When a browser refuses a cross-origin request, serves a stale asset, or downloads a file it should have rendered, the answer is in the response headers.
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HTTP Headers Checker
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Free · API · MCPToolYour platform
Use HTTP Headers Checker three ways
The free HTTP Headers Checker on this page works in your browser. The same workflow is available via REST API for apps and via MCP for Cursor, Claude, and other agents — one API key, one plan, one quota. This tool is part of the developer-apis module under Developer Tools.
- Free in browserUse HTTP Headers Checker here — no account required.
- REST APICall from your server with
X-Api-Key. - MCP for agentsConnect Cursor or Claude to ToolYour MCP with the same key.
- 1. Get an API keySign in and open Dashboard → API Keys (works for REST and MCP).
- 2. Call or connectUse the REST API from your server, or paste the MCP URL into your agent config.
- 3. Same qualityOutput matches the free web tool across all three surfaces.
What is HTTP Headers Checker?
When a browser refuses a cross-origin request, serves a stale asset, or downloads a file it should have rendered, the answer is in the response headers. This HTTP headers checker fetches a public http or https URL with a GET request, follows redirects, and returns the complete header map alongside the status code and the final URL after any hops.
Scope is one URL per run with a twelve-second timeout — it does not crawl a site, replay custom request headers, or attempt anything behind authentication, and it can only reach publicly resolvable hosts. It also does not grade what it finds: there is no security score, no CSP analysis, and no pass or fail verdict. For graded CSP, HSTS, and permissions policy reports, Security Headers Analyzer under Security Tools is the right tool. Because this makes a live network call, it costs 3 credits rather than 1. To reproduce the same request locally, API Request Builder writes the cURL command.
Browser use is free and needs no signup. The same job runs over REST at GET https://api.toolyour.com/api/v1/developer-apis/http-headers-checker?url=… and over MCP at https://api.toolyour.com/mcp — one API key, one shared monthly credit pool, 3 credits per successful call.
What are common questions about HTTP Headers Checker?
Does it score security headers?
No. It returns the raw header map. For graded CSP, HSTS, and permissions policy analysis use Security Headers Analyzer under Security Tools.
Are redirects followed?
Yes. The response reports the final URL and status after redirects, which is how you spot an unexpected hop to a different host.
Why does this cost more credits?
It makes a live outbound network request rather than a local transform, so it costs 3 credits per call instead of 1.
Can it check a page behind a login?
No. Only publicly reachable URLs work — there is no way to supply cookies, tokens, or custom request headers.
What are the key features of HTTP Headers Checker?
Complete header map
Every response header returned as key and value, not a curated subset.
Redirects resolved
Reports the final URL and status so unexpected hops are visible.
Timeout protected
A twelve-second limit means a slow origin fails fast instead of hanging your script.
How do you use HTTP Headers Checker?
Enter a public URL
Use the exact URL the browser requested, including its query string.
Read the headers
Look at CORS, cache-control, and content-type first — most bugs live there.
Compare and fix
Change the origin configuration, then re-run to confirm the header changed.
The three headers behind most bugs
Access-Control-Allow-Origin — if it is missing, or echoes a different origin than the one making the request, the browser blocks the response after the server has already processed it. A request that succeeds in cURL and fails in the browser is nearly always this.
Cache-Control — a long max-age on a file with an unversioned name is why users still see yesterday's deploy. Check whether the header came from your application or from a CDN that rewrote it.
Content-Type — a JSON API sending text/plain, or an asset sent as application/octet-stream, changes how the browser handles the body entirely. The difference between rendering and downloading is usually this one header plus Content-Disposition.
Where header inspection fits
Use this tool for the raw truth about what an origin returns right now, including after a configuration change when you want confirmation rather than belief. Reproduce the exact same call locally with API Request Builder when you need to add authentication or a custom header this tool cannot send.
When the question shifts from "what is being sent" to "is what is being sent safe", move to Security Headers Analyzer under Security Tools, which grades CSP, HSTS, referrer policy, and frame options rather than just listing them.
Which HTTP / auth helper tools sit in this cluster?
Where do you browse more developer tools tools?
- Developer Tools tools
Browse the full Developer Tools category on ToolYour.
- Marketing Tools tools
Build UTM links, check ads copy limits, QA email subjects, and calculate ROAS/CPC/CTR — free in the browser; R
- Security Tools tools
Check HTTP security headers, TLS, cookies, JWTs, passwords, hashes, and SPF/DKIM/DMARC — free in the browser;
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