Basics

Create a Hono app, answer two routes with text and with JSON, and export it so the runtime can call its fetch(), the way Cloudflare Workers, Bun and Deno do.

Give the cats API its routes: a parameter in the path, two parameters, a route that must be registered before the parameterised one, and a DELETE that answers 204.

Read what a request carries, its query string, its headers and its JSON body, and shape the response: a status, a header, text or JSON depending on what the client accepts.

Run code around every handler: a middleware that tags each request with an id the handler can read, and one that guards the cats routes with an API key and answers 401 itself.

Check a JSON body, a path parameter and a query value before the handler runs, with Hono's validator, and answer 400 with a message that names the problem.

Throw HTTPException where a problem is found, and give the whole API one shape for errors with app.onError() and app.notFound(), including what a crash looks like from outside.

Keep state across requests the way a browser does: a session cookie set at login and read on every request, a preference cookie that outlives the session, and a logout that deletes one without touching the other.

Split the API into files, one Hono app per resource, mount them with app.route() and put the whole thing under a base path.

Answer before the whole body exists: a text export written line by line with streamText(), and a feed of server-sent events with streamSSE() that keeps the connection open.

Test the cats API without a server: build a fresh app per test, call it with app.request(), and prove the tests mean something by catching four bugs planted in the code.