A user agent is an HTTP header string that identifies the client software making a request, including the browser name, version, operating system, and rendering engine. Servers use this information to tailor responses.
Every HTTP request includes a User-Agent header. A typical Chrome user agent looks like: "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36". Servers parse this string to determine the client type. Web scrapers set custom user agents to match real browsers and avoid detection.
Handle it deliberately in production scrapers -- most breakage traces back to skipping this step.
USER-country-de-session-task01Add this string to your scraper's proxy credentials and every request in the job shares one exit IP, which keeps user agent-related behavior consistent across the run. Change "task01" per worker to isolate parallel scrapes.
Isolate the logic for this step so every scraper in the project shares one tested implementation.
Sites change layouts and behavior over time -- recheck this part of the scraper on a schedule, not just at launch.
This works best over residential or ISP IPs, so the target sees ordinary browsing rather than clustered datacenter traffic.
Capture what actually failed so a broken selector or a new status code surfaces instead of getting masked by automatic retries.
A scraping framework rotates through a list of 50 real browser user agent strings, selecting one randomly for each session to avoid pattern-based detection.
Using the default user agent of your HTTP library (like python-requests/2.31.0) immediately flags your traffic as automated. Setting a realistic browser user agent is the most basic anti-detection step.
Every production scraper that routes through proxies interacts with user agent whether the developer thinks about it or not. Getting it right means fewer blocks, cleaner data, and less wasted bandwidth.
Rotate user agents per session, not per request. Real browsers keep the same user agent string for their entire browsing session, from the homepage to checkout. Changing it on every request is itself a detectable pattern, since no genuine visitor switches browsers mid-session on a single site.
Check your own browser at whatismybrowser.com, or pull a wider list from a database like useragentstring.com. Update your saved user agent list every few months, since browser and Chrome version numbers change frequently and an outdated string can look as suspicious as no string at all.
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