How to use the Network panel to debug API and fetch issues
network panel, request inspection, response headers, status codes, payload inspection, CORS errors
The Network Panel Is a Debugger for HTTP
When a frontend feature misbehaves and the cause might be in the network layer, the Network panel in DevTools gives you complete visibility into every HTTP request -- headers, payload, status code, and response body -- without modifying any code.
Reading a Request
Open DevTools, go to the Network tab, then trigger the failing action. Click the failing request. The Headers tab shows request method, URL, status code, and both request and response headers. The Payload tab shows what your code sent. The Response tab shows what the server returned. Most API bugs are visible immediately in one of these three places.
// Common findings in the Network panel:
// Status 401: missing or expired auth token in request headers
// Status 400: malformed request body (check Payload tab)
// Status 404: wrong URL -- check the actual request URL, not the code
// Status 200 but wrong data: server logic issue, check response body
// Request missing: fetch call never executed, JS error before it ran
// CORS error: blocked before reaching server, check console
CORS Errors
CORS errors appear as blocked requests in the console, not in the Network panel normal flow. The fix is almost always on the server -- the server must send the correct Access-Control-Allow-Origin header. Changing the frontend does not fix CORS. Use the Network panel to confirm whether the server is sending the required headers.