Age Inspect

What does this tool do?

Parse the Age header and show how long the response has been sitting in a shared cache (CDN/proxy), in seconds.

Useful to quickly tell whether you’re hitting cache and how stale-ish the response might be.

Age basics

• Age indicates seconds since the response was stored in a shared cache.
• It’s commonly added by CDNs/shared proxies.
• Age=0 doesn’t always mean “origin fresh”; it can simply be 0 seconds at that moment (interpret as a hint).

Why check it with Cache-Control

Age is a rough “how old” signal; whether that age is acceptable depends on Cache-Control (max-age/s-maxage, etc.).

• Age keeps rising and content never updates: suspect s-maxage/max-age/immutable
• Age always 0: not cached, bypassed, or revalidated each time

How to read Age (relation to freshness)

Age is “seconds since stored”. Fresh/stale is decided by Cache-Control (max-age / s-maxage, etc.) or Expires. A large Age is not automatically stale—compare it to the allowed lifetime.

• With s-maxage=600 and Age=120 → likely still fresh
• With s-maxage=600 and Age=1200 → likely stale (revalidation/refetch may occur)
• If max-age is short but Age is large, check 304/ETag/Last-Modified to see whether it’s being revalidated

HIT/MISS vs Age (clarify the difference)

Many CDNs expose proprietary HIT/MISS headers (e.g., X-Cache, CF-Cache-Status). Age is a more standard hint and is not the same thing—but using both can strengthen your inference.

• Age increases + HIT → likely served from shared cache
• Age=0 + repeated MISS → suspect bypass/not cached/fragmentation (Vary)
• Age=0 can still appear with HIT (timing, immediately after revalidation, etc.)

Syntax (how to read)

Age is an integer number of seconds, typically shown as Age: 123 in response headers.

• Age: 0
• Age: 42
• Age: 86400

Glossary (terms used on this page)

• Shared cache: a cache shared by many users (CDN/proxy).
• Freshness lifetime: how long a response is considered fresh (max-age/s-maxage/Expires, etc.).
• Revalidation: checking before reuse of stale entries (ETag/Last-Modified).

Examples (how to interpret)

• Age: 5 → likely recently cached (could be a hit)
• Age: 3600 → entry has lived ~1h (s-maxage might be large)
• Repeated Age: 0 → suspect bypass/no caching/revalidation or cache fragmentation (Vary)

Common pitfalls

• Age is a hint, not absolute truth (implementations and revalidation can affect it)
• Age may not reflect browser cache (mainly relevant for shared caches)
• Some CDNs hide/overwrite Age

Common issues behind CDN/proxies

Age is set by intermediaries, so it can differ by path (POP/layer). If you need ground truth, compare against a known origin-bypass path.

• Different POPs can yield different Age (resets) for the same URL
• During revalidation (304), Age may still increase/reset depending on implementation
• Transforms (compression/optimization) or cache-key rules can create separate entries (Vary)

stale-while-revalidate and Age

With Cache-Control directives like stale-while-revalidate / stale-if-error, caches may serve stale responses while updating in the background. In that case, a large Age can be expected.

Whether “served stale” is a problem depends on your design tolerance and freshness requirements.

Debugging workflow (recommended)

• Paste response headers into Response Headers Parser and check Age/Cache-Control/Date
• Use this tool to read Age (and optionally Date) and observe increase/fixed/reset patterns
• Check Vary Inspect for cache fragmentation (too many variants)

Troubleshooting checklist by symptom

• Caching not working: Age always 0, Cache-Control private/no-store/no-cache, Vary: *, etc.
• Updates not reflected: large Age, large s-maxage/max-age, immutable; check purge/bypass operations
• Unstable CORS: if Origin varies dynamically, verify Vary: Origin to prevent mixing

How to test (curl)

Hit the same URL multiple times and observe Age changes to infer caching (replace the URL).

• curl -I https://example.com/asset.js
• Check Age/Cache-Control/Date and paste into this tool for clarity

Related tools

• Cache-Control Inspect
• Expires Inspect
• ETag Inspect / Last-Modified Inspect
• Vary Inspect
• Response Headers Parser

Recommendations (practical)

• Age reflects CDN/proxy; interpret with Cache-Control
• Check public/private for shared cache eligibility
• Unexpected Age jumps may indicate intermediaries

What this tool does

• Extract and display Age as seconds
• Validate if Age is numeric
• Extract Age/Date from full response headers
• Estimate “stored-at” time from Age and Date

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)
• RFC 9111 (HTTP Caching)
• MDN: Age

FAQ

References

1. RFC 9110
2. RFC 9111
3. MDN: Age
4. MDN: HTTP caching

Next to view (diagnostic order)

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

1. If-Modified-Since Inspect — Parse If-Modified-Since and inspect conditional retrieval
2. Expires Inspect — Parse Expires and Date to inspect freshness behavior
3. If-None-Match Inspect — Parse If-None-Match and inspect revalidation conditions
4. Last-Modified Inspect — Parse Last-Modified and If-Modified-Since
5. Cache Not Working Troubleshooting — Troubleshoot cache-not-working symptoms step by step from headers
6. HTTP Cache Mismatch — Identify root causes of cache mismatches
7. Cache Response Analyzer — Judge cacheability from response headers
8. Cache Key Inspect — Visualize cache-key splits from URL, Vary, and headers

Same-theme links

Cache Control

Diagnose delivery policy across Cache-Control/Expires/Age

• Cache Not Working Troubleshooting — Troubleshoot cache-not-working symptoms step by step from headers
• HTTP Cache Mismatch — Identify root causes of cache mismatches
• Cache Response Analyzer — Judge cacheability from response headers
• Cache Key Inspect — Visualize cache-key splits from URL, Vary, and headers
• Cache Diagnostic — Run cross-header diagnostics for HTTP caching
• Cache Control Overview — Summarize how to use Cache-Control/Pragma/Expires together
• Cache-Control Inspect — Parse and interpret Cache-Control directives
• Pragma Cache Inspect — Parse Pragma and inspect legacy cache control behavior
• Expires Inspect — Parse Expires and Date to inspect freshness behavior