projectjson

Projectjson is a former project configuration format used by early versions of the .NET Core tooling to describe a project's dependencies, target frameworks, and various build and runtime options. Introduced for the .NET Core SDK workflow, projectjson was designed to simplify dependency management and enable more rapid iteration with the dotnet command-line interface.

A project.json file, typically placed at the root of a project, is written in JSON and includes sections such as dependencies, frameworks, version, and buildOptions. The dependencies section lists NuGet packages by identity and version, while frameworks declares one or more target frameworks (for example, netcoreapp1.0 or netstandard1.6). Additional sections could specify runtime identifiers, packaging details, or custom build settings. During development, a corresponding lock file (project.lock.json) could be generated to record exact dependency versions for consistent restores.

Usage of projectjson was tied to the .NET Core CLI tooling, which used commands like dotnet restore, dotnet build, and dotnet run to manage projects. The format aimed to provide a more streamlined alternative to the traditional MSBuild-based .csproj format for smaller, cross-platform .NET Core projects.

Decline and replacement: In 2017, Microsoft announced that projectjson would be retired in favor of the SDK-style .csproj format. The new approach retained the ability to declare dependencies and target frameworks but did so within an evolving csproj schema that integrated with the broader MSBuild system. Migration tools and guidance were provided, and over time the tooling ecosystem shifted to the SDK-style csproj as the standard for .NET Core and later .NET projects. Today, projectjson is considered legacy, with new projects using the modern csproj format.