If-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-Match or Request Headers and click “Parse”. It lists ETags and strong/weak flags.

Notes (this tool)

  • Accepts If-Match: header lines (multi-line paste is OK).
  • * means “any match”.

About this page

What does this tool do?

Split If-Match to list ETags (strong/weak).

Useful for diagnosing update conflicts (412 Precondition Failed).

Basics (role of If-Match)

  • If-Match executes only if the ETag matches.
  • If the condition fails, 412 may be returned.
  • Be aware of strong vs weak ETags.

Input examples

  • If-Match: "abc123"
  • If-Match: W/"abc123", "def456"
  • If-Match: *

Common pitfalls

  • ETag changes causing repeated 412s
  • Misunderstanding the meaning of *
  • Using weak ETag with If-Match

Debugging workflow (recommended)

  • Check ETag with ETag Inspect
  • Parse If-Match here
  • Check if used with If-Unmodified-Since
  • ETag Inspect
  • If-None-Match Inspect
  • If-Unmodified-Since Inspect

Recommendations (practical)

  • Use If-Match for updates (PUT/DELETE)
  • Keep ETag current to avoid write conflicts
  • Weak ETags are not ideal for update preconditions

What this tool does

  • List If-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-Match

FAQ

Difference between If-Match and If-None-Match?

If-Match prevents update conflicts; If-None-Match is for cache validation.

References

  1. RFC 9110
  2. MDN: If-Match

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

  1. ETag Builder — Build ETag values for testing and operations
  2. Cache Validator Overview — Summarize relationships among ETag/Last-Modified validators
  3. ETag Policy Checker — Check ETag operational policy consistency
  4. If-Unmodified-Since Inspect — Parse If-Unmodified-Since and inspect precondition behavior
  5. ETag Inspect — Parse ETag and If-None-Match consistency
  6. If-None-Match Inspect — Parse If-None-Match and inspect revalidation conditions
  7. If-Modified-Since Inspect — Parse If-Modified-Since and inspect conditional retrieval
  8. Last-Modified Inspect — Parse Last-Modified and If-Modified-Since

Cache Validators

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