routes/web.php is intended for browser-facing routes. Laravel applies the web middleware group to these routes, which commonly provides session state, cookies, CSRF protection, and shared error handling needed by traditional server-rendered applications.

routes/api.php is intended for stateless API endpoints and receives the api middleware group. API routes are commonly prefixed with /api and normally return JSON rather than HTML. In a current Laravel application, the API route file and related configuration may be added through the API installation flow, so the project setup should be checked instead of assuming every new application already contains it.