HTTP Concepts

Conditional Request

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An HTTP request that includes conditions (If-Match, If-None-Match, If-Modified-Since) allowing the server to respond with 304 Not Modified if the resource hasn't changed.

Related Protocols

HTTP

Mentioned in Guides

HTTP Conditional Requests: If-Match, If-None-Match, and Beyond HTTP Fundamentals

Choosing the Right HTTP Status Codes for REST APIs API Design & Best Practices

RFC 9110: HTTP Semantics Deep Dive Protocol Deep Dives

Related Scenarios

409 Conflict — Optimistic Locking Failure HTTP

304 Not Modified — Cache Serving Stale Content HTTP

FAILED_PRECONDITION — Stale State in Distributed System gRPC

Defined In

RFC 9110 HTTP Semantics

RFC 9111 HTTP Caching

Decision Guides

Which HTTP Success Code Should I Return? Should I Cache This HTTP Response?

See Also

Range Request HTTP Concepts

Cache-Control Caching & Performance

ETag (Entity Tag) Caching & Performance

Last-Modified Caching & Performance

Conditional Headers Web Standards