426 Upgrade Required
The server refuses the request on the current protocol and asks the client to upgrade.
What it means
HTTP 426 Upgrade Required means the server will not process the request over the protocol the client is using and requires a switch to a different one. The response includes an Upgrade header naming the protocol the client should move to — for instance, requiring a newer TLS version before it will continue.
When it happens
It happens when a server insists on a protocol the client is not yet using, such as rejecting an outdated TLS version and demanding an upgrade, or requiring a different application protocol for the endpoint.
How to fix it
- Upgrade the client to the protocol named in the Upgrade header.
- For a TLS-version requirement, update the client or library so it negotiates a supported version.
- Confirm the client and server agree on which protocols are acceptable.
SEO impact
Negative if it blocks crawlers. If a crawler cannot meet the required protocol, the page goes unindexed, though modern crawlers support current protocols, so this is uncommon.
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Related codes
The server could not understand the request due to malformed syntax.
401 UnauthorizedAuthentication is required and has failed or not been provided.
402 Payment RequiredA largely reserved code intended for payment-gated access to a resource.
403 ForbiddenThe server understood the request but refuses to authorize it.
404 Not FoundThe server could not find the requested resource.
405 Method Not AllowedThe HTTP method used is not supported for the requested resource.
Related guides
A plain-English primer on HTTP status codes for SEOs: what the 2xx, 3xx, 4xx, and 5xx families mean, which ones affect rankings, and the codes worth knowing.
How to find and fix broken linksA practical walkthrough for finding broken links on your site, working out why each one breaks, and fixing them so visitors and crawlers stop hitting dead ends.