HTTP headers

What it does: asks a web address for its response and shows the status code, the response headers, and how long it took — without downloading the whole page. It's the quick "is this URL healthy, and what is the server telling me?" check.

What you need: a URL (e.g. https://example.com or an API endpoint).

Safe to run: yes — a single read-only request.

What to expect / reading results: the status code is the headline — 200 = OK; 301/302 = redirect; 401/403 = an auth problem (you're reaching it, but not allowed in); 404 = not found; 5xx = the server itself erred. That distinction is the fastest way to tell an API apart: "is it auth, or is it reachability?" (see the API use-case playbook). The headers show what the server runs, caching, and security settings.