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What Is a User Agent?#

Browsers identify themselves to websites with a User-Agent string in the request header. The user agent string contains information about:

  • Browser type
  • Browser version
  • Operating system and platform

Websites use this information to provide the best possible user experience, or sometimes to block certain features or identify automated bots so that they can be excluded from analytics.

User agents come in many forms and can look like this:

Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:124.0) Gecko/20100101 Firefox/124.0

Learn more about user agents and what they can do.

How to Set User Agent#

Note

Few browsers allow you to set the User-Agent on the fly, but most allow you to set it at the start of a session. See the table of supported browsers below for details.

For a Session#

How to set the user agent in the beginning of a session:

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from browserist import Browser, BrowserSettings

settings = BrowserSettings(user_agent="MyUserAgent")

with Browser(settings) as browser:
    browser.open.url("https://example.com")
    user_agent = browser.user_agent.get()
    print(user_agent)

How it appears in the terminal:

MyUserAgent

On the Fly#

Basic Usage:#

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from browserist import Browser

with Browser() as browser:
    browser.user_agent.set("MyUserAgent")
    browser.open.url("https://example.com")
    user_agent = browser.user_agent.get()
    print(user_agent)

How it appears in the terminal:

MyUserAgent

Append to Existing User Agent:#

If you want to identify your sessions, for instance to exclude bot traffic from your analytics, you can append the existing user agent with a custom value. Imagine that a browser's default user agent is:

Mozilla/5.0

Let's add a custom value to it:

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from browserist import Browser

with Browser() as browser:
    user_agent = browser.user_agent.get()
    user_agent += " MyUserAgent"
    browser.user_agent.set(user_agent)
    browser.open.url("https://example.com")
    new_user_agent = browser.user_agent.get()
    print(new_user_agent)

How the user agent now appears in the terminal:

Mozilla/5.0 MyUserAgent

Supported Browsers#

Most browsers support setting the User-Agent at the start of a session, but only a few allow you to set it on the fly:

Case Chrome Edge Firefox Safari Internet Explorer
For a session
On the fly

How to Randomize User Agent#

As example for advanced usage, you can randomize the user agent per session or on the fly.

Per Session#

Example:

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import random
from browserist import Browser, BrowserSettings

USER_AGENTS = [
    "MyUserAgent1",
    "MyUserAgent2",
    "MyUserAgent3",
]

user_agent = random.choice(USER_AGENTS)
settings = BrowserSettings(user_agent=user_agent)

with Browser(settings) as browser:
    browser.open.url("https://example.com")

On the Fly#

Example:

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import random
from browserist import Browser

USER_AGENTS = [
    "MyUserAgent1",
    "MyUserAgent2",
    "MyUserAgent3",
]

with Browser() as browser:
    user_agent = random.choice(USER_AGENTS)
    browser.user_agent.set(user_agent)
    browser.open.url("https://example.com")