ETag: Strong/weak identifiers for resource versions. | Last-Modified: Timestamp of last modification. | If-None-Match: Revalidate using ETag.

HTTP Caching Guide

Q: Cache-Control Directives

max-age: Freshness lifetime in seconds. | no-store: Do not store response at all. | no-cache: Store but revalidate before use.

Q: Example

Cache-Control: public, max-age=60, s-maxage=300, stale-while-revalidate=30 ETag: "v1-abc"

Cache-Control directives, validators, and practical caching flows.

Cache-Control Directives

Key / Code	Description
max-age	Freshness lifetime in seconds.
no-store	Do not store response at all.
no-cache	Store but revalidate before use.
public	Cacheable by shared caches/CDNs.
private	Cacheable only by the browser.
stale-while-revalidate	Serve stale while revalidating.

Validators

Key / Code	Description
ETag	Strong/weak identifiers for resource versions.
Last-Modified	Timestamp of last modification.
If-None-Match	Revalidate using ETag.
If-Modified-Since	Revalidate using Last-Modified.

Example

Cache-Control: public, max-age=60, s-maxage=300, stale-while-revalidate=30
ETag: "v1-abc"
Vary: Accept-Encoding

Common Caching Strategy

For HTML pages, keep browser freshness short and rely on validators. For versioned static assets, use a very long max-age with immutable file names. For API responses, decide whether the response is public or private first, then combine Cache-Control with ETag or Last-Modified so stale content can be revalidated cheaply.

Knowledge is power.