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composer.json is a JSON file placed in the root folder of PHP project. Its purpose is to specify a common project properties, meta data and dependencies, and it is a part of vast array of existing projects. In most ways, it is a counterpart to .NET project file. At least, the information from the composer.json file can be represented by standard .NET project properties and items (not the other way around).


By default, the composer.json file is processed during build time. As a result, certain composer metadata is mapped to the corresponding project properties, thanks to which the created NuGet packages are automatically annotated.

Following table lists composer meta and corresponding project properties being automatically set:

Meta MsBuild Property Nuspec Value
"name" PackageId Id
"description" PackageDescription Description
"version" Version, PackageVersion /1/ Version
"license" PackageLicenseExpression license
"homepage" PackageProjectUrl ProjectUrl
"authors" Authors Authors

/1/ Version respects specified $(VersionSuffix) property. In case project has non-empty VersionSuffix, the resulting Version will have the suffix specified even composer's version meta does not have it.

MSBuild Properties#


The ComposerJsonPath property controls path to the composer.json file. If the property is empty, the file is being located next to the project file implicitly.


Set ComposerJsonPath to false in order to disable processing of composer.json meta data during build.


Setting ComposerAutoload to true or false controls whether autoload rules are processed.


Explicitly setting VersionSuffix allows to override suffix portion of version meta data from composer file. If VersionSuffix is non-empty string, the resulting version will respect the suffix.

Project file:



    "version": "1.2.3"

The setup above results in PackageVersion property set to 1.2.3-dev.

Composer Dependencies#

Sections "require", "require-dev" and "suggest" are not processed (yet).

Composer Autoload#

Available since 0.9.980

Composer autoloading provides a standard approach in defining what classes will be loaded automatically when needed. Also, it allows to specify what files will be included by the runtime at the very beginning of request or the program start. When the compiler processes the "autoload" section, it remembers the autoloading rules and stores the information in metadata. It does not use the information to compile any additional files - all the files meant to be compiled have to be listed within the <Compile> MSBuild item group explicitly.

  • Rules from composer.json will be stored within the assembly metadata; hence the original composer.json file is not required to be bundled with the compiled application.
  • Files listed in "autoload" are not automatically added to the compilation. Files needed to be compiled have to be listed within the <Compile> item group explicitly.
  • A syntax error in the json file will cause the compilation to stop with a corresponding error message. A wrong value in the composer.json causes a compile-time warning and the compilation will continue.

Sample "composer.json":

    "autoload": {
        "psr-4": {
            "Vendor\\Namespace\\": "src/",
            "": "src/",
        "psr-0": {
            "Vendor\\Namespace\\": "src/",
            "Vendor_Namespace_": "src/"
        "classmap": ["src/", "lib/", "Something.php"],
        "exclude-from-classmap": ["/src/Tests/", "/lib/tests/"],
        "files": [],

During the compilation, this information is used in order to avoid autoloading process in the first place. Classes, interfaces and traits fulfiling the specified rules are declared implicitly without need of invoking autoloaders during run time. (We can say, the autoloading will performed only once during compilation when it's safe to.) In case a source file contains more than just the class itself, autoloading cannot be fully optimized. In such case, containing source file has to be looked up and invoked during run time causing an unnecesary overhead.

This behavior differs from standard PHP where the map above is used to generate autoloaders which are invoked every time when an unknown class, interface or trait is being used in every new web request.