Why do some URLs fail with a CORS error?

Browsers block reading cross-origin responses unless the target sends Access-Control-Allow-Origin. The request may still reach the server; you simply cannot inspect the body from this page.

Are redirects followed automatically?

Fetch follows redirects by default. You see the final status after redirects—use a known redirect URL to confirm 301 vs 302 behavior when headers are visible.

Is this a replacement for monitoring?

No. It is a manual diagnostic. Automated uptime checks need server-side probes or sanctioned API keys, not a single browser tab.

Briefly Digest

HTTP Status Code Checker

Ready.

Status codes and headers from the client edge

A CDN misconfiguration often surfaces as 403 to browsers but 200 to datacenter curl. Running the check from your own laptop reproduces the user-visible status and Server/Timing headers together.

Reading common statuses

200 means OK for GET; 204 is success without body. 301/302 relocate resources—verify Location targets HTTPS. 401 and 403 differ: missing auth versus forbidden despite credentials.

CORS as a diagnostic signal

A network failure versus CORS failure tells different stories. If OPTIONS preflight fails, API gateways may need allowed methods or headers updated even when Postman from your desktop works.

FAQ

Why do some URLs fail with a CORS error?: Browsers block reading cross-origin responses unless the target sends Access-Control-Allow-Origin. The request may still reach the server; you simply cannot inspect the body from this page.
Are redirects followed automatically?: Fetch follows redirects by default. You see the final status after redirects—use a known redirect URL to confirm 301 vs 302 behavior when headers are visible.
Is this a replacement for monitoring?: No. It is a manual diagnostic. Automated uptime checks need server-side probes or sanctioned API keys, not a single browser tab.

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