CORS Explainer
Interactive CORS scenario debugger
CORS Explainer: Interactive CORS scenario debugger. A free, browser-based tool from DevToolbox that runs entirely on your own device: no upload, no account, no tracking.
About the CORS Explainer
Free interactive CORS explainer tool. Understand preflight requests, required headers, and server configuration. Simulate CORS scenarios and get fix suggestions. It is one of the network & api tools on DevToolbox, and like all of them it runs entirely in your browser.
This is a reference and calculation tool, not a probe: the numbers and lookups are computed from tables and arithmetic in your browser rather than by contacting any host. That keeps it usable behind a firewall and means nothing about your network is disclosed.
What you can do with it
- CORS debugger
- Preflight request
- Access-Control-Allow-Origin
- CORS headers
- Fix CORS error
- Cross-origin resource sharing
How to use it
- Enter the address, code or identifier you want to look up.
- The breakdown is calculated locally from reference tables and arithmetic.
- Every derived field is shown together so you can check your working.
- Copy the result or share the link.
Questions
- Is my data uploaded anywhere?
- No. The tool is JavaScript that runs in the tab you already have open, and DevToolbox has no backend to send anything to. You can open the network tab and watch: after the page and its script load, nothing is sent while you work.
- Does it work offline?
- Once the page has loaded, yes. The tool needs no network access to do its job, so it keeps working if your connection drops. Reloading the page does need the network unless your browser has it cached.
- Is it free, and do I need an account?
- It is free and there is no account, no sign-in and no usage limit. There is nothing to register because there is no server keeping track of anything.
Related tools
The CORS Explainer sits in Network & API, one of the 90 tools on DevToolbox.