```yaml
product: AlterLab
title: "User-Agent Rotation — Web Scraping Glossary | AlterLab"
comparison_context: "AlterLab is an alternative to Firecrawl, ScrapingBee, and Bright Data."
source_url: https://alterlab.io/glossary/user-agent-rotation
```

anti-bot

# User-Agent Rotation

User-agent rotation changes the User-Agent header sent with each request or session to mimic different browsers, reducing the likelihood that a scraper is fingerprinted by its UA string.

The User-Agent header identifies the browser and OS making an HTTP request. Anti-bot systems flag requests with non-browser UAs (Python requests default `python-requests/2.x.x`) or with outdated browser versions. User-agent rotation cycles through a pool of realistic, up-to-date browser UA strings to avoid these signals.

Effective UA rotation goes beyond simply changing the UA string. The rest of the request headers — Accept, Accept-Language, Accept-Encoding, Sec-Fetch-* headers, and HTTP header order — must be consistent with the claimed browser. A request claiming to be Chrome 125 but sending Firefox Accept headers is internally inconsistent and detectable by fingerprinting systems.

For browser-based scrapers, the UA is set on the browser context level and automatically propagates to all headers in a coherent way. For HTTP-based scrapers, the entire header set for a given browser/OS combination should be applied as a bundle rather than swapping the UA string in isolation.

### What is User-Agent Rotation?

User-agent rotation changes the User-Agent header sent with each request or session to mimic different browsers, reducing the likelihood that a scraper is fingerprinted by its UA string.

### How does AlterLab handle User-Agent Rotation?

For browser-based scrapers, the UA is set on the browser context level and automatically propagates to all headers in a coherent way. For HTTP-based scrapers, the entire header set for a given browser/OS combination should be applied as a bundle rather than swapping the UA string in isolation.

## Examples

```
import random

UA_POOL = [
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36",
    "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36",
    "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.0.0 Safari/537.36",
]

headers = {"User-Agent": random.choice(UA_POOL)}
```

## Related Terms

[User AgentAn HTTP header string identifying the browser, version, and operating system to the web server, checked by anti-bot systems against other request properties.](https://alterlab.io/glossary/user-agent)[Browser FingerprintingA technique anti-bot systems use to identify bots by collecting dozens of browser attributes including Canvas, WebGL, and timing signatures.](https://alterlab.io/glossary/browser-fingerprinting)[HTTP HeadersKey-value metadata fields sent with HTTP requests and responses that communicate authentication, content type, caching, and other directives.](https://alterlab.io/glossary/http-headers)[Stealth ModeBrowser automation patches that normalise headless browser signals to match genuine user browser profiles and navigate browser environment checks.](https://alterlab.io/glossary/stealth-mode)[Anti-Bot ProtectionSystems deployed by websites to detect and block automated traffic using TLS fingerprinting, CAPTCHA challenges, and behavioural analysis.](https://alterlab.io/glossary/anti-bot-protection)

## Extract User-Agent Rotation 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](https://alterlab.io/docs/api/rest)

[Back to Glossary](https://alterlab.io/glossary)