If-None-Match Inspect

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 If-None-Match or Request Headers and click “Parse”. It lists ETags and weak/strong flags.

Notes (this tool)

  • Accepts If-None-Match: header lines (multi-line paste is OK).
  • * means “any match”.

About this page

What does this tool do?

Split If-None-Match to list ETags (weak/strong).

Useful for validating 304 Not Modified and cache conditions.

Basics (role of If-None-Match)

  • If-None-Match validates caches using ETags.
  • If it matches, 304 is returned; otherwise typically 200.
  • ETags can be strong or weak.

Input examples

  • If-None-Match: "abc123"
  • If-None-Match: W/"abc123", "def456"
  • If-None-Match: *

Weak vs strong

Weak means semantically equivalent; strong means byte-for-byte identical.

Common pitfalls

  • No ETag means If-None-Match is ineffective
  • ETag changes every time, causing 200 always
  • Misunderstanding the meaning of *

Debugging workflow (recommended)

  • Check ETag with ETag Inspect
  • Parse If-None-Match here
  • Check if Last-Modified is also used
  • ETag Inspect
  • Last-Modified Inspect
  • If-Modified-Since Inspect

Recommendations (practical)

  • Always pair with ETag
  • Use with Cache-Control: no-cache for revalidation
  • Consider If-Range when supporting Range

What this tool does

  • List If-None-Match tags with weak/strong flags
  • Handle * wildcard

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)
  • MDN: If-None-Match

FAQ

Which should I use: If-None-Match or If-Modified-Since?

If you can use ETags, If-None-Match is more precise.

References

  1. RFC 9110
  2. MDN: If-None-Match

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

  1. How to Diagnose Missing 304 Responses — Trace ETag/Last-Modified and If-* round trips to isolate missing 304 behavior
  2. If-Unmodified-Since Inspect — Parse If-Unmodified-Since and inspect precondition behavior
  3. If-Modified-Since Inspect — Parse If-Modified-Since and inspect conditional retrieval
  4. Cache Validator Overview — Summarize relationships among ETag/Last-Modified validators
  5. Age Inspect — Parse Age to estimate shared-cache residency time
  6. ETag Inspect — Parse ETag and If-None-Match consistency
  7. ETag Builder — Build ETag values for testing and operations
  8. If-Match Inspect — Parse If-Match and inspect update preconditions

Cache Validators

Connect ETag/Last-Modified and If-* to judge revalidation flow