API foundations
Inspect requests and responses
Use curl to see methods, URLs, headers, bodies, and status codes instead of debugging an API from rendered JSON alone.
8 minute lesson
A browser tab hides most of an HTTP exchange. API debugging starts by inspecting the complete request and response.
curl -i includes response headers. -v shows connection and request details. Use -X only when necessary; a request body option such as --json already selects POST.
curl -i http://localhost:3000/books
curl -i --json '{"title":"Dune","author":"Frank Herbert"}' http://localhost:3000/booksRead the exchange in order: resolved URL, request method and headers, response status, response headers, then body. A JSON-looking body does not prove success; a proxy can return an HTML error, a redirect, or a cached response with a surprising status. Use -i for contract evidence and add -v when connection, TLS, redirect, or request-header details matter.
The browser network panel adds browser-specific evidence such as preflight requests and blocked response access. The server may have processed a request even when browser JavaScript reports a CORS failure. Reproduce the HTTP request with curl, then compare the browser’s Origin and preflight headers before changing application logic.
Send one valid request and one request to a missing path. Save the exact status, content type, and body for each.
Lesson completed