topic
Verified 2026-09-18

HTTP/3 Error Codes

HTTP/3 error codes describe stream, connection, and request failures over QUIC.

Preserve the distinction between H3_REQUEST_CANCELLED, H3_REQUEST_REJECTED, and connection errors. Retry only when the operation and server contract make retry safe, and translate to an HTTP response only when the request reached application processing.

httpprotocolhttp3quicerrors

Reference (http)

HTTP/3: H3_REQUEST_CANCELLED
QUIC: CONNECTION_REFUSED

Preserve the distinction between H3_REQUEST_CANCELLED, H3_REQUEST_REJECTED, and connection errors. Retry only when the operation and server contract make retry safe, and translate to an HTTP response only when the request reached application processing.

Common mistakes

  • Retrying every QUIC failure as if it were a 503, or leaking transport error details into a public API contract.

Related

HTTP/3 and QUIC ControlsHTTP 425 Too EarlyHTTP 503 Service Unavailable

Sources

Permalink: https://merginit.com/reference/http/http3-error-codes