The endpoint returns nothing but an error
You are wiring a fetch call and it either throws, returns 401, or — most often — fails with a CORS message before you ever see a response body. Guessing from the network tab wastes time. You want to reproduce the exact request and read the real result.
Build the request and watch it run
Open the API Request Builder. Set the method, paste the URL, add any headers (Authorization, Accept), pick a body format for POST/PUT, and send. You see the live status, round-trip time, response headers, and body — all from your browser.
Worked example
A GET https://api.github.com/zen returns 200 with a short body. Change it to a POST against your own API with a JSON body and watch the Content-Type header matter: a missing application/json often produces a 415.
Boundaries (important)
- A static site cannot bypass CORS for you. If the server does not return
Access-Control-Allow-Origin, the browser blocks the response regardless of what the tool shows. - For endpoints you do not own, send the request from your own backend or proxy, then compare against what the builder shows.
- The tool never stores your URL, headers, or body.
FAQ
Why do I get CORS even though the API works in Postman? Postman does not enforce browser CORS; the browser does. The fix is server-side — see the CORS Header Generator.
Can I send cookies? Yes, switch credentials, but then Allow-Origin must be your exact origin, not *.