Cache Validator Overview

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 headers and click “Parse”. It summarizes ETag/If-None-Match/Last-Modified/If-Modified-Since/If-Range relationships.

Notes (this tool)

  • When combining ETag and Last-Modified, unstable generation rules can make revalidation inconsistent.
  • If-Range applies only to partial responses and is evaluated differently from normal revalidation.

About this page

What does this tool do?

Organize ETag / Last-Modified and their validators (If-None-Match / If-Modified-Since / If-Range) in one view.

Gives a quick overview of 304 behavior and conditional Range validation.

Mappings (quick)

  • ETag ⇔ If-None-Match (cache validation)
  • Last-Modified ⇔ If-Modified-Since (date validation)
  • ETag/Last-Modified ⇔ If-Range (range condition)

Common statuses

  • 304 Not Modified: match, no body
  • 200 OK: changed or condition failed
  • 206 Partial Content: range condition met
  • 412 Precondition Failed: If-Unmodified-Since/If-Match failed

Debugging workflow (recommended)

  • Extract ETag/Last-Modified via Response Headers Parser
  • Check If-* in request headers
  • Summarize relationships with this tool

Recommendations by use case

  • API (JSON): always include ETag or Last-Modified
  • HTML: Last-Modified is often more stable than weak ETag
  • Range: align If-Range with ETag/Last-Modified
  • ETag Inspect
  • If-None-Match Inspect
  • If-Modified-Since Inspect
  • If-Range Inspect
  • If-Unmodified-Since Inspect

What this tool does

  • Summarize cache validator relationships
  • Show header presence and combinations

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: HTTP caching

FAQ

Do I need both ETag and Last-Modified?

Not mandatory, but having both often improves compatibility and revalidation quality.

When should If-Range be used?

Use it with Range requests when resuming partial transfer only if the resource is unchanged.

References

  1. RFC 9110
  2. MDN: HTTP caching

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

  1. If-Match Inspect — Parse If-Match and inspect update preconditions
  2. If-Unmodified-Since Inspect — Parse If-Unmodified-Since and inspect precondition behavior
  3. ETag Builder — Build ETag values for testing and operations
  4. If-None-Match Inspect — Parse If-None-Match and inspect revalidation conditions
  5. ETag Inspect — Parse ETag and If-None-Match consistency
  6. If-Modified-Since Inspect — Parse If-Modified-Since and inspect conditional retrieval
  7. Last-Modified Inspect — Parse Last-Modified and If-Modified-Since

Cache Validators

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