Which HTTP headers are most important for web scraping?
Several HTTP headers are crucial for successful web scraping and avoiding detection.
Critical headers:
1. User-Agent (most critical) Identifies your client as a browser and should match a real, recent browser string.
2. Accept Tells servers what content types you can process:
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
3. Accept-Language Specifies language preferences:
en-US,en;q=0.9
Helps you receive content in the desired language.
4. Accept-Encoding Tells servers you support compression (real browsers always do):
gzip, deflate, br
5. Referer Indicates which page you came from. Some sites:
- Require this header
- Block requests without it
- Block requests with suspicious referrers
6. Cookie Maintains session state across requests. Essential for:
- Authenticated scraping
- Sites that track sessions
- Multi-step workflows
7. Connection
Should typically be keep-alive for modern browsers.
8. Upgrade-Insecure-Requests
Set to 1 to tell servers you support HTTPS upgrades.
Special headers:
X-Requested-With
Set to XMLHttpRequest to identify AJAX requests, which return different data than page loads.
Beyond individual headers:
Anti-bot systems check:
- Header order (browsers send headers in consistent sequences)
- Header combinations (certain headers always appear together)
- Missing expected headers
- Impossible combinations
Implementation approaches:
Headless browsers (easier): Libraries like Puppeteer or Playwright automatically send correct headers with proper order and combinations.
Lightweight scrapers (more control):
Using requests, axios, or net/http requires manually constructing header sets that mimic real browsers.
Best practice: Copy headers from your actual browser using DevTools or our HTTP Request Analyzer as a reference, then replicate the entire header set in your scraper.