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CORS header checker

Check CORS preflight and read-response headers for a URL, Origin, method, and custom request headers without sending write requests.

InputEnter a value to inspect

工具只发送 OPTIONS 预检和 HEAD/GET 读取请求，不会发送 POST/PUT/DELETE 写入请求。

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The result will appear here as structured cards.

Example results you can open

Short, high-intent examples that are easy to open, share, and understand for search engines and AI systems.

CORS baseline

Check default CORS behavior for a public URL

Inspect Access-Control-Allow-Origin, allowed methods, and preflight response clues.

Open example
Preflight check

Review CORS preflight behavior on a tool page

Validate preflight response, Vary behavior, and credential-related hints in a common scenario.

Open example

FAQ

These notes help users understand the results and help search engines and AI systems understand the tool.

What does CORS header checker do?

It helps you inspect or process this value and get a readable result quickly.

Is my input saved?

Local tools run in the browser when possible. Server-side checks only use the input needed to complete the lookup.

Why can CORS look allowed in the tool but still fail in the browser?

Browser behavior also depends on credential mode, third-party cookie policy, preflight cache, redirects, and fetch options. The tool diagnoses response headers, not full front-end runtime behavior.

What is risky about Access-Control-Allow-Origin: *?

It may be fine for fully public read APIs, but not for credentialed traffic. For cookies or auth, use explicit origin allowlists and `Vary: Origin`.

Related long-tail searches

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Related long-tail topics

These topics place this tool inside a fuller lookup workflow for search, AI citations, and sharing.

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