Customizing HTTPX User Agents for Effective API Requests

Feb 5, 2024 ยท 2 min read

When making requests to web APIs, the User-Agent header allows the API server to identify the application or client making the request. Setting a custom user agent can be beneficial for analytics, compatibility checks, or access control on the server side. The HTTPX Python library makes it easy to configure user agents for your API clients.

Why Customize the User Agent

The default HTTPX user agent looks something like "python-httpx/0.23.0". While this identifies the client as a HTTPX program, it doesn't provide much additional context.

Some reasons you may want to customize the user agent string:

  • Analytics: The API provider may track usage statistics based on the user agent. A custom user agent allows them to identify and attribute requests coming from your application.
  • Compatibility Checks: The server can identify client types and versions to check for compatibility with the API or selectively enable/disable features.
  • Access Control: User agents can be allowlisted to control access or rate limiting based on the client application.
  • Setting a Custom User Agent with HTTPX

    To set a custom user-agent, specify the http2_client parameter when creating the HTTPX client:

    import httpx
    user_agent = "my_app_name/1.0.0"
    client = httpx.Client(http2_client=httpx.Client(headers={"user-agent": user_agent}))

    Now any requests made with this client will send the custom user agent string.

    Some tips when creating a user agent string:

  • Include the application name and version
  • Keep it simple and descriptive
  • Avoid anything misleading or suggesting the request is from a browser or human
  • User Agent Format Standards

    There are some common standards and formats used by browsers and crawlers when constructing user agent strings. Using these standards can help ensure compatibility with servers that parse the user agent header.

    Some examples:

  • Mozilla format: AppName/Version (SystemInfo) Library/LibraryVersion
  • Googlebot format: Googlebot/Version (+
  • Setting a thoughtful custom user agent on your HTTPX client can provide more visibility for API analytics and compatibility with certain server use cases. Just be sure not to misrepresent your application!

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