PHP Dependency Management Using Composer

PHP dependency management is a critical component of modern PHP development. In fact, according to the 2025 PHP Landscape Report, managing dependencies was the third largest challenge for developers using PHP in their critical applications, from small web apps up to enterprise systems. Many, if not most, of these teams likely turn to using Composer as a solution.

In this blog, I give an overview of PHP dependency management, including what it is, common challenges, and how Composer became the go-to answer. I then introduce Composer, covering the basics, commands to know, and best practices your developer team can use now to improve your dependency management.

What Is Dependency Management in PHP?

PHP dependency management is the process of handling external libraries and packages within a PHP project.

Instead of writing every feature from scratch, developers often turn to third-party code to accomplish various goals, such as PHP logging, authentication, or database access. Dependency management tools ensure the packages providing this code are installed, kept at compatible versions, and updated when needed.

Common PHP Dependency Management Challenges

Before dependency management tooling existed for PHP, and even to an extent still today, the process has been:

• Grab a package containing the required third-party code at the version you need.
• Install it somewhere in your source tree.
• Either use PHP’s `include` and `require` statements to pull code in where you need it, or use a PHP autoloader to automate loading class definitions.

There are many places this can go wrong:

• You could grab the wrong package version.
• The version of the package you install may have a security issue reported against it, requiring you to re-install from a new version.
• The package might require additional third-party libraries. If these are not bundled with the package, you will then need to track down and install these as well.
• The package may use different versions of a third-party library than the version you already have installed, or worse, the two versions might not even be compatible, preventing you from using one or more libraries.
• You end up having to check in the third-party dependencies within your source code repository in order to ensure the correct versions are always installed, leading to longer checkout times and increased storage within your source control.

Additionally, keeping all dependencies current can often be difficult. Teams may delay updates to avoid breaking changes, ultimately resulting in outdated code, increased security risks, and compatibility issues with newer PHP or framework versions that must be addressed. Add in abandoned or unmaintained packages, and PHP dependency management suddenly becomes an impossibly large task.

The Development of a PHP Dependency Manager

With this situation in place, the PHP ecosystem identified dependency management as an issue to tackle from its earliest years. In general, dependency management provides a standardized tool for identifying, downloading, and installing packages. Ideally, it will also manage version compatibility, and validate that dependencies are installed so they will not conflict with the version requirements of the application author.

From very early days, PHP bundled the PEAR installer. PEAR stands for PHP Extension and Application Repository and was modeled loosely on Perl’s CPAN (Comprehensive Perl Archive Network). OSS developers could submit packages to be included in PEAR, and, once they were, the installer provided a way for you to install the packages globally on your system. 

You would setup PHP’s include_path INI setting to make it easier to include or require the code in your application. PEAR is also the tooling behind PECL, which has been used for years to manage, build, and install PHP extensions.

This approach worked to an extent, but suffered a few problems:

• If you had multiple applications on your server, you were forced to have all of them depend on the exact same versions of each PEAR package you installed; there was no way to install multiple versions side by side. This also meant that if one PEAR library depended on another, you were forced to choose versions that were compatible with each other.
• The process for inclusion in PEAR was rather difficult, and suffered heavily from gatekeeping. You could package your code to be installed by PEAR, but the installer would not be able to fetch it unless it was on the central PEAR archive.
• It predated autoloading, forcing you to use include/require long after autoloading was a thing.

Sometime during the late PHP 4 era, a rewrite gave the ability to add channels, and for people to deploy their own PEAR archive servers. This solved the second point above, as companies and OSS projects and authors could deploy their own PEAR servers, and users could then add these as PEAR channels to install from.

In 2011, Nils Adermann and Jordi Boggiano decided that the PEAR installer was too limiting, and started work on what would become Composer. Using Composer has since become the de facto standard for PHP dependency management; most frameworks and PHP applications install via or with Composer.

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What Is Composer?

Composer is the standard tool for PHP dependency management.

It is designed to simplify how projects bring in and manage external libraries. Rather than manually downloading code, unpacking it, and ensuring all the right versions are installed, Composer automates this process and keeps everything consistent across environments.

Understanding the fundamentals of Composer gives you increased control over your project. After all, using Composer for PHP dependency management removes the guesswork, allowing you to work more efficiently, avoid configuration drift, and ensure your PHP applications remain stable.

What Does Composer Do?

At its core, Composer manages three key tasks: resolving and installing dependencies, autoloading, and security scanning.

Resolving and Installing Dependencies 

Composer fetches the libraries your project requires and places them in a vendor/ directory. If a library has additional dependencies, Composer also fetches and installs those, ensuring that if any given dependency is required by multiple libraries, versions retain compatibility. The tooling will inform you of dependency conflicts, allowing you to resolve them in order to get a viable installation.

The primary location it searches for dependencies is packagist.org, where any library author can register their library for installation. However, you can create your own Composer repositories from which to pull dependencies, point to third-party repositories, and even point to source code repositories from which to pull code directly.

Autoloading

Composer generates an autoloader file so your application can instantly use the installed packages without extra configuration. While class-based autoloading is baked into PHP, Composer has support for a number of different autoloading strategies, as well as a way for packages to specify files to always load – which enables function and constant autoloading as well.

Security Scanning

Composer consults a number of security lists to identify software versions affected by vulnerabilities. When installing a version that has vulnerabilities reported against it, it will report this information; you can also invoke it in a way such that it fails if any libraries have security issues for the resolved versions.

This means developers don’t need to worry about hunting down every underlying requirement, or tracking security lists for each. If you need a logging library, for example, Composer not only installs it but also installs anything that library depends on, and notifies you if doing so would install an insecure version.

Learn More About Common PHP Vulnerabilities

Installing Composer

Composer's Getting Started guide covers system requirements and installation. The project offers both some programmatic ways to fetch and install it, as well as stable downloads. Composer itself is shipped as a PHAR file, and runs using the PHP interpreter itself.

Core Composer Commands to Know for PHP Dependency Management

While Composer offers a wide range of features, most developers only need a handful of commands for day-to-day work. These commands cover installing dependencies, adding new packages, and keeping everything up to date. Understanding them will give you a solid foundation for managing dependencies efficiently in any PHP project.

composer require

This is the meat and potatoes of using Composer. With this command, you can specify a package your application or project will require, optionally with a version constraint. If it's able to resolve the package and version:

• It will add an entry to the "require" section of your composer.json, where the key is the package name and the value is the version constraint. If you didn't supply a version constraint, it will use one that allows updating within the same semantic version of the latest version available.
• It will download it and install it within the vendor/ subdirectory
• It will write an entry to another file, composer.lock, with information on the version installed, and a hash of the package archive. This ensures that if you install again, you install the exact same version.

But what exactly is a version constraint? It can be a number of things, as displayed in the table below.

On top of these, you can also specify stability constraints (e.g. stable, dev, beta, alpha, etc.). The Composer project highly recommends being conservative and precise with your constraints to ensure ease of updating and to prevent version conflicts.

composer update

Let's say it's been a month or two since you last made a change to your project. Chances are that many, if not all, of your dependencies have new releases that either fix bugs or patch security issues. How do you update your project?

The update subcommand is your friend here.

You can run composer update without arguments, or with one or more package names. It will then determine if any newer versions exist that fit within your constraints, and determine if the new version conflicts with the constraints of any other packages it maintains in your installation. If successful, it will update the packages, including updating the composer.lock file with the installation details, as well as update the Composer autoloader to ensure that the package assets can be accessed.

composer install

One of the benefits of using Composer is that you can stop storing your package dependencies themselves as part of your project. Instead, you will commit your composer.json and composer.lock files, and exclude your vendor/ subdirectory from version control.

However, what happens if you perform a fresh checkout of your project? Or a team member checks out the project, or updates from the latest changes in the repository? The dependencies aren't part of the checkout, so how do they test and run the application?

They install the dependencies.

The composer.lock file contains the list of specific versions installed and hashes to verify them when Composer fetches them. The composer install command will install the dependencies based on the lockfile, ensuring that they are exactly as the last person who updated intended.

Even better: this command allows you to choose whether or not development requirements should be installed (more on that later), whether or not to create an optimized autoloader (which provides performance benefits in production), whether or not to allow fetching source packages versus distribution packages, and more. As such, this also becomes your tool for installing production-optimized dependencies for purposes of deployment!

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Options for Getting Started Using Composer

In order to list and track dependencies, you first need a composer.json file. You can get started in one of three ways: using an interactive command, creating a minimal file, or simply running any Composer commands that would update the file.

Option 1: Interactive Initialization

To get started, you will run composer init in your project's directory. This will start an interactive questionnaire, asking the project's name, type, authors, license, and more. Follow the prompts, and you'll end up with a composer.json file that you can immediately start using.

Option 2: Manual Creation

The composer.json file is just a JSON file, and at the minimum only requires the contents {}. Generally, you will include a name key detailing the project name, and a require key, which is an object of dependency packages and their versions. If you start with just {}, you are ready to go.

Option 3: Just Use Composer

The final option is to call a command such as composer require {packageName} in your directory. If no composer.json is found, it will create one, and update it to add the structure that the command would normally write to.

Best Practices for PHP Dependency Management Using Composer

While Composer makes working with libraries easier,  how you use it determines whether your project stays stable or turns into a PHP maintenance headache. Following best practices helps you avoid conflicts, reduce security risks, and keep your application sustainable over time.

composer help Is Your Best Friend

Use the help tool! composer help is a built-in command that provides documentation for Composer. It shows available commands, their descriptions, and detailed usage instructions for each. You can use composer help <command> or composer <command> --help to explore specific options and arguments. 

Composer supplies rich help support for you, documenting options and arguments in a straightforward way, so make sure to take advantage of everything it has to offer.

Separate Development and Production Dependencies

There are things you need in development that you likely don't need in production: PHP testing tools, static analysis tools, IDE stubs, and more. You can install these separate from production dependencies by passing the --dev flag to composer require:

composer require --dev phpunit/phpunit

These dependencies are stored in a separate key within your composer.json, require-dev. When you run composer install, these will be installed alongside your production packages.

When preparing to package your application for production deployment, run composer install with the option --no-dev, which will omit them.

Create Constraints for PHP and Extensions You Require

A little known trick is that you can specify the PHP versions your project will work with, as well as required extensions. This can ensure that you do not attempt to deploy to an environment that uses different versions or omits those extensions. That said, it only validates these when running an update or install operation, which means that if you are packaging for deployment separate from where you deploy, it won't help much.

You can use require to add these validations. When you do, I suggest using the --no-install and --ignore-platform-reqs flags to ensure that if you do not have these present locally, you will not have issues:

• composer update --no-install --ignore-platform-req=php php:~8.3.0\
• composer update --no-install --ignore-platform-reqs 'ext-pdo:*'

Better yet, you can make things easier for yourself by setting the "platform PHP" version. When this is defined, Composer will act as if that is the version locally that is performing an update or install operation, and only grab versions that will work with it:

• composer config platform.php 8.3.4

Audit Your Dependencies

The composer audit command will check for known CVEs posted against any of your dependencies, including PHP and extensions. This is a useful tool to run in CI/CD pipelines to identify potential issues early and address them.

Update Regularly

When developing or maintaining your application, run composer update regularly and commit the composer.lock file whenever updates are made. This will ensure you are getting the latest bug fixes and security patches for the libraries you use.

Use the Composer Autoloader

We mentioned autoloading as a key feature of Composer. If you're new to Composer, all you need to do is add the following statement to the top of your script or application bootloader:

require 'vendor/autoload.php';
 
// or, if your application is in a subdirectory such as "public/":
require '../vendor/autoload.php';

This allows any code exposed in Composer packages to autoload within your application or script.

Final Thoughts

Composer is an immensely powerful and useful tool, and should be in every PHP developer's toolbox. We've only covered a very, very small number of its features and capabilities in this post — it can do a ton more, such as allow you to define project-specific and/or development-specific autoloaders, point to additional package repositories to consult during install operations, create automation scripts, and provide configuration for installation hooks. But at its core, and the reason it has become ubiquitous, is because it manages dependencies so well, and makes consuming them a single line in your code.

However, despite the many advantages that Composer has to offer, getting started using it for PHP dependency management can be a challenge, particularly when developer resources are tight or you don't have in-house PHP expertise at the ready. That's where Zend can help, from assisting in PHP dependency management during migration or modernization projects to providing fully custom consulting tailored to your applications.

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Additional Resources

• White Paper - The Hidden Costs of PHP Upgrades
• On-Demand Webinar - Managing Mission-Critical Web App Migrations
• Guide - Writing PHP Extensions
• Blog - Laravel Upgrades: Strategies and Approaches
• Blog - Best Practices for PHP Security
• Blog - A Developer's Guide to Building PHP APIs