FREE TOOLS
HTTP Cache Freshness Calculator
Calculate HTTP response age and explicit freshness from supplied clocks and cache headers.
Cache-Control, HTTP Date instant, Request instant, Response instant, Observation instant, Received Age seconds, Cache type, Expires instant (optional)
http-cache-freshness-calculator.json (complete report)
Browser only
Runs locally in your browser. Your files, pasted content and generated output are not uploaded. Reset clears this tool’s working data.
This tool needs JavaScript. If it does not load, refresh the page and try again.
How to use this tool
- Enter values using the examples, or choose a local file where requested. Follow the displayed supported input shapes and limits.
- Choose Calculate result and inspect the complete result.
- Download result to save the primary file. Where supplied, additional links save source files and the full JSON report. Reset restores examples and clears output.
Examples
Cache-Control: max-age=60
HTTP Date instant: 2026-10-23T00:00:00Z
Request instant: 2026-10-23T00:00:01Z
Response instant: 2026-10-23T00:00:03Z
Observation instant: 2026-10-23T00:00:13Z
Received Age seconds: 2
Cache type: private
Expires instant (optional):
Limitations
- RFC9111 supplied-clock age and explicit freshness. Support max-age,s-maxage,Expires,no-cache,no-store,private,public,must-revalidate,proxy-revalidate,immutable,must-understand,no-transform,stale-while-revalidate and stale-if-error. Stale-extension allowances are not applied. No heuristic lifetime; missing explicit lifetime is0. fresh describes age only; no-cache still requires revalidation and storageAllowed separately reflects no-store/shared private. ASCII Cache-Control up to65536 characters/100 directives; identical duplicates allowed,conflicting/unknown directives or field lists refuse. No remote/cache-state observation.
- Text fields are limited to100,000 UTF16 units each and400,000 combined UTF8 bytes; file fields have their own displayed limits. Combined output is at most4MiB. Processing stops after30 seconds; tool-specific bounds may be tighter.
- Generated source is a downloadable result and is not executed here. Inspection does not establish remote behavior, trust or standards certification.