dotnet/runtime

Analysis updated 2026-06-24

★ 17,883C#Audience · developerComplexity · 5/5LicenseSetup · hard

Mindmap

mindmap
  root((dotnet runtime))
    What it does
      Executes .NET code
      Base class libraries
      Installer tooling
    Tech stack
      C#
      C C++
      MSBuild
    Audience
      Runtime contributors
      Performance engineers
      Microsoft devs
    Use cases
      Fix runtime bugs
      Improve performance
      Test nightly builds
    License
      MIT permissive

mindmap root((dotnet runtime)) What it does Executes .NET code Base class libraries Installer tooling Tech stack C# C C++ MSBuild Audience Runtime contributors Performance engineers Microsoft devs Use cases Fix runtime bugs Improve performance Test nightly builds License MIT permissive

Click or tap to explore — scroll the page freely

What do people build with it?

USE CASE 1

Contribute a bug fix or performance improvement to the .NET runtime.

USE CASE 2

Build the runtime from source to test an unreleased change in your own app.

USE CASE 3

Read the base class libraries to understand how .NET implements things like strings or sockets.

USE CASE 4

Pull a nightly build to try the latest language or runtime features early.

What is it built with?

C#C++MSBuild

How does it compare?

	dotnet/runtime	hellzerg/optimizer	ardalis/cleanarchitecture
Stars	17,883	18,159	18,171
Language	C#	C#	C#
Setup difficulty	hard	easy	moderate
Complexity	5/5	2/5	3/5
Audience	developer	vibe coder	developer

Figures from each repo's GitHub metadata at analysis time.

How do you get it running?

Difficulty · hard Time to first run · 1day+

Building the runtime from source is a heavyweight operation, needs lots of disk, build prerequisites and patience, most app developers should just install .NET normally.

MIT, use, modify and ship the code freely, including commercially, as long as you keep the copyright notice.

In plain English

This repository is the source code for the .NET Runtime, the core engine that makes .NET applications run. .NET is a software platform from Microsoft that lets developers build and run applications on many different kinds of hardware and operating systems, including cloud servers, mobile devices, desktop computers, and IoT (Internet of Things) devices. It is written primarily in C#. What this specific repository contains is the lowest-level infrastructure: the runtime itself (which executes your .NET code), the base class libraries (the built-in code that .NET programs can call, things like file handling, networking, data structures, and string operations), and the tools used to install and run .NET on a machine. This is not a library you import into a project, it is the underlying system that your .NET programs run on top of. Because this is such a fundamental piece of software, it is extremely large and complex, and contributing to it requires following detailed workflow instructions about how to build and test changes. The repository includes guidance for contributors, links to documentation, and instructions for getting nightly builds if you want to test unreleased changes in your own projects. You would browse or contribute to this repository if you are a developer working on the .NET platform itself, for example, fixing bugs in the runtime, improving performance of the base libraries, or adding new language features. Most .NET application developers never need to look here, they just use .NET through its official installer and tools. The project is open source under the MIT license and governed by the .NET Foundation.

Copy-paste prompts

Prompt 1

Walk me through cloning dotnet/runtime and building just the libraries subset on macOS, what prerequisites do I need?

Prompt 2

I want to fix a small bug in System.Text.Json. Where in dotnet/runtime does that code live and how do I run the unit tests for just that area?

Prompt 3

Explain how to install a nightly build of the .NET runtime alongside my stable install so I can test against both.

Prompt 4

Profile this C# function with the dotnet/runtime tools to see whether it's CPU- or GC-bound: <paste code here>.

Prompt 5

I'm new to runtime contribution. Read dotnet/runtime's contributing guide and give me a 'first PR' checklist a beginner can follow.

Frequently asked questions

What is runtime?

Source code for the .NET runtime and base class libraries, the low-level engine that actually executes .NET apps across servers, desktops, mobile and IoT.

What language is runtime written in?

Mainly C#. The stack also includes C#, C++, MSBuild.

What license does runtime use?

MIT, use, modify and ship the code freely, including commercially, as long as you keep the copyright notice.

How hard is runtime to set up?

Setup difficulty is rated hard, with roughly 1day+ to a first successful run.

Who is runtime for?

Mainly developer.

Open on GitHub → Explain another repo

This repo across BitVibe Labs

Scan in gitsafehub Deploy in gitdeployhub dotnet on gitmyhub

Verify against the repo before relying on details.