CORS Checker Guide
Check whether a URL can be read from this browser origin and inspect visible CORS headers.
A short companion for CORS Checker: when it is useful, what it expects, and what to check before using the result.
What it does
Check whether a URL can be read by JavaScript from this site origin. The tool sends a browser fetch request and, where possible, an OPTIONS-style probe, then reports what the browser allowed the page to see. It cannot spoof arbitrary Origin headers because browsers deliberately do not allow that.
Use the tool
Open CORS Checker, add the input the tool asks for, run it, and check the output before using it elsewhere.
Input and output
- Input: text.
- Output: text.
- Category: Network.
Privacy and processing
This tool needs a network request to complete the lookup or test. Send only data you are comfortable sharing with the target service.
Questions
Why does it say blocked without showing the server headers?
When CORS blocks a response, the browser hides the response from JavaScript. That is the rule this tool is testing, so sometimes the only honest answer is that the page could not read the details.
Related guide
For broader background, see Debugging CORS Without Guessing.