Why is now an explicit input?

It keeps the calculation deterministic: identical input produces identical output.

When is S-Maxage used?

It takes precedence over max-age when shared cache is selected.

It verifies standard calculations. Check vendor directives and configuration separately.

Calculate HTTP response age and freshness with RFC 9111 directive precedence.

Derive current age from Date, Age, and request timing, then apply S-Maxage, max-age, or Expires for the selected cache type.

Headers and timestamps are calculated only in this browser. Nothing is sent anywhere.

Enter headers and timestamps to calculate.

1
Choose cache type
Select a browser/private cache or shared CDN/proxy cache.
2
Enter timing and headers
Provide request, response, evaluation times, and response headers.
3
Compare age and lifetime
Inspect current age, freshness lifetime, and validation requirements.

This covers explicit RFC 9111 freshness. It does not reproduce vendor directives, heuristic freshness, cache keys, or Vary selection.

Why is now an explicit input?: It keeps the calculation deterministic: identical input produces identical output.
When is S-Maxage used?: It takes precedence over max-age when shared cache is selected.
Will this exactly match my CDN?: It verifies standard calculations. Check vendor directives and configuration separately.