List of user agent strings

ByPaul Christiano Last Update on

If you‘re involved in web scraping, you‘ve likely come across the term "user agent" before. But what exactly are user agents, and why are they so crucial for successful web scraping? In this in-depth guide, we‘ll cover everything you need to know about user agents and how to leverage them to collect the web data you need while avoiding dreaded IP bans and CAPTCHAs.

What is a User Agent?

In simple terms, a user agent (UA) is a line of text that identifies the client software accessing a website. The UA string contains details about your web browser, operating system, device type, and more.

Every time you visit a webpage, your browser sends a user agent as part of the HTTP request header. This allows the web server to tailor the response based on your system and browser, optimizing compatibility and user experience.

A typical user agent string looks something like this:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36

This particular UA conveys the following:

  • Mozilla/5.0 – Historical artifact from the Netscape days
  • Windows NT 10.0 – The user‘s operating system (Windows 10)
  • Win64; x64 – 64-bit processor architecture
  • AppleWebKit/537.36 – The browser engine (from Apple/Safari)
  • Chrome/96.0.4664.110 – The actual browser (Google Chrome version 96)
  • Safari/537.36 – Another historical artifact related to Safari

As you can see, the UA string packs a lot of detail into a compact format. By parsing the UA, websites can serve content, layout, ads, etc. that are tailored to your setup.

Why User Agents Matter for Web Scraping

So why do user agents matter so much when it comes to web scraping? There are a few key reasons:

1. Avoiding Bans and Blocks

Many websites are not fond of bots and web scrapers, as they can drain server resources and "steal" valuable data. As a result, sites often try to detect and block requests that appear to come from scrapers.

One of the easiest ways websites identify bots is by examining the user agent. If you send a generic UA like "Python Requests Library" or an empty UA string, the site will almost certainly flag you as a bot and block your IP address.

To avoid this, you need to mimic a real web browser by using an authentic user agent string in your scraper. Something like the Chrome UA shown earlier is a good bet, as it looks just like a human visitor.

2. Accessing the Correct Website Version

Some websites serve different versions based on the user agent. For example, you may get a stripped-down mobile layout if you visit from an iPhone UA string.

If you‘re trying to scrape a website that behaves this way, using the appropriate UA is critical to getting the full desktop version of the page. Choosing the wrong UA could mean missing out on valuable data points only present on certain page variants.

3. Bypassing Anti-Bot Systems

More sophisticated anti-bot systems go beyond just checking the user agent. They look for other signs of "non-human" behavior like abnormally fast requests, missing cookies, javascript discrepancies, and more.

However, even these advanced setups still rely heavily on UA strings as a first line of defense. By using a legitimate, widely-used browser user agent, you greatly increase your odds of slipping past basic bot detection filters. It‘s not a complete solution, but a valid UA lays the necessary groundwork.

Tips for Using User Agents When Web Scraping

Now that we understand the importance of user agents for web scraping, let‘s look at some actionable tips you can apply in your own projects:

1. Use Real Browser User Agents

As mentioned, you should always aim to use authentic user agent strings that match popular web browsers. Don‘t try to make up your own or use ones associated with web scrapers/spiders.

Here are a few examples of UA strings used by major browsers:

Chrome:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36

Firefox:
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0

Safari:
Mozilla/5.0 (Macintosh; Intel Mac OS X 12_0_1) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.0 Safari/605.1.15

Edge:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36 Edg/96.0.1054.62

You can find extensive lists of user agent strings online to choose from. Focus on popular, modern browsers for the best results.

2. Rotate Your User Agents

Using a single user agent is often not enough, especially if you‘re scraping a large site. You need to switch up your UAs periodically to avoid establishing a pattern.

Think about it – if a website suddenly gets thousands of requests from the exact same Chrome UA, that‘s going to look mighty suspicious. But if those requests come from a mix of Chrome, Firefox, Safari, and Edge UAs, it seems much more organic.

Set up your scraper to randomly choose from a pool of UA strings for each new request. Make sure to use UAs for a variety of browsers and operating systems (Windows, Mac, Linux, Android, iOS) for diversity.

3. Use Proxies in Tandem with User Agents

Rotating user agents is a good start, but it‘s often not sufficient on its own. Websites can still see that all the varying UAs are coming from the same IP address, which is a big red flag.

To really fly under the radar, you need to distribute your requests across multiple IP addresses using proxies. Proxies act as intermediaries, sending your requests from different IP addresses to obscure the true source.

When you combine user agent rotation with proxy rotation, you create a very convincing mix of requests that look to come from many different users in different locations. This greatly reduces your chance of being detected and blocked.

Look for proxies that allow easy IP rotation and support custom user agent headers for best results. Many proxy providers even offer UA rotation as a built-in feature for web scraping clients.

Implementing User Agent Rotation

Let‘s look at a quick example of how you can implement basic user agent rotation in Python using the requests library:


import requests
import random

user_agents = [
"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36",
"Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0",
"Mozilla/5.0 (Macintosh; Intel Mac OS X 12_0_1) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.0 Safari/605.1.15",
"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36 Edg/96.0.1054.62"
]

url = "https://example.com"

ua = random.choice(user_agents)
headers = {"User-Agent": ua}
response = requests.get(url, headers=headers)

print(f"User Agent: {ua}")
print(f"Response: {response.status_code}")

This script defines a list of UA strings and randomly selects one for each request. The chosen UA is passed in the headers argument of requests.get().

For more advanced projects, consider using a dedicated web scraping tool like ScraperAPI, ScrapingBee, or others that manage user agents, proxies, CAPTCHAs, and more out of the box.

Checking Your User Agent

To test if your UA rotation is working, you can print the UA string as shown in the example above and visually check that it‘s changing.

For a live test, you can visit websites like WhatIsMyBrowser.com or WhatIsMyUserAgent.com which echo back your current UA. Scrape these sites with your script and see if the correct UAs are reflected.

Browser developer tools are also useful for inspecting your UA. In Chrome, open the Developer Tools (F12), go to the Network tab, and examine the request headers. You should see your chosen UA string under User-Agent.

Conclusion

User agents are a fundamental component of web scraping that can make or break your projects. Using authentic, rotating UAs is essential for avoiding IP bans and ensuring you get the right web page version.

Pair your user agentStrategy with proxy rotation for the most robust scraping setup. Choose UA strings from popular web browsers and steer clear of ones associated with bots or scrapers.

With the knowledge and tactics covered in this guide, you‘re well-equipped to scrape effectively using user agents. Remember to always respect website terms of service and robots.txt instructions. Happy scraping!

I am Paul Christiano, a fervent explorer at the intersection of artificial intelligence, machine learning, and their broader implications for society. Renowned as a leading figure in AI safety research, my passion lies in ensuring that the exponential powers of AI are harnessed for the greater good. Throughout my career, I've grappled with the challenges of aligning machine learning systems with human ethics and values. My work is driven by a belief that as AI becomes an even more integral part of our world, it's imperative to build systems that are transparent, trustworthy, and beneficial. I'm honored to be a part of the global effort to guide AI towards a future that prioritizes safety and the betterment of humanity.

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