Error 526: Invalid SSL Certificate (Cloudflare)
Updated Free mock REST & WebSocket APIs
Error 526 Invalid SSL Certificate — In Full (strict) mode, Cloudflare couldn't validate the origin's TLS certificate.
- Class
- 5xx Server Error
- Defined in
- Unofficial (Cloudflare)
- Official
- No — Cloudflare-specific
- Cacheable by default
- No (unless Cache-Control/Expires say so)
- Safe to retry
- Sometimes — idempotent requests only
Try it: get a real 526 response
Our test endpoint answers every request with 526 Invalid SSL Certificate.
curl -i https://mockfox.dev/api/status/526Use it in tests, health-check monitors or to see how your client handles a 526. Add ?delay=2000 to slow it down.
What does Error 526 mean?
The handshake worked but the origin certificate is expired, self-signed, issued for another hostname or missing its intermediate chain. Install a valid certificate (Let's Encrypt or a Cloudflare Origin CA certificate, which Cloudflare trusts) or downgrade the SSL mode to Full (non-strict) until it's fixed.
How to fix 526
- Visitors: This is a server-side problem — wait a moment and retry, or check the site's status page.
- Developers: Check application and proxy logs at the time of the error, verify upstream services are healthy, and alert on 5xx rates.
Example 526 response
HTTP/2 526 server: cloudflare cf-ray: 8d2f1a3b4c5d6e7f-AMS content-type: text/html; charset=UTF-8
5xx Server Error: The server failed to fulfill a valid request — usually temporary, or a server-side bug. See the full list of HTTP status codes.
Related status codes
- 525 SSL Handshake FailedCloudflare couldn't complete the TLS handshake with the origin server.
- 495 SSL Certificate Errornginx: the client presented an invalid TLS client certificate.
- 520 Web Server Returned an Unknown ErrorCloudflare got an empty, unknown or unexpected response from the origin server.
Related tools
Frequently asked questions
What does Error 526 Invalid SSL Certificate mean?
In Full (strict) mode, Cloudflare couldn't validate the origin's TLS certificate.
Is 526 a client or a server error?
526 is a 5xx code: the server failed to handle a request that may be perfectly valid. It's often temporary.
Is 526 an official HTTP status code?
No. It isn't in the IANA HTTP Status Code Registry; it's specific to Cloudflare. Generic HTTP clients treat it as an unknown 5xx status.
How can I test how my app handles a 526?
Call https://mockfox.dev/api/status/526 — it responds with 526 to any method, with CORS enabled. Add ?delay=2000 to simulate a slow response.