425 Too Early (RFC 8470) is related to TLS 1.3 early data, also known as 0-RTT. A client that resumes a TLS session can send its first request together with the handshake, before the handshake is complete, to save a round trip. Early data can be replayed by an attacker, so it is only safe for requests without side effects.
A server that receives a request in early data and does not want to risk processing it can answer 425. The client must then automatically retry the request after the handshake has completed. CDNs and other intermediaries that forward early-data requests add the header Early-Data: 1, so the origin can answer 425 when a replay would be harmful.
Example response
HTTP/1.1 425 Too Early
Date: Fri, 06 Nov 2026 10:15:32 GMT
Content-Length: 0SEO and redirect checking
Browsers handle 425 automatically and users never see it. Crawlers and redirect checkers rarely use 0-RTT, so it has no practical SEO impact.
Common causes and use cases
- A resumed TLS 1.3 connection sent a
POSTas early data, and the server rejected it to prevent a replay. - An origin behind a CDN with 0-RTT enabled refuses requests marked
Early-Data: 1. - An application that cannot handle replays safely rejects all early data with 425.