CORS Inspector

Cross-Origin Diagnostic Panel

Simulate preflight and actual requests server-side to quickly identify whether the issue is with Allow-Origin, Allow-Headers, or credentials.

Simulate CredentialsUsed for checking scenarios that require credentials like Cookies or Authorization.

Troubleshoot cross-origin errors online, find which step didn't match first.

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Use Cases

When browser reports CORS errors, run a check here with target URL and Origin first
Verify cross-origin configuration is working correctly during frontend-backend integration and view overall assessment
Enable credentials option to test why cookies or custom headers are being blocked
Check Nginx reverse proxy or API gateway cross-origin rule configuration with item-by-item results and fix suggestions

Features

No more guessing cross-origin errors: Preflight failures, credential conflicts, and header mismatches shown directly
Granular issue location: Separate preflight and actual requests, see exactly which one fails
Suitable for integration and gateway scenarios: Frontend, backend, Nginx, and API gateway teams can troubleshoot together
Results easier to share: Structured output ready to send directly to API providers or ops for collaborative handling

How to Use

1.Enter target API URL, source Origin, request method, and custom request header list
2.Check whether to simulate credentials (credentials), click Start Check button
3.View overall assessment: whether preflight is required, whether preflight passed, whether actual response is readable
4.Check each CORS header status and detailed explanation in item-by-item checks, adjust configuration according to fix suggestions

FAQ

Browser shows cross-origin error, what should I check first?

Priority check Allow-Origin, Allow-Methods, Allow-Headers, and Credentials match your actual request. Many cross-origin issues get stuck here.

Why does the actual request fail even after preflight passes?

Common causes include incomplete response headers, credential configuration errors, or backend returning inconsistent results for different origins. This tool helps you separate preflight and actual request differences.

Is it suitable for troubleshooting cross-origin issues in frontend integration, gateway, and proxy layers?

Yes. Whether browser direct connection, Nginx reverse proxy, API gateway, or local development environment, you can use it to check if cross-origin configuration is effective.

Are check results helpful for resolving cross-origin errors?

Yes. The tool structures key information like allowed origins, allowed methods, and allowed request headers, making it easy to quickly locate which configuration is missing or conflicting.