demo · v142 · network

Cache Lifetime Calculator

Tune your compression dictionary TTL against your deployment cadence and user visit frequency. See exactly what fraction of visits will hit a fresh dictionary — and what the browser falls back to when it expires.

Presets:

Parameters

Slider = visits × 0.5

Results

Visits hitting expired dict —
Bytes saved per fresh visit —
Recommended TTL —
Dict still fresh at 30 days —
Avg visits served fresh —
Recommendation Adjust the sliders to see a recommendation.

30-day visit coverage timeline

Each row is one day. Green = dictionary still fresh for that day's visits. Red = expired — browser falls back to full response.

Dictionary fresh Dictionary expired

What happens when the dictionary expires?

  1. The browser cannot locate a fresh matching dictionary for the current URL. The Available-Dictionary request header is omitted.
  2. The server responds with the full (non-delta) compressed response — the same as if the feature did not exist. No 4xx error; purely a cache miss scenario.
  3. If the response includes a new Use-As-Dictionary header, the browser stores this response as the new baseline dictionary for future delta-compression.
  4. The next visit can again send Available-Dictionary, resuming delta compression. One cold visit per TTL expiry is the worst case.

Header snippet

Copy-paste the generated Use-As-Dictionary response header for your current TTL setting:

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See also