ETag Builder
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
Enter an ETag value and Build. You can copy the ETag header string.
Notes (this tool)
- The value is wrapped in double quotes automatically.
About this page
What does this tool do?
Generate ETag strings and toggle W/ (weak).
Useful for testing cache validation with If-None-Match / If-Match.
Basics (role of ETag)
- ETag is a version identifier for a resource.
- Used with If-None-Match / If-Match for conditional requests.
- W/ indicates weak comparison (semantic equivalence).
Input examples
- Value: abc123 → ETag: "abc123"
- Weak ON → ETag: W/"abc123"
Common pitfalls
- ETag changes every time; 304 never hits
- Misusing weak/strong
Debugging workflow (recommended)
- Build ETag with this tool
- Check conditions with If-None-Match / If-Match
- Verify 304/412 via HTTP Status Inspect
Related tools
- ETag Inspect
- If-None-Match Inspect
- If-Match Inspect
What this tool does
- Build ETag strings
- Toggle weak/strong
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: ETag
FAQ
How should weak and strong ETags be chosen?
Use strong for byte-level identity and weak when semantic equivalence is sufficient.
Why is changing ETag on every response problematic?
It breaks 304 revalidation efficiency and increases bandwidth and latency costs.
References
Next to view (diagnostic order)
These links are generated from site_map rules in recommended diagnostic order.
- ETag Policy Checker — Check ETag operational policy consistency
- If-Match Inspect — Parse If-Match and inspect update preconditions
- Pragma Cache Inspect — Parse Pragma and inspect legacy cache control behavior
- Cache Validator Overview — Summarize relationships among ETag/Last-Modified validators
- ETag Inspect — Parse ETag and If-None-Match consistency
- If-None-Match Inspect — Parse If-None-Match and inspect revalidation conditions
- If-Modified-Since Inspect — Parse If-Modified-Since and inspect conditional retrieval
- If-Unmodified-Since Inspect — Parse If-Unmodified-Since and inspect precondition behavior
Same-theme links
Cache Validators
Connect ETag/Last-Modified and If-* to judge revalidation flow
- Cache Validator Overview — Summarize relationships among ETag/Last-Modified validators
- ETag Inspect — Parse ETag and If-None-Match consistency
- If-None-Match Inspect — Parse If-None-Match and inspect revalidation conditions
- If-Match Inspect — Parse If-Match and inspect update preconditions
- If-Modified-Since Inspect — Parse If-Modified-Since and inspect conditional retrieval
- If-Unmodified-Since Inspect — Parse If-Unmodified-Since and inspect precondition behavior
- Last-Modified Inspect — Parse Last-Modified and If-Modified-Since