Topic Cluster

HTTP Performance

Caching, compression, connection behavior, and practical latency optimization topics.

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HTTP Status Codes
103 Early Hints
The server sends preliminary response headers to help the client start preloading resources. Learn how 103 Early Hints improves page load performance.
HTTP Status Codes
206 Partial Content: Range Requests Explained
206 Partial Content returns only the byte range requested. See a curl transcript, Content-Range, If-Range, video seeking and resumable downloads.
HTTP Status Codes
226 IM Used: HTTP Delta Encoding
226 IM Used is the response to a delta-encoded request under RFC 3229. See the A-IM and IM headers, how it works, and why almost nothing implements it.
HTTP Status Codes
304 Not Modified
Cached response is still valid. Learn how 304 Not Modified improves performance through conditional requests and caching.
HTTP Status Codes
HTTP 429 Too Many Requests: Causes, Retry-After and Fixes
Fix HTTP 429 Too Many Requests: read Retry-After and RateLimit headers, back off with jitter, and set up express-rate-limit v7, nginx limit_req and Cloudflare.
HTTP Headers
Accept-Encoding Header
Learn how Accept-Encoding tells servers which compression formats (gzip, br, deflate) your client supports to reduce bandwidth and speed up page loads.
HTTP Headers
Accept-Ranges Header
Learn how the Accept-Ranges header tells clients whether your server supports partial content requests (byte ranges) for efficient downloads and streaming.
HTTP Headers
Access-Control-Max-Age Header
Learn how Access-Control-Max-Age specifies how long browsers can cache CORS preflight results. Reduce preflight requests and improve cross-origin performance.
HTTP Headers
Age Header
Learn how the Age header indicates how long a response has been cached in seconds. Understand cache freshness calculations and CDN behavior.
HTTP Headers
Alt-Svc Header: How Browsers Discover HTTP/3
Alt-Svc advertises an alternative protocol for an origin. How h3=":443"; ma=86400 moves browsers to HTTP/3, what clear does, and how HTTPS DNS records differ.
HTTP Headers
Cache-Control Header: Directives, Examples and CDN Behavior
Cache-Control directives explained: max-age, no-cache vs no-store, s-maxage, stale-while-revalidate, immutable, with nginx, Cloudflare and Next.js examples.
HTTP Headers
Content-Encoding
Learn how Content-Encoding specifies compression algorithms (gzip, br, deflate) used to encode response bodies. Reduce bandwidth and improve load times.
HTTP Headers
Content-Range Header
Learn how the Content-Range header indicates which portion of a resource is being sent in partial content (206) responses for range requests and streaming.
HTTP Headers
Early-Hints
Learn how 103 Early Hints allows servers to send preload hints while preparing the main response. Improve page load performance with early resource loading.
HTTP Headers
ETag Header: Strong vs Weak, If-None-Match and 304 Debugging
ETag identifies a resource version for cache validation and optimistic locking. Strong vs weak ETags, If-None-Match, If-Match, and why nginx gzip weakens them.
HTTP Headers
Expires Header
Learn how the Expires header specifies when cached responses become stale. Understand date formats and when to use Expires vs Cache-Control for caching.
HTTP Headers
If-Match Header
Learn how the If-Match header makes requests conditional based on ETag matching. Prevent conflicts and lost updates in concurrent editing scenarios.
HTTP Headers
If-Modified-Since Header
Learn how the If-Modified-Since header requests resources only if modified since a specific date. Reduce bandwidth with efficient conditional caching.
HTTP Headers
If-None-Match Header
Learn how the If-None-Match header makes conditional requests using ETags. Avoid downloading unchanged resources and reduce bandwidth with cache validation.
HTTP Headers
If-Range Header
Learn how the If-Range header requests partial content only if the resource is unchanged. Efficiently resume downloads without re-fetching entire files.
HTTP Headers
If-Unmodified-Since Header
Learn how the If-Unmodified-Since header makes requests conditional on resources not being modified. Prevent conflicts in concurrent update scenarios.
HTTP Headers
Keep-Alive Header
Learn how the Keep-Alive header controls HTTP connection persistence and reuse. Reduce latency and improve performance by avoiding repeated TCP handshakes.
HTTP Headers
Last-Modified
Learn how the Last-Modified header indicates when a resource was last changed. Enable efficient cache validation with If-Modified-Since conditional requests.
HTTP Headers
Link Header
Learn how the Link header provides resource hints and enables preloading of CSS, fonts, and scripts to improve page load performance and user experience.
HTTP Headers
Performance-Timing: Server-Timing, Timing-Allow-Origin and Performance APIs
There is no Performance-Timing HTTP header. Use Server-Timing, Timing-Allow-Origin, the Navigation and Resource Timing APIs, TTFB and INP instead.
HTTP Headers
Range Header
Learn how the Range header requests partial content from servers to enable resumable downloads, video streaming, and efficient large file transfers.
HTTP Headers
Server-Timing Header
Learn how the Server-Timing header communicates server-side performance metrics to browsers. Analyze backend timing, database queries, and optimize performance.
HTTP Headers
Timing-Allow-Origin
Learn how the Timing-Allow-Origin header specifies which origins can access Resource Timing API data. Enable cross-origin performance monitoring securely.
HTTP Headers
Vary Header: Cache Keys, Vary: Origin and Accept-Encoding
Vary lists the request headers a response depends on, so caches keep separate copies. Vary: Accept-Encoding, Vary: Origin for CORS, Vary: *, and CDN cache keys.
HTTP Headers
X-Cache Header
Learn how the X-Cache header indicates cache hit or miss status from CDNs and proxies. Debug caching issues and verify CDN configuration with this header.
HTTP Headers
X-Response-Time
Learn how the X-Response-Time header indicates server processing time in milliseconds. Useful for performance monitoring and debugging slow requests.
Guides
API Rate Limiting: Algorithms, Headers and 429
Rate limit an HTTP API: fixed window, sliding window, token bucket and leaky bucket compared, plus 429, Retry-After, RateLimit headers, nginx and Express.
Guides
HTTP Compression: gzip, Brotli and Zstandard Setup
How HTTP compression works: Accept-Encoding negotiation, gzip vs Brotli vs zstd, nginx, Caddy, Express and Cloudflare config, BREACH, and measuring with curl.
Guides
HTTP Headers and Caching: A Practical Guide
Master HTTP caching with Cache-Control, ETag, Last-Modified, and conditional request headers. Learn how to optimize performance with proper cache strategies.
Guides
HTTP Range Requests: 206, Resume and Video Seeking
How HTTP range requests work: Range, Accept-Ranges, 206 and Content-Range, multipart/byteranges, 416, If-Range for safe resumes, and CDN and compression traps.
Guides
HTTP/3 and QUIC Explained: Setup, Fallback, 0-RTT
How HTTP/3 and QUIC work: UDP/443, connection IDs, 0-RTT replay risk, Alt-Svc and HTTPS DNS record discovery, nginx/Caddy/Cloudflare setup, and curl checks.
Glossary
CDN (Content Delivery Network)
A CDN is a network of edge servers that cache and serve responses near users. See how cache hits show up in headers and what CDNs do not cache by default.
Glossary
Keep-Alive (Persistent Connections)
Keep-alive reuses one TCP connection for many HTTP requests. Learn the HTTP/1.1 default, idle timeout defaults in nginx and Node, and why mismatches cause 502s.
Glossary
TTFB (Time to First Byte)
TTFB is the time from starting a request until the first byte of the response arrives. Learn what it includes, how to measure it and what usually inflates it.
Debug Guides
CDN Not Caching: cf-cache-status DYNAMIC, BYPASS, MISS
CDN not caching? Read cf-cache-status DYNAMIC, BYPASS, MISS or X-Cache: Miss from cloudfront, then fix Set-Cookie, Cache-Control, Vary and cache keys.

103 Early Hints

206 Partial Content: Range Requests Explained

226 IM Used: HTTP Delta Encoding

304 Not Modified

HTTP 429 Too Many Requests: Causes, Retry-After and Fixes

Accept-Encoding Header

Accept-Ranges Header

Access-Control-Max-Age Header

Age Header

Alt-Svc Header: How Browsers Discover HTTP/3

Cache-Control Header: Directives, Examples and CDN Behavior

Content-Encoding

Content-Range Header

Early-Hints

ETag Header: Strong vs Weak, If-None-Match and 304 Debugging

Expires Header

If-Match Header

If-Modified-Since Header

If-None-Match Header

If-Range Header

If-Unmodified-Since Header

Keep-Alive Header

Last-Modified

Link Header

Performance-Timing: Server-Timing, Timing-Allow-Origin and Performance APIs

Range Header

Server-Timing Header

Timing-Allow-Origin

Vary Header: Cache Keys, Vary: Origin and Accept-Encoding

X-Cache Header

X-Response-Time

API Rate Limiting: Algorithms, Headers and 429

HTTP Compression: gzip, Brotli and Zstandard Setup

HTTP Headers and Caching: A Practical Guide

HTTP Range Requests: 206, Resume and Video Seeking

HTTP/3 and QUIC Explained: Setup, Fallback, 0-RTT

CDN (Content Delivery Network)

Keep-Alive (Persistent Connections)

TTFB (Time to First Byte)

CDN Not Caching: cf-cache-status DYNAMIC, BYPASS, MISS

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