diff --git a/src/handler.test.ts b/src/handler.test.ts
index 3b0a479..998d460 100644
--- a/src/handler.test.ts
+++ b/src/handler.test.ts
@@ -3,14 +3,13 @@ import assert from 'node:assert';
 import { ValidationError } from './error';
 import { Request, Response } from 'express';
 import { describe, it, mock } from 'node:test';
-import { CacheType, OpenAIServiceType } from './util';
+import { CacheType, OpenAIServiceType } from './types';
 import {
 	getDownloadCommitDotShHandler,
 	getHealthzHandler,
 	getIndexHandler,
 	postGenerateCommitMessageHandler,
 } from './handler';
-import { createSourceMapSource } from 'typescript';
 
 describe('getHealthzHandler', () => {
 	it('should return ok', () => {
diff --git a/src/handler.ts b/src/handler.ts
index f752e07..fe78716 100644
--- a/src/handler.ts
+++ b/src/handler.ts
@@ -1,12 +1,6 @@
 import { ValidationError } from './error';
 import { Request, Response } from 'express';
-import { OpenAIServiceType, CacheType } from './util';
-
-interface GenerateCommitMessageRequest extends Request {
-	body: {
-		diff: string;
-	};
-}
+import { GenerateCommitMessageRequest, CacheType, OpenAIServiceType } from './types';
 
 export function getHealthzHandler() {
 	return (req: Request, res: Response) => {
@@ -49,7 +43,7 @@ export function getIndexHandler(extractDomain: (req: Request) => string, commitD
 }
 
 export function postGenerateCommitMessageHandler(OpenAIService: OpenAIServiceType) {
-	return async (req: Request, res: Response) => {
+	return async (req: GenerateCommitMessageRequest, res: Response) => {
 		const { diff } = req.body;
 
 		if (!diff || !diff.trim().length) {
@@ -60,6 +54,7 @@ export function postGenerateCommitMessageHandler(OpenAIService: OpenAIServiceTyp
 		// Tokens in GPT-3 are more complex and can be part of a word, punctuation, or whitespace.
 		// For more accurate token counting, consider using a tokenizer library.
 		const MAX_TOKENS = 16385;
+
 		const tokenLength = diff.split(/\s+/).length;
 
 		if (tokenLength > MAX_TOKENS) {
diff --git a/src/types.ts b/src/types.ts
new file mode 100644
index 0000000..6287a7c
--- /dev/null
+++ b/src/types.ts
@@ -0,0 +1,32 @@
+import { OpenAI } from 'openai';
+import { Request } from 'express';
+
+export interface GenerateCommitMessageRequest extends Request {
+	body: {
+		diff: string;
+	};
+}
+
+export interface CacheType {
+	set(key: string, value: string): void;
+	get(key: string): string | null;
+	clear(key: string): void;
+}
+
+export interface OpenAIServiceType {
+	openai: OpenAI;
+	generateCommitMessage(diff: string): Promise<string | null>;
+}
+
+export interface ConfigItem<T> {
+	readonly value: any;
+	readonly default?: T;
+	readonly type?: (value: any) => T;
+	readonly required: boolean;
+}
+
+export interface Logger {
+	debug: (...value: any) => void;
+	error: (...value: any) => void;
+	info: (...value: any) => void;
+}
diff --git a/src/util.ts b/src/util.ts
index c6a3228..4052ceb 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -2,12 +2,7 @@ import { Request } from 'express';
 import { OpenAI } from 'openai';
 import { appConfig } from './config';
 import { ValidationError } from './error';
-
-export interface CacheType {
-	set(key: string, value: string): void;
-	get(key: string): string | null;
-	clear(key: string): void;
-}
+import { CacheType, ConfigItem, Logger, OpenAIServiceType } from './types';
 
 function Cache(): CacheType {
 	const cache: { [key: string]: string | null } = {};
@@ -27,7 +22,7 @@ function Cache(): CacheType {
 
 export const cache = Cache();
 
-export const logger = {
+export const logger: Logger = {
 	debug: (...value: any) => {
 		const timestamp = new Date().toLocaleString();
 		console.debug(`\x1b[33m 🐛 ${timestamp}`, ...value, '\x1b[0m');
@@ -50,13 +45,6 @@ export function extractDomain(req: Request): string {
 	return url;
 }
 
-export interface ConfigItem<T> {
-	readonly value: any;
-	readonly default?: T;
-	readonly type?: (value: any) => T;
-	readonly required: boolean;
-}
-
 export function validateConfig<T extends Record<string, ConfigItem<any>>>(
 	config: T,
 ): Readonly<{ [K in keyof T]: T[K]['type'] extends (value: any) => infer R ? R : T[K]['value'] }> {
@@ -111,11 +99,6 @@ export function getIpAddress(req: Request): string {
 	return clientIp;
 }
 
-export interface OpenAIServiceType {
-	openai: OpenAI;
-	generateCommitMessage(diff: string): Promise<string | null>;
-}
-
 /**
  * Reference
  *