Client error · HTTP reference

426Upgrade Required

The server requires a different protocol to fulfil the request.

The company behind the code.

For software upgrades and modern protocols.

The server requires a different protocol to fulfil the request.

Available

Your logo, your message, your corner of the internet.

Returns this HTTP status with the current sponsor’s name, advertising message and website. Useful for testing how your app handles a response.

This is an independent project. Sponsorship does not confer ownership of HTTP standards.

Client error responses explain why a request could not be fulfilled.

Check the URL, method, authentication and request content. Repeating the same request without addressing the cause may produce the same response.

Reference reviewed 5 September 2026. How we use sources.