Basic usage#


If you have not yet installed Composer, refer to the Intro chapter.

composer.json: Project Setup#

To start using Composer in your project, all you need is a composer.json file. This file describes the dependencies of your project and may contain other metadata as well.

The JSON format is quite easy to write. It allows you to define nested structures.

The require Key#

The first (and often only) thing you specify in composer.json is the require key. You're simply telling Composer which packages your project depends on.

    "require": {
        "monolog/monolog": "1.0.*"

As you can see, require takes an object that maps package names (e.g. monolog/monolog) to package versions (e.g. 1.0.*).

Package Names#

The package name consists of a vendor name and the project's name. Often these will be identical - the vendor name just exists to prevent naming clashes. It allows two different people to create a library named json, which would then just be named igorw/json and seldaek/json.

Here we are requiring monolog/monolog, so the vendor name is the same as the project's name. For projects with a unique name this is recommended. It also allows adding more related projects under the same namespace later on. If you are maintaining a library, this would make it really easy to split it up into smaller decoupled parts.

Package Versions#

In the previous example we were requiring version 1.0.* of monolog. This means any version in the 1.0 development branch. It would match 1.0.0, 1.0.2 or 1.0.20.

Version constraints can be specified in a few different ways.

Name Example Description
Exact version 1.0.2 You can specify the exact version of a package.
Range >=1.0 >=1.0 <2.0 >=1.0 <1.1 || >=1.2 By using comparison operators you can specify ranges of valid versions. Valid operators are >, >=, <, <=, !=.
You can define multiple ranges. Ranges separated by a space ( ) or comma (,) will be treated as a logical AND. A double pipe (||) will be treated as a logical OR. AND has higher precedence than OR.
Hyphen Range 1.0 - 2.0 Inclusive set of versions. Partial versions on the right include are completed with a wildcard. For example 1.0 - 2.0 is equivalent to >=1.0.0 <2.1 as the 2.0 becomes 2.0.*. On the other hand 1.0.0 - 2.1.0 is equivalent to >=1.0.0 <=2.1.0.
Wildcard 1.0.* You can specify a pattern with a * wildcard. 1.0.* is the equivalent of >=1.0 <1.1.
Tilde Operator ~1.2 Very useful for projects that follow semantic versioning. ~1.2 is equivalent to >=1.2 <2.0. For more details, read the next section below.
Caret Operator ^1.2.3 Very useful for projects that follow semantic versioning. ^1.2.3 is equivalent to >=1.2.3 <2.0. For more details, read the next section below.

Next Significant Release (Tilde and Caret Operators)#

The ~ operator is best explained by example: ~1.2 is equivalent to >=1.2 <2.0.0, while ~1.2.3 is equivalent to >=1.2.3 <1.3.0. As you can see it is mostly useful for projects respecting semantic versioning. A common usage would be to mark the minimum minor version you depend on, like ~1.2 (which allows anything up to, but not including, 2.0). Since in theory there should be no backwards compatibility breaks until 2.0, that works well. Another way of looking at it is that using ~ specifies a minimum version, but allows the last digit specified to go up.

The ^ operator behaves very similarly but it sticks closer to semantic versioning, and will always allow non-breaking updates. For example ^1.2.3 is equivalent to >=1.2.3 <2.0.0 as none of the releases until 2.0 should break backwards compatibility. For pre-1.0 versions it also acts with safety in mind and treats ^0.3 as >=0.3.0 <0.4.0

Note: Though 2.0-beta.1 is strictly before 2.0, a version constraint like ~1.2 would not install it. As said above ~1.2 only means the .2 can change but the 1. part is fixed.

Note: The ~ operator has an exception on its behavior for the major release number. This means for example that ~1 is the same as ~1.0 as it will not allow the major number to increase trying to keep backwards compatibility.


By default only stable releases are taken into consideration. If you would like to also get RC, beta, alpha or dev versions of your dependencies you can do so using stability flags. To change that for all packages instead of doing per dependency you can also use the minimum-stability setting.

If you are using range comparisons when selecting non-stable packages, and you specify a numeric version number (that is, no suffix indicating alpha, beta, rc, or stable), then both non-stable and stable versions of a particular release number will be treated as equally valid.

If you wish to consider only the stable release in the comparison, add the suffix -stable to the version number.

Here are some examples:

Example Interpretation
>=1.0.0 Any release, stable or non-, of 1.0.0 will be allowed
>=1.0.0-stable Only the stable release of 1.0.0 will be allowed
<2.0.0 Neither release, stable or non-, of 2.0.0 will be allowed
<2.0.0-stable Only the stable release of 2.0.0 will be disallowed; non-stable releases will be allowed

Note that the packages matched by these constraints are still checked against the minimum-stability setting and each package's stability flags.

Test version constraints#

You can test version constraints using Fill in a package name and it will autofill the default version constraint which Composer would add to your composer.json file. You can adjust the version constraint and the tool will highlight all releases that match.

Installing Dependencies#

To fetch the defined dependencies into your local project, just run the install command of composer.phar.

php composer.phar install

This will find the latest version of monolog/monolog that matches the supplied version constraint and download it into the vendor directory. It's a convention to put third party code into a directory named vendor. In case of monolog it will put it into vendor/monolog/monolog.

Tip: If you are using git for your project, you probably want to add vendor into your .gitignore. You really don't want to add all of that code to your repository.

Another thing that the install command does is it adds a composer.lock file into your project root.

composer.lock - The Lock File#

After installing the dependencies, Composer writes the list of the exact versions it installed into a composer.lock file. This locks the project to those specific versions.

Commit your application's composer.lock (along with composer.json) into version control.

This is important because the install command checks if a lock file is present, and if it is, it downloads the versions specified there (regardless of what composer.json says).

This means that anyone who sets up the project will download the exact same version of the dependencies. Your CI server, production machines, other developers in your team, everything and everyone runs on the same dependencies, which mitigates the potential for bugs affecting only some parts of the deployments. Even if you develop alone, in six months when reinstalling the project you can feel confident the dependencies installed are still working even if your dependencies released many new versions since then.

If no composer.lock file exists, Composer will read the dependencies and versions from composer.json and create the lock file after executing the update or the install command.

This means that if any of the dependencies get a new version, you won't get the updates automatically. To update to the new version, use the update command. This will fetch the latest matching versions (according to your composer.json file) and also update the lock file with the new version.

php composer.phar update

Note: Composer will display a Warning when executing an install command if composer.lock and composer.json are not synchronized.

If you only want to install or update one dependency, you can whitelist them:

php composer.phar update monolog/monolog [...]

Note: For libraries it is not necessarily recommended to commit the lock file, see also: Libraries - Lock file.


Packagist is the main Composer repository. A Composer repository is basically a package source: a place where you can get packages from. Packagist aims to be the central repository that everybody uses. This means that you can automatically require any package that is available there.

If you go to the packagist website (, you can browse and search for packages.

Any open source project using Composer should publish their packages on packagist. A library doesn't need to be on packagist to be used by Composer, but it makes life quite a bit simpler.


For libraries that specify autoload information, Composer generates a vendor/autoload.php file. You can simply include this file and you will get autoloading for free.

require 'vendor/autoload.php';

This makes it really easy to use third party code. For example: If your project depends on monolog, you can just start using classes from it, and they will be autoloaded.

$log = new Monolog\Logger('name');
$log->pushHandler(new Monolog\Handler\StreamHandler('app.log', Monolog\Logger::WARNING));


You can even add your own code to the autoloader by adding an autoload field to composer.json.

    "autoload": {
        "psr-4": {"Acme\\": "src/"}

Composer will register a PSR-4 autoloader for the Acme namespace.

You define a mapping from namespaces to directories. The src directory would be in your project root, on the same level as vendor directory is. An example filename would be src/Foo.php containing an Acme\Foo class.

After adding the autoload field, you have to re-run dump-autoload to re-generate the vendor/autoload.php file.

Including that file will also return the autoloader instance, so you can store the return value of the include call in a variable and add more namespaces. This can be useful for autoloading classes in a test suite, for example.

$loader = require 'vendor/autoload.php';
$loader->add('Acme\\Test\\', __DIR__);

In addition to PSR-4 autoloading, classmap is also supported. This allows classes to be autoloaded even if they do not conform to PSR-4. See the autoload reference for more details.

Note: Composer provides its own autoloader. If you don't want to use that one, you can just include vendor/composer/autoload_*.php files, which return associative arrays allowing you to configure your own autoloader.

Intro | Libraries

Found a typo? Something is wrong in this documentation? Just fork and edit it!