ETag Policy Checker

Analyze cache-related headers across layers. No input is sent to a server. Use it for first-pass revalidation and CDN mismatch troubleshooting.

Status

Runs in your browser. No input is sent to a server. Use this as a first-pass diagnostic step.

How to use

Paste ETag or If-None-Match and click “Parse”. It shows weak ETags and multiple values.

Notes (this tool)

  • It cannot determine how ETags are generated.

About this page

What does this tool do?

Paste ETag / If-None-Match to check strong/weak ETags and policy alignment.

Quickly judge whether the policy matches update frequency and caching strategy.

Typical use cases

  • Review weak ETags (W/) usage
  • Decide whether ETag is necessary
  • Diagnose why If-None-Match is not effective

ETag policy basics

ETag identifies resource versions; strong ETags imply byte-for-byte identity while weak ETags imply semantic equivalence.

What this tool does

  • Parse ETag / If-None-Match
  • Detect weak ETags (W/)
  • Check multiple ETag values

Debugging workflow (recommended)

  • Paste response headers
  • Review Cache-Control, ETag, and Last-Modified
  • Trace 304/206/CDN differences with related inspectors

Operational notes

  • Cache behavior changes across browser, CDN, and proxy layers, so compare captures from the same observation point.
  • Header-only diagnosis may be insufficient. Also review application cache invalidation strategy and key design.

Referenced specs

  • RFC 9110 (HTTP Semantics: ETag)

FAQ

Is W/ prefixed ETag a problem?

It depends. Weak ETags are fine for semantic revalidation, but strict identity checks need strong ETags.

What should be checked when If-None-Match is ineffective?

Check whether ETag changes across delivery layers and whether clients actually send If-None-Match.

References

  1. RFC 9110 (HTTP Semantics)
  2. MDN: ETag

These links are generated from site_map rules in recommended diagnostic order.

  1. Pragma Cache Inspect — Parse Pragma and inspect legacy cache control behavior
  2. ETag Builder — Build ETag values for testing and operations
  3. If-Match Inspect — Parse If-Match and inspect update preconditions
  4. Cache Validator Overview — Summarize relationships among ETag/Last-Modified validators

Example

ETag: W/"abc123"
If-None-Match: "abc123", "def456"