Detecting user agents in php

Every time you use your browser to access a website a User-Agent header is sent to the respective server.
Detecting user agents on the server can be useful for many reasons.

1. Browsers Quirks – Despite the standardization in browsers, there will remain some quirks in various browsers that you will need to iron out on a regular basis.
2. Personalize Content – It may be required to deliver different type of content depending on the browser type (although it is usually not recommended); whether mobile or otherwise.
3. Illegal Access – Prevent bandwidth hogging bots and poorly programmed clients from downloading your content.

Below is a sample header for my site when using Firefox.

GET / HTTP/1.1
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:
Gecko/2009011913 Firefox/3.0.6 FirePHP/0.2.4
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive

PHP already has a builtin function – get_browser() that lets you determine the capabilities of the user’s browser, but it requires a browscap.ini to be installed, which sadly is not bundled with PHP, and also the function can slow down your php script. The other way to get a user agent is to use php server variables like below,


In this post we will use the Net_UserAgent_Detect Pear package to determine user agents.


Net_UserAgent_Detect being a Pear package we will use the Pear installer as below. I recommend to always use the Pear installer to download packages rather than downloading it manually as the Pear installer automatically downloads any dependent packages.

pear install Net_UserAgent_Detect-2.5.1


Usage is quite simple. For example the following code:

will return the following string on Firefox 3.0.6: This can be quite useful if you need to log the users browser or OS type.

Mozilla/5.0 (Windows; U; Windows NT 5.1; 
en-US; rv: Gecko/2009011913 Firefox/3.0.6 FirePHP/0.2.4

getUserAgent() is only one of the many methods available in the class.

echo('OS String: '.Net_UserAgent_Detect::getOSString())."
"; echo('Javascript: '.Net_UserAgent_Detect::getFeature('javascript')); ?>

Some other useful functions to directly test the type of browser are:
isNavigator( )
isNetscape( )

So to detect if the user is running Firefox:

$browser = Net_UserAgent_Detect::isNetscape();

3 thoughts to “Detecting user agents in php”

  1. i just went through this in a recent project. I didn’t go with the PEAR package, but instead landed on a class called browscap, which basically goes out and fetches the browscap.ini file via cURL and stores it locally in cache. It even parses the ini file into an array and caches that result for even quicker response.

    You can set the script to autofetch new versions if you want as well.

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