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Cache validator

A cache validator is representation metadata a recipient can use in a conditional request.

Difficulty
beginner
Published
July 13, 2026
Last reviewed
Review due
  • caching
  • conditional requests

Definition

A validator is representation metadata used in conditional requests. Entity tags and modification dates are common validators, but they have different comparison rules and precision.

Why it matters

A recipient can send a stored validator with a later request. The server evaluates the condition against the selected representation and can avoid retransmitting content when the condition permits reuse.

ETag: "manual-v4"
If-None-Match: "manual-v4"

Expected result: the first field supplies an entity-tag validator on a response; the second presents that stored validator as a request condition. Their presence alone does not guarantee a 304 because the server evaluates the current selected representation.

  • Strong validator: suitable when equivalence requires the representation data to match according to the strong comparison rules.
  • Weak validator: useful when two representations are semantically equivalent even if their bytes are not identical.

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