protocol

HTTP Headers

Key-value metadata fields sent with HTTP requests and responses that communicate authentication, content type, caching, and other directives.

HTTP headers are key-value pairs transmitted at the start of every HTTP request and response that carry metadata about the message. Request headers tell the server about the client (User-Agent, Accept-Language, Accept-Encoding), the content being sent (Content-Type, Content-Length), authentication credentials (Authorization, X-API-Key), and caching preferences (If-None-Match, Cache-Control). Response headers tell the client about the server's response and how to handle it.

In web scraping, headers are a significant detection surface. Anti-bot systems validate that request headers match what a real browser would send for that specific browser version and operating system. A mismatch between the User-Agent claiming to be Chrome 124 on Windows and a missing `sec-ch-ua` client hint header, or a non-browser `Accept-Encoding` value, is a strong bot signal.

Critical headers to get right for anti-bot evasion: `User-Agent`, `Accept`, `Accept-Encoding`, `Accept-Language`, `sec-ch-ua`, `sec-ch-ua-mobile`, `sec-ch-ua-platform`, `Sec-Fetch-Site`, `Sec-Fetch-Mode`, `Sec-Fetch-Dest`. AlterLab manages the full header set automatically, matching the exact header profile of the Chromium version in use.

What is HTTP Headers?

Key-value metadata fields sent with HTTP requests and responses that communicate authentication, content type, caching, and other directives.

How does AlterLab handle HTTP Headers?

Critical headers to get right for anti-bot evasion: `User-Agent`, `Accept`, `Accept-Encoding`, `Accept-Language`, `sec-ch-ua`, `sec-ch-ua-mobile`, `sec-ch-ua-platform`, `Sec-Fetch-Site`, `Sec-Fetch-Mode`, `Sec-Fetch-Dest`. AlterLab manages the full header set automatically, matching the exact header profile of the Chromium version in use.

Examples

# Headers a real Chrome browser sends
GET /page HTTP/2
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36...
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.9
Accept-Encoding: gzip, deflate, br
sec-ch-ua: "Chromium";v="124", "Google Chrome";v="124"
Sec-Fetch-Site: none
Sec-Fetch-Mode: navigate

Related Terms

User Agent
An HTTP header string identifying the browser, version, and operating system to the web server, checked by anti-bot systems against other request properties.
TLS Fingerprint
A signature derived from TLS handshake parameters a client sends when opening an HTTPS connection, used by anti-bot systems to classify traffic.
Anti-Bot Protection
Systems deployed by websites to detect and block automated traffic using TLS fingerprinting, CAPTCHA challenges, and behavioural analysis.
REST API
A web service that exposes data and actions through standard HTTP methods and resource-oriented URLs, returning structured JSON responses.

Extract HTTP Headers data from any website

AlterLab returns clean, structured data from any public URL — no scraper infrastructure needed. Start free, no credit card required.

View API docs
Back to Glossary

Your first scrape.
Sixty seconds.

$1 free credit — up to 5,000 scrapes. No credit card.Just a POST request.

terminal
curl -X POST https://api.alterlab.io/v1/scrape \
-H "X-API-Key: YOUR_KEY" \
-H "Content-Type: application/json" \
-d '{"url": "https://example.com", "formats": ["markdown"]}'

No credit card required · $1 free credit, up to 5,000 scrapes · Balance never expires