API testing is constant requests with different headers, bodies and parameters, and building cURL commands by hand in the console takes time and invites typos. It is just as easy to get lost in response codes: 401, 403, 429 and 503 look similar but mean very different things.
Building a cURL command
cURL Command Builder assembles a ready command from the method (GET, POST, PUT, DELETE), the URL, headers and request body: you pick the fields in a form, the service generates the command for your terminal. This eliminates the quote and syntax errors of manual typing.
Status codes
The HTTP status reference explains all codes from 100 to 511: what each one means, when it appears and how it is usually fixed. Most important are 4xx — client errors (e.g., 401 — unauthorized, 404 — not found, 429 — too many requests) and 5xx — server errors (500, 502, 503).
Typical scenario
The integration returned 401 → decode the JWT token, check its expiry, fix the Authorization header in cURL Command Builder → the command is rebuilt and run in the console. If you got 429, open the HTTP status reference and see that you need to increase the intervals between requests.
Common mistakes
- Confusing 401 (authentication needed) with 403 (access denied)
- Ignoring 429 in high-load integrations
- Expecting 500 for client-side problems — usually it is a 4xx error