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Browser Caching

/ˈbraʊzər ˈkæʃɪŋ/n.

Filed underPerformanceInfrastructure

In brief · quick answer

Storing previously downloaded resources on the user's device so subsequent page loads (or return visits) can skip network requests entirely.

§ 1 Definition

Browser caching stores HTTP responses locally on the user's device based on Cache-Control and ETag/Last-Modified headers. Well-cached resources eliminate HTTP requests entirely on repeat visits (cache hit) or validate with a lightweight 304 Not Modified response. Effective browser caching is the difference between a 300 ms page load and a 3 second one on return visits.

§ 2 Cache Headers

Cache-Control: max-age (seconds until stale), immutable (never re-validate), no-cache (always re-validate), no-store (never cache). ETag provides a content fingerprint for conditional revalidation. Last-Modified provides a timestamp-based fallback. For versioned assets (content-hashed filenames), use max-age=31536000 and immutable.

§ 3 Common Misunderstandings

Back/forward cache (bfcache) is NOT the same as HTTP cache. bfcache stores the entire page state (JS heap included) in memory for instant back/forward navigation. HTTP cache stores individual resources on disk. Both matter, but they serve different scenarios. Also, private browsing mode still uses in-memory caching but typically reduces cache duration.

§ 4 Optimization Tips

Version all static assets with content hashes. Set max-age to 1 year for versioned assets with the immutable directive. Use no-cache for HTML pages to ensure freshness while benefiting from conditional revalidation. Use ETags for validation. Avoid no-store unless the content contains sensitive data (bank transactions). Preload cacheable resources in the <head>.

§ 5 Note

Browser storage is limited per origin (typically 10-50 MB for disk cache). Safari and Chrome have different eviction policies. Service Workers can augment browser caching with programmatic control via the Cache Storage API.

§ 6 In code

# Versioned CSS/JS: cache forever
Cache-Control: public, max-age=31536000, immutable

# HTML: always revalidate but can use ETag
Cache-Control: public, no-cache
ETag: "abc123"

§ 7 Common questions

Q. Is browser cache cleared when the user clears history?: A. Yes. Browser cache is typically cleared alongside browsing data. Service Worker caches are sometimes preserved separately.

Key takeaways

Stores resources on the user's device.
Cache-Control headers govern behavior.
Use content hashes for long-lived caching.
Return visitors benefit most.

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# Browser Caching

Storing previously downloaded resources on the user's device so subsequent page loads (or return visits) can skip network requests entirely.

Category: Performance (also: Infrastructure)

Author: Atomic Glue Performance Team

## Definition

## Cache Headers

## Common Misunderstandings

## Optimization Tips

## Note

## In code

# Versioned CSS/JS: cache forever
Cache-Control: public, max-age=31536000, immutable

# HTML: always revalidate but can use ETag
Cache-Control: public, no-cache
ETag: "abc123"

## Common questions

Q: Is browser cache cleared when the user clears history?

A: Yes. Browser cache is typically cleared alongside browsing data. Service Worker caches are sometimes preserved separately.

## Key takeaways

Stores resources on the user's device.
Cache-Control headers govern behavior.
Use content hashes for long-lived caching.
Return visitors benefit most.

## Related entries

Last updated July 2026. Permalink: atomicglue.co/glossary/browser-caching