Skip to content


Repository files navigation

useragent - high performance user agent parser for Node.js

Useragent originated as port of's user agent parser project also known as ua-parser. Useragent allows you to parse user agent strings with high performance and accuracy by using hand tuned regular expressions for browser matching. This database is needed to ensure that every browser is correctly parsed as every browser vendor implements it's own user agent schema. This is why regular user agent parsers have major issues because they will most likely parse out the wrong browser name or confuse the render engine version with the actual version of the browser.

Build status BuildStatus

High performance

The module has been developed with a benchmark driven approach. It has a pre-compiled library that contains all the Regular Expressions and uses deferred or on demand parsing for Operating System and device information. All this engineering effort has been worth it as this benchmark shows:

Starting the benchmark, parsing 62 useragent strings per run

Executed benchmark against node module: "useragent"
Count (61), Cycles (5), Elapsed (5.559), Hz (1141.3739447904327)

Executed benchmark against node module: "useragent_parser"
Count (29), Cycles (3), Elapsed (5.448), Hz (545.6817291171243)

Executed benchmark against node module: "useragent-parser"
Count (16), Cycles (4), Elapsed (5.48), Hz (304.5373431830105)

Executed benchmark against node module: "ua-parser"
Count (54), Cycles (3), Elapsed (5.512), Hz (1018.7561434659247)

Module: "useragent" is the user agent fastest parser.

Hand tuned regular expressions

This module relies on uap-core's regexes.yaml user agent database to parse user agent strings.

This database is up-to-date thanks to contributors such as you. Feel free to submit issues and pull requests.


Installation is done using the Node Package Manager (NPM). If you don't have NPM installed on your system you can download it from

npm install useragent --save

The --save flag tells NPM to automatically add it to your package.json file.


Include the useragent parser in you node.js application:

var useragent = require('useragent');

The useragent library allows you do use the automatically installed RegExp library or you can fetch it live from the remote servers. So if you are paranoid and always want your RegExp library to be up to date to match with agent the widest range of useragent strings you can do:

var useragent = require('useragent');

This will async load the database from the server and compile it to a proper JavaScript supported format. If it fails to compile or load it from the remote location it will just fall back silently to the shipped version. If you want to use this feature you need to add yamlparser and request to your package.json

npm install yamlparser --save
npm install request --save

useragent.parse(useragent string[, js useragent]);

This is the actual user agent parser, this is where all the magic is happening. The function accepts 2 arguments, both should be a string. The first argument should the user agent string that is known on the server from the req.headers.useragent header. The other argument is optional and should be the user agent string that you see in the browser, this can be send from the browser using a xhr request or something like this. This allows you detect if the user is browsing the web using the Chrome Frame extension.

The parser returns a Agent instance, this allows you to output user agent information in different predefined formats. See the Agent section for more information.

var agent = useragent.parse(req.headers['user-agent']);

// example for parsing both the useragent header and a optional js useragent
var agent2 = useragent.parse(req.headers['user-agent'], req.query.jsuseragent);

The parse method returns a Agent instance which contains all details about the user agent. See the Agent section of the API documentation for the available methods.

useragent.lookup(useragent string[, js useragent]);

This provides the same functionality as above, but it caches the user agent string and it's parsed result in memory to provide faster lookups in the future. This can be handy if you expect to parse a lot of user agent strings.

It uses the same arguments as the useragent.parse method and returns exactly the same result, but it's just cached.

var agent = useragent.lookup(req.headers['user-agent']);

And this is a serious performance improvement as shown in this benchmark:

Executed benchmark against method: "useragent.parse"
Count (49), Cycles (3), Elapsed (5.534), Hz (947.6844321931629)

Executed benchmark against method: "useragent.lookup"
Count (11758), Cycles (3), Elapsed (5.395), Hz (229352.03831239208)


Transforms the JSON representation of a Agent instance back in to a working Agent instance

var agent = useragent.parse(req.headers['user-agent'])
  , another = useragent.fromJSON(JSON.stringify(agent));

console.log(agent == another); string).browsername;

This api provides you with a quick and dirty browser lookup. The underlying code is usually found on client side scripts so it's not the same quality as our useragent.parse method but it might be needed for legacy reasons. returns a object with potential matched browser names['user-agent']).firefox // true['user-agent']).safari // false
var ua =['user-agent'])

// the object
  version: '3'
  webkit: false
  opera: false
  ie: false
  chrome: false
  safari: false
  mobile_safari: false
  firefox: true
  mozilla: true
  android: false

Agents, OperatingSystem and Device instances

Most of the methods mentioned above return a Agent instance. The Agent exposes the parsed out information from the user agent strings. This allows us to extend the agent with more methods that do not necessarily need to be in the core agent instance, allowing us to expose a plugin interface for third party developers and at the same time create a uniform interface for all versioning.

The Agent has the following property

  • family The browser family, or browser name, it defaults to Other.
  • major The major version number of the family, it defaults to 0.
  • minor The minor version number of the family, it defaults to 0.
  • patch The patch version number of the family, it defaults to 0.

In addition to the properties mentioned above, it also has 2 special properties, which are:

  • os OperatingSystem instance
  • device Device instance

When you access those 2 properties the agent will do on demand parsing of the Operating System or/and Device information.

The OperatingSystem has the same properties as the Agent, for the Device we don't have any versioning information available, so only the family property is set there. If we cannot find the family, they will default to Other.

The following methods are available:


Returns the family and version number concatinated in a nice human readable string.

var agent = useragent.parse(req.headers['user-agent']);
agent.toAgent(); // 'Chrome 15.0.874'


Returns the results of the Agent.toAgent() but also adds the parsed operating system to the string in a human readable format.

var agent = useragent.parse(req.headers['user-agent']);
agent.toString(); // 'Chrome 15.0.874 / Mac OS X 10.8.1'

// as it's a to string method you can also concat it with another string
'your useragent is ' + agent;
// 'your useragent is Chrome 15.0.874 / Mac OS X 10.8.1'


Returns the version of the browser in a human readable string.

var agent = useragent.parse(req.headers['user-agent']);
agent.toVersion(); // '15.0.874'


Generates a JSON representation of the Agent. By using the toJSON method we automatically allow it to be stringified when supplying as to the JSON.stringify method.

var agent = useragent.parse(req.headers['user-agent']);
agent.toJSON(); // returns an object



Generates a stringified version of operating system;

var agent = useragent.parse(req.headers['user-agent']);
agent.os.toString(); // 'Mac OSX 10.8.1'


Generates a stringified version of operating system's version;

var agent = useragent.parse(req.headers['user-agent']);
agent.os.toVersion(); // '10.8.1'


Generates a JSON representation of the OperatingSystem. By using the toJSON method we automatically allow it to be stringified when supplying as to the JSON.stringify method.

var agent = useragent.parse(req.headers['user-agent']);
agent.os.toJSON(); // returns an object



Generates a stringified version of device;

var agent = useragent.parse(req.headers['user-agent']);
agent.device.toString(); // 'Asus A100'


Generates a stringified version of device's version;

var agent = useragent.parse(req.headers['user-agent']);
agent.device.toVersion(); // '' , no version found but could also be '0.0.0'


Generates a JSON representation of the Device. By using the toJSON method we automatically allow it to be stringified when supplying as to the JSON.stringify method.

var agent = useragent.parse(req.headers['user-agent']);
agent.device.toJSON(); // returns an object


Adding more features to the useragent

As I wanted to keep the core of the user agent parser as clean and fast as possible I decided to move some of the initially planned features to a new plugin file.

These extensions to the Agent prototype can be loaded by requiring the useragent/features file:

var useragent = require('useragent');

The initial release introduces 1 new method, satisfies, which allows you to see if the version number of the browser satisfies a certain range. It uses the semver library to do all the range calculations but here is a small summary of the supported range styles:

  • >1.2.3 Greater than a specific version.
  • <1.2.3 Less than.
  • 1.2.3 - 2.3.4 := >=1.2.3 <=2.3.4.
  • ~1.2.3 := >=1.2.3 <1.3.0.
  • ~1.2 := >=1.2.0 <2.0.0.
  • ~1 := >=1.0.0 <2.0.0.
  • 1.2.x := >=1.2.0 <1.3.0.
  • 1.x := >=1.0.0 <2.0.0.

As it requires the semver module to function you need to install it seperately:

npm install semver --save

Agent.satisfies('range style here');

Check if the agent matches the supplied range.

var agent = useragent.parse(req.headers['user-agent']);
agent.satisfies('15.x || >=19.5.0 || 25.0.0 - 17.2.3'); // true
agent.satisfies('>16.12.0'); // false


For small changes between version please review the changelog.

Upgrading from 1.10 to 2.0.0

  • useragent.fromAgent has been removed.
  • agent.toJSON now returns an Object, use JSON.stringify(agent) for the old behaviour.
  • agent.os is now an OperatingSystem instance with version numbers. If you still a string only representation do agent.os.toString().
  • semver has been removed from the dependencies, so if you are using the require('useragent/features') you need to add it to your own dependencies

Upgrading from 0.1.2 to 1.0.0

  • useragent.browser(ua) has been renamed to
  • useragent.parser(ua, jsua) has been renamed to useragent.parse(ua, jsua).
  • result.pretty() has been renamed to result.toAgent().
  • result.V1 has been renamed to result.major.
  • result.V2 has been renamed to result.minor.
  • result.V3 has been renamed to result.patch.
  • result.prettyOS() has been removed.
  • result.match has been removed.