqCtx) => {
       return {
         hasRequest: reqCtx.req instanceof Request,
         hasEvent: reqCtx.event === testEvent,
@@ -107,7 +107,7 @@ describe('Class: Router - Basic Routing', () => {
     expect(actual.hasContext).toBe(true);
   });
 
-  it('throws an internal server error for non-API Gateway events', async () => {
+  it('throws an internal server error for non-API Gateway events', () => {
     // Prepare
     const app = new Router();
     const nonApiGatewayEvent = { Records: [] }; // SQS-like event
@@ -123,10 +123,10 @@ describe('Class: Router - Basic Routing', () => {
     const app = new Router({
       prefix: '/todos',
     });
-    app.post('/', async () => {
+    app.post('/', () => {
       return { actualPath: '/todos' };
     });
-    app.get('/:todoId', async (reqCtx) => {
+    app.get('/:todoId', (reqCtx) => {
       return { actualPath: `/todos/${reqCtx.params.todoId}` };
     });
 
diff --git a/packages/event-handler/tests/unit/rest/Router/decorators.test.ts b/packages/event-handler/tests/unit/rest/Router/decorators.test.ts
index 0528e7a963..98c0ab7c5b 100644
--- a/packages/event-handler/tests/unit/rest/Router/decorators.test.ts
+++ b/packages/event-handler/tests/unit/rest/Router/decorators.test.ts
@@ -17,41 +17,41 @@ describe('Class: Router - Decorators', () => {
 
     class Lambda {
       @app.get('/test')
-      public async getTest() {
+      public getTest() {
         return { result: 'get-test' };
       }
 
       @app.post('/test')
-      public async postTest() {
+      public postTest() {
         return { result: 'post-test' };
       }
 
       @app.put('/test')
-      public async putTest() {
+      public putTest() {
         return { result: 'put-test' };
       }
 
       @app.patch('/test')
-      public async patchTest() {
+      public patchTest() {
         return { result: 'patch-test' };
       }
 
       @app.delete('/test')
-      public async deleteTest() {
+      public deleteTest() {
         return { result: 'delete-test' };
       }
 
       @app.head('/test')
-      public async headTest() {
+      public headTest() {
         return { result: 'head-test' };
       }
 
       @app.options('/test')
-      public async optionsTest() {
+      public optionsTest() {
         return { result: 'options-test' };
       }
 
-      public async handler(event: unknown, _context: Context) {
+      public handler(event: unknown, _context: Context) {
         return app.resolve(event, _context);
       }
     }
@@ -96,12 +96,12 @@ describe('Class: Router - Decorators', () => {
         public scope = 'class-scope';
 
         @app.get('/test', [middleware])
-        public async getTest() {
+        public getTest() {
           executionOrder.push('handler');
           return { result: `${this.scope}: decorator-with-middleware` };
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context, { scope: this });
         }
       }
@@ -149,41 +149,41 @@ describe('Class: Router - Decorators', () => {
 
         class Lambda {
           @app.get('/test', [middleware])
-          public async getTest() {
+          public getTest() {
             return { result: 'get-decorator-middleware' };
           }
 
           @app.post('/test', [middleware])
-          public async postTest() {
+          public postTest() {
             return { result: 'post-decorator-middleware' };
           }
 
           @app.put('/test', [middleware])
-          public async putTest() {
+          public putTest() {
             return { result: 'put-decorator-middleware' };
           }
 
           @app.patch('/test', [middleware])
-          public async patchTest() {
+          public patchTest() {
             return { result: 'patch-decorator-middleware' };
           }
 
           @app.delete('/test', [middleware])
-          public async deleteTest() {
+          public deleteTest() {
             return { result: 'delete-decorator-middleware' };
           }
 
           @app.head('/test', [middleware])
-          public async headTest() {
+          public headTest() {
             return { result: 'head-decorator-middleware' };
           }
 
           @app.options('/test', [middleware])
-          public async optionsTest() {
+          public optionsTest() {
             return { result: 'options-decorator-middleware' };
           }
 
-          public async handler(event: unknown, _context: Context) {
+          public handler(event: unknown, _context: Context) {
             return app.resolve(event, _context);
           }
         }
@@ -218,7 +218,7 @@ describe('Class: Router - Decorators', () => {
 
       class Lambda {
         @app.errorHandler(BadRequestError)
-        public async handleBadRequest(error: BadRequestError) {
+        public handleBadRequest(error: BadRequestError) {
           return {
             statusCode: HttpStatusCodes.BAD_REQUEST,
             error: 'Bad Request',
@@ -227,11 +227,11 @@ describe('Class: Router - Decorators', () => {
         }
 
         @app.get('/test')
-        public async getTest() {
+        public getTest() {
           throw new BadRequestError('test error');
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context);
         }
       }
@@ -265,7 +265,7 @@ describe('Class: Router - Decorators', () => {
         public scope = 'scoped';
 
         @app.notFound()
-        public async handleNotFound(error: NotFoundError) {
+        public handleNotFound(error: NotFoundError) {
           return {
             statusCode: HttpStatusCodes.NOT_FOUND,
             error: 'Not Found',
@@ -273,7 +273,7 @@ describe('Class: Router - Decorators', () => {
           };
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context, { scope: this });
         }
       }
@@ -306,7 +306,7 @@ describe('Class: Router - Decorators', () => {
 
       class Lambda {
         @app.methodNotAllowed()
-        public async handleMethodNotAllowed(error: MethodNotAllowedError) {
+        public handleMethodNotAllowed(error: MethodNotAllowedError) {
           return {
             statusCode: HttpStatusCodes.METHOD_NOT_ALLOWED,
             error: 'Method Not Allowed',
@@ -315,11 +315,11 @@ describe('Class: Router - Decorators', () => {
         }
 
         @app.get('/test')
-        public async getTest() {
+        public getTest() {
           throw new MethodNotAllowedError('POST not allowed');
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context);
         }
       }
@@ -353,7 +353,7 @@ describe('Class: Router - Decorators', () => {
         public scope = 'scoped';
 
         @app.errorHandler(BadRequestError)
-        public async handleBadRequest(error: BadRequestError) {
+        public handleBadRequest(error: BadRequestError) {
           return {
             statusCode: HttpStatusCodes.BAD_REQUEST,
             error: 'Bad Request',
@@ -362,11 +362,11 @@ describe('Class: Router - Decorators', () => {
         }
 
         @app.get('/test')
-        public async getTest() {
+        public getTest() {
           throw new BadRequestError('test error');
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context, { scope: this });
         }
       }
@@ -399,7 +399,7 @@ describe('Class: Router - Decorators', () => {
 
       class Lambda {
         @app.get('/test')
-        public async getTest(reqCtx: RequestContext) {
+        public getTest(reqCtx: RequestContext) {
           return {
             hasRequest: reqCtx.req instanceof Request,
             hasEvent: reqCtx.event === testEvent,
@@ -407,7 +407,7 @@ describe('Class: Router - Decorators', () => {
           };
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context);
         }
       }
@@ -431,7 +431,7 @@ describe('Class: Router - Decorators', () => {
 
       class Lambda {
         @app.errorHandler(BadRequestError)
-        public async handleBadRequest(
+        public handleBadRequest(
           error: BadRequestError,
           reqCtx: RequestContext
         ) {
@@ -446,11 +446,11 @@ describe('Class: Router - Decorators', () => {
         }
 
         @app.get('/test')
-        public async getTest() {
+        public getTest() {
           throw new BadRequestError('test error');
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context);
         }
       }
@@ -475,13 +475,13 @@ describe('Class: Router - Decorators', () => {
         public scope = 'scoped';
 
         @app.get('/test')
-        public async getTest() {
+        public getTest() {
           return {
             message: `${this.scope}: success`,
           };
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context, { scope: this });
         }
       }
diff --git a/packages/event-handler/tests/unit/rest/Router/error-handling.test.ts b/packages/event-handler/tests/unit/rest/Router/error-handling.test.ts
index f3921aa42b..87bc657628 100644
--- a/packages/event-handler/tests/unit/rest/Router/error-handling.test.ts
+++ b/packages/event-handler/tests/unit/rest/Router/error-handling.test.ts
@@ -107,7 +107,7 @@ describe('Class: Router - Error Handling', () => {
     vi.stubEnv('POWERTOOLS_DEV', '');
     const app = new Router();
 
-    app.errorHandler(BadRequestError, async () => {
+    app.errorHandler(BadRequestError, () => {
       throw new Error('Handler failed');
     });
 
@@ -486,7 +486,7 @@ describe('Class: Router - Error Handling', () => {
     // Prepare
     const app = new Router();
 
-    app.errorHandler(BadRequestError, async () => {
+    app.errorHandler(BadRequestError, () => {
       throw new NotFoundError('This error is thrown from the error handler');
     });
 
@@ -514,7 +514,7 @@ describe('Class: Router - Error Handling', () => {
     // Prepare
     const app = new Router();
 
-    app.errorHandler(BadRequestError, async () => {
+    app.errorHandler(BadRequestError, () => {
       throw new MethodNotAllowedError(
         'This error is thrown from the error handler'
       );
@@ -545,7 +545,7 @@ describe('Class: Router - Error Handling', () => {
     vi.stubEnv('POWERTOOLS_DEV', 'true');
     const app = new Router();
 
-    app.errorHandler(BadRequestError, async () => {
+    app.errorHandler(BadRequestError, () => {
       throw new Error('This error is thrown from the error handler');
     });
 
diff --git a/packages/event-handler/tests/unit/rest/Router/middleware.test.ts b/packages/event-handler/tests/unit/rest/Router/middleware.test.ts
index 4d66055914..93b6abc230 100644
--- a/packages/event-handler/tests/unit/rest/Router/middleware.test.ts
+++ b/packages/event-handler/tests/unit/rest/Router/middleware.test.ts
@@ -57,7 +57,7 @@ describe('Class: Router - Middleware', () => {
           }
       );
 
-      app.get(path as Path, middleware, async () => {
+      app.get(path as Path, middleware, () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -79,7 +79,7 @@ describe('Class: Router - Middleware', () => {
       app.use(createTrackingMiddleware('middleware1', executionOrder));
       app.use(createTrackingMiddleware('middleware2', executionOrder));
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -111,7 +111,7 @@ describe('Class: Router - Middleware', () => {
         )
       );
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -190,7 +190,7 @@ describe('Class: Router - Middleware', () => {
         await next();
       });
 
-      app.use(async ({ next }) => {
+      app.use(({ next }) => {
         next();
       });
 
@@ -221,7 +221,7 @@ describe('Class: Router - Middleware', () => {
       );
       app.use(createTrackingMiddleware('middleware2', executionOrder));
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -249,7 +249,7 @@ describe('Class: Router - Middleware', () => {
         throw new Error('Cleanup error');
       });
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -277,7 +277,7 @@ describe('Class: Router - Middleware', () => {
       app.use(createTrackingMiddleware('middleware1', executionOrder));
       app.use(createTrackingMiddleware('middleware2', executionOrder));
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         throw new Error('Handler error');
       });
@@ -305,7 +305,7 @@ describe('Class: Router - Middleware', () => {
       app.use(createNoNextMiddleware('middleware1', executionOrder));
       app.use(createTrackingMiddleware('middleware2', executionOrder));
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -334,7 +334,7 @@ describe('Class: Router - Middleware', () => {
         })
       );
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -369,7 +369,7 @@ describe('Class: Router - Middleware', () => {
         reqCtx.res.headers.set('x-request-id', '12345');
       });
 
-      app.get('/test', async () => ({ success: true }));
+      app.get('/test', () => ({ success: true }));
 
       // Act
       const result = await app.resolve(
@@ -457,7 +457,7 @@ describe('Class: Router - Middleware', () => {
         await next();
       });
 
-      app.get('/handler-precedence', async () => {
+      app.get('/handler-precedence', () => {
         const response = Response.json({ success: true });
         response.headers.set('x-before-handler', 'handler-value');
         return response;
@@ -542,12 +542,12 @@ describe('Class: Router - Middleware', () => {
         public scope = 'class-scope';
 
         @app.get('/test')
-        public async getTest() {
+        public getTest() {
           executionOrder.push('handler');
           return { message: `${this.scope}: success` };
         }
 
-        public async handler(event: unknown, _context: Context) {
+        public handler(event: unknown, _context: Context) {
           return app.resolve(event, _context, { scope: this });
         }
       }
@@ -586,7 +586,7 @@ describe('Class: Router - Middleware', () => {
         executionOrder
       );
 
-      app.get('/test', [routeMiddleware], async () => {
+      app.get('/test', [routeMiddleware], () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -619,7 +619,7 @@ describe('Class: Router - Middleware', () => {
         executionOrder
       );
 
-      app.get('/test', [routeMiddleware1, routeMiddleware2], async () => {
+      app.get('/test', [routeMiddleware1, routeMiddleware2], () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -646,7 +646,7 @@ describe('Class: Router - Middleware', () => {
 
       app.use(createTrackingMiddleware('global-middleware', executionOrder));
 
-      app.get('/test', async () => {
+      app.get('/test', () => {
         executionOrder.push('handler');
         return { success: true };
       });
@@ -674,7 +674,7 @@ describe('Class: Router - Middleware', () => {
         new Response('Route middleware response', { status: 403 })
       );
 
-      app.get('/test', [routeMiddleware], async () => {
+      app.get('/test', [routeMiddleware], () => {
         executionOrder.push('handler');
         return { success: true };
       });
diff --git a/packages/event-handler/tests/unit/rest/converters.test.ts b/packages/event-handler/tests/unit/rest/converters.test.ts
index e33c6136e6..e6f5a9a893 100644
--- a/packages/event-handler/tests/unit/rest/converters.test.ts
+++ b/packages/event-handler/tests/unit/rest/converters.test.ts
@@ -1,4 +1,3 @@
-import type { APIGatewayProxyEvent } from 'aws-lambda';
 import { describe, expect, it } from 'vitest';
 import {
   handlerResultToProxyResult,
@@ -6,36 +5,11 @@ import {
   proxyEventToWebRequest,
   webResponseToProxyResult,
 } from '../../../src/rest/index.js';
+import { createTestEvent } from './helpers.js';
 
 describe('Converters', () => {
   describe('proxyEventToWebRequest', () => {
-    const baseEvent: APIGatewayProxyEvent = {
-      httpMethod: 'GET',
-      path: '/test',
-      resource: '/test',
-      headers: {},
-      multiValueHeaders: {},
-      queryStringParameters: null,
-      multiValueQueryStringParameters: {},
-      pathParameters: null,
-      stageVariables: null,
-      requestContext: {
-        accountId: '123456789012',
-        apiId: 'test-api',
-        httpMethod: 'GET',
-        path: '/test',
-        requestId: 'test-request-id',
-        resourceId: 'test-resource',
-        resourcePath: '/test',
-        stage: 'test',
-        domainName: 'api.example.com',
-        identity: {
-          sourceIp: '127.0.0.1',
-        },
-      } as any,
-      isBase64Encoded: false,
-      body: null,
-    };
+    const baseEvent = createTestEvent('/test', 'GET');
 
     it('converts basic GET request', () => {
       // Prepare & Act
@@ -65,25 +39,24 @@ describe('Converters', () => {
 
     it('uses X-Forwarded-Proto header for protocol', () => {
       // Prepare
-      const event = {
-        ...baseEvent,
-        headers: { 'X-Forwarded-Proto': 'https' },
-      };
+      const event = createTestEvent('/test', 'GET', {
+        'X-Forwarded-Proto': 'http',
+      });
 
       // Act
       const request = proxyEventToWebRequest(event);
 
       // Assess
       expect(request).toBeInstanceOf(Request);
-      expect(request.url).toBe('https://api.example.com/test');
+      expect(request.url).toBe('http://api.example.com/test');
     });
 
-    it('handles null values in multiValueHeaders arrays', () => {
+    it('handles undefined values in multiValueHeaders arrays', () => {
       // Prepare
       const event = {
         ...baseEvent,
         multiValueHeaders: {
-          Accept: null as any,
+          Accept: undefined,
           'Custom-Header': ['value1'],
         },
       };
@@ -97,12 +70,12 @@ describe('Converters', () => {
       expect(request.headers.get('Custom-Header')).toBe('value1');
     });
 
-    it('handles null values in multiValueQueryStringParameters arrays', () => {
+    it('handles undefined values in multiValueQueryStringParameters arrays', () => {
       // Prepare
       const event = {
         ...baseEvent,
         multiValueQueryStringParameters: {
-          filter: null as any,
+          filter: undefined,
           sort: ['desc'],
         },
       };
@@ -117,7 +90,7 @@ describe('Converters', () => {
       expect(url.searchParams.get('sort')).toBe('desc');
     });
 
-    it('handles POST request with string body', async () => {
+    it('handles POST request with string body', () => {
       // Prepare
       const event = {
         ...baseEvent,
@@ -136,7 +109,7 @@ describe('Converters', () => {
       expect(request.headers.get('Content-Type')).toBe('application/json');
     });
 
-    it('decodes base64 encoded body', async () => {
+    it('decodes base64 encoded body', () => {
       // Prepare
       const originalText = 'Hello World';
       const base64Text = Buffer.from(originalText).toString('base64');
@@ -321,13 +294,13 @@ describe('Converters', () => {
       expect(url.searchParams.getAll('multi')).toEqual(['value1', 'value2']);
     });
 
-    it('skips null queryStringParameter values', () => {
+    it('skips undefined queryStringParameter values', () => {
       // Prepare
       const event = {
         ...baseEvent,
         queryStringParameters: {
           valid: 'value',
-          null: null as any,
+          null: undefined,
         },
       };
 
@@ -341,13 +314,13 @@ describe('Converters', () => {
       expect(url.searchParams.has('null')).toBe(false);
     });
 
-    it('skips null header values', () => {
+    it('skips undefined header values', () => {
       // Prepare
       const event = {
         ...baseEvent,
         headers: {
           'Valid-Header': 'value',
-          'Null-Header': null as any,
+          'Undefined-Header': undefined,
         },
       };
 
@@ -357,26 +330,7 @@ describe('Converters', () => {
       // Assess
       expect(request).toBeInstanceOf(Request);
       expect(request.headers.get('Valid-Header')).toBe('value');
-      expect(request.headers.get('Null-Header')).toBe(null);
-    });
-
-    it('handles null/undefined collections', () => {
-      // Prepare
-      const event = {
-        ...baseEvent,
-        headers: null as any,
-        multiValueHeaders: null as any,
-        queryStringParameters: null as any,
-        multiValueQueryStringParameters: null as any,
-      };
-
-      // Act
-      const request = proxyEventToWebRequest(event);
-
-      // Assess
-      expect(request).toBeInstanceOf(Request);
-      expect(request.method).toBe('GET');
-      expect(request.url).toBe('https://api.example.com/test');
+      expect(request.headers.get('Undefined-Header')).toBe(null);
     });
   });
 
@@ -568,7 +522,7 @@ describe('Converters', () => {
       expect(result.headers.get('content-type')).toBe('text/plain');
     });
 
-    it('converts APIGatewayProxyResult with multiValueHeaders', async () => {
+    it('converts APIGatewayProxyResult with multiValueHeaders', () => {
       // Prepare
       const proxyResult = {
         statusCode: 200,
@@ -590,7 +544,7 @@ describe('Converters', () => {
       );
     });
 
-    it('converts plain object to JSON Response with default headers', async () => {
+    it('converts plain object to JSON Response with default headers', () => {
       // Prepare
       const obj = { message: 'success' };
 
@@ -604,7 +558,7 @@ describe('Converters', () => {
       expect(result.headers.get('Content-Type')).toBe('application/json');
     });
 
-    it('uses provided headers for plain object', async () => {
+    it('uses provided headers for plain object', () => {
       // Prepare
       const obj = { message: 'success' };
       const headers = new Headers({ 'x-custom': 'value' });
@@ -617,7 +571,7 @@ describe('Converters', () => {
       expect(result.headers.get('x-custom')).toBe('value');
     });
 
-    it('handles APIGatewayProxyResult with undefined headers', async () => {
+    it('handles APIGatewayProxyResult with undefined headers', () => {
       // Prepare
       const proxyResult = {
         statusCode: 200,
@@ -634,7 +588,7 @@ describe('Converters', () => {
       expect(result.status).toBe(200);
     });
 
-    it('handles APIGatewayProxyResult with undefined multiValueHeaders', async () => {
+    it('handles APIGatewayProxyResult with undefined multiValueHeaders', () => {
       // Prepare
       const proxyResult = {
         statusCode: 200,
@@ -651,7 +605,7 @@ describe('Converters', () => {
       expect(result.headers.get('content-type')).toBe('text/plain');
     });
 
-    it('handles APIGatewayProxyResult with undefined values in multiValueHeaders', async () => {
+    it('handles APIGatewayProxyResult with undefined values in multiValueHeaders', () => {
       // Prepare
       const proxyResult = {
         statusCode: 200,
diff --git a/packages/event-handler/tests/unit/rest/helpers.ts b/packages/event-handler/tests/unit/rest/helpers.ts
index 4f04e0e3c1..aeb4e51c2d 100644
--- a/packages/event-handler/tests/unit/rest/helpers.ts
+++ b/packages/event-handler/tests/unit/rest/helpers.ts
@@ -19,7 +19,7 @@ export const createTestEvent = (
   requestContext: {
     httpMethod,
     path,
-    domainName: 'localhost',
+    domainName: 'api.example.com',
   } as APIGatewayProxyEvent['requestContext'],
   resource: '',
 });
@@ -40,7 +40,7 @@ export const createThrowingMiddleware = (
   executionOrder: string[],
   errorMessage: string
 ): Middleware => {
-  return async () => {
+  return () => {
     executionOrder.push(name);
     throw new Error(errorMessage);
   };
@@ -51,7 +51,7 @@ export const createReturningMiddleware = (
   executionOrder: string[],
   response: HandlerResponse
 ): Middleware => {
-  return async () => {
+  return () => {
     executionOrder.push(name);
     return response;
   };
@@ -61,7 +61,7 @@ export const createNoNextMiddleware = (
   name: string,
   executionOrder: string[]
 ): Middleware => {
-  return async () => {
+  return () => {
     executionOrder.push(name);
     // Intentionally doesn't call next()
   };
diff --git a/packages/event-handler/tests/unit/rest/middleware/compress.test.ts b/packages/event-handler/tests/unit/rest/middleware/compress.test.ts
index 0aa8a1e289..653bb62afd 100644
--- a/packages/event-handler/tests/unit/rest/middleware/compress.test.ts
+++ b/packages/event-handler/tests/unit/rest/middleware/compress.test.ts
@@ -22,7 +22,7 @@ describe('Compress Middleware', () => {
 
   it('compresses response when conditions are met', async () => {
     // Prepare
-    app.get('/test', async () => {
+    app.get('/test', () => {
       return body;
     });
 
@@ -49,7 +49,7 @@ describe('Compress Middleware', () => {
           'content-length': '1',
         }),
       ],
-      async () => {
+      () => {
         return { test: 'x' };
       }
     );
@@ -65,7 +65,7 @@ describe('Compress Middleware', () => {
   it('skips compression for HEAD requests', async () => {
     // Prepare
     const headEvent = createTestEvent('/test', 'HEAD');
-    app.head('/test', async () => {
+    app.head('/test', () => {
       return body;
     });
 
@@ -93,7 +93,7 @@ describe('Compress Middleware', () => {
           'content-length': '2000',
         }),
       ],
-      async () => {
+      () => {
         return body;
       }
     );
@@ -118,7 +118,7 @@ describe('Compress Middleware', () => {
           'cache-control': 'no-transform',
         }),
       ],
-      async () => {
+      () => {
         return body;
       }
     );
@@ -144,7 +144,7 @@ describe('Compress Middleware', () => {
           'content-length': '2000',
         }),
       ],
-      async () => {
+      () => {
         return body;
       }
     );
@@ -162,7 +162,7 @@ describe('Compress Middleware', () => {
     const noCompressionEvent = createTestEvent('/test', 'GET', {
       'Accept-Encoding': 'identity',
     });
-    app.get('/test', async () => {
+    app.get('/test', () => {
       return body;
     });
 
diff --git a/packages/event-handler/tests/unit/rest/utils.test.ts b/packages/event-handler/tests/unit/rest/utils.test.ts
index 5082eb6608..2c8db5db78 100644
--- a/packages/event-handler/tests/unit/rest/utils.test.ts
+++ b/packages/event-handler/tests/unit/rest/utils.test.ts
@@ -469,7 +469,7 @@ describe('Path Utilities', () => {
       const composed = composeMiddleware(middleware);
       await composed({
         reqCtx: mockOptions,
-        next: async () => {
+        next: () => {
           executionOrder.push('handler');
         },
       });
@@ -488,7 +488,7 @@ describe('Path Utilities', () => {
         async ({ next }) => {
           await next();
         },
-        async () => {
+        () => {
           return { shortCircuit: true };
         },
       ];
@@ -496,7 +496,7 @@ describe('Path Utilities', () => {
       const composed = composeMiddleware(middleware);
       const result = await composed({
         reqCtx: mockOptions,
-        next: async () => {
+        next: () => {
           return { handler: true };
         },
       });
@@ -514,7 +514,7 @@ describe('Path Utilities', () => {
       const composed = composeMiddleware(middleware);
       const result = await composed({
         reqCtx: mockOptions,
-        next: async () => {
+        next: () => {
           return { handler: true };
         },
       });
@@ -541,7 +541,7 @@ describe('Path Utilities', () => {
       const composed = composeMiddleware([]);
       const result = await composed({
         reqCtx: mockOptions,
-        next: async () => {
+        next: () => {
           return { handler: true };
         },
       });
@@ -559,7 +559,7 @@ describe('Path Utilities', () => {
       const composed = composeMiddleware(middleware);
       const result = await composed({
         reqCtx: mockOptions,
-        next: async () => {
+        next: () => {
           return undefined;
         },
       });