I am not a lawyer. If you want legal advice, talk with a lawyer.
Here is the license for the C# compiler (Roslyn):
https://github.com/dotnet/roslyn/blob/master/License.txt
The license is an MIT which means that you should be able to fork the language and do anything you want with it.
The names "C#" and ".NET" are Microsoft trademarks and so you would need to use some other name
In Ask HN: Can I legally fork C# and share my new version?dotnet
roslyn
C#2015–2026
dotnet / roslyn
roslyn
The Roslyn .NET compiler provides C# and Visual Basic languages with rich code analysis APIs.
115Distinct people
143Mentions
1Explicit recommenders
20.8KGitHub stars
What to know before exploring
What it is
The Roslyn .NET compiler provides C# and Visual Basic languages with rich code analysis APIs.
GitHub
Where it is used
No documented product use was verified in the last source check.
What people are saying
> - I love that they are adding REPL. I really wish C# had this Here you go :) https://github.com/dotnet/roslyn/wiki/C%23-Interactive-Walkt... Also: csi.exe. Try it :)
josteink used a recommendation phrase. One indexed comment matches. This is a phrase match, not a verdict.
No classified warning is attached to this page. Read the discussions before treating silence as approval.
Also in these discussions
- dotnet/coreclr · linked in 4 of the same discussions
- dotnet/corefx · linked in 3 of the same discussions
- dotnet/core · linked in 2 of the same discussions
Mentioned in the same Hacker News threads. That is not proof they are substitutes.
This week on Hacker News
Nov 8–Nov 15 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/15/2026, 12:45:45 PM UTC.
No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.
Mentions over time
HN mentions by year143 dated mentions
Observed mentions: 2015-01-14 23:49:47 UTC to 2026-05-11 08:56:48 UTC.
* An incomplete calendar period is marked with an outlined bar. Its count is not directly comparable with a full period.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
View mention counts and date ranges
| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2015 | 2015-01-01 00:00:00 UTC | 2016-01-01 00:00:00 UTC | 32 | 6 | 26 |
| 2016 | 2016-01-01 00:00:00 UTC | 2017-01-01 00:00:00 UTC | 28 | 6 | 22 |
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 26 | 2 | 24 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 6 | 1 | 5 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 6 | 0 | 6 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 12 | 0 | 12 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 4 | 0 | 4 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 3 | 1 | 2 |
| 2024 | 2024-01-01 00:00:00 UTC | 2025-01-01 00:00:00 UTC | 11 | 1 | 10 |
| 2025 | 2025-01-01 00:00:00 UTC | 2026-01-01 00:00:00 UTC | 8 | 0 | 8 |
| 2026 (partial) | 2026-01-01 00:00:00 UTC | 2027-01-01 00:00:00 UTC | 6 | 1 | 5 |
From the project README
An excerpt from the repository, fetched Nov 13, 2026.
Read the project’s introduction
The .NET Compiler Platform
Roslyn is the open-source implementation of both the C# and Visual Basic compilers with an API surface for building code analysis tools.
C# and Visual Basic Language Feature Suggestions
If you want to suggest a new feature for the C# or Visual Basic languages go here:
dotnet/csharplang for C# specific issues
dotnet/vblang for VB-specific features
dotnet/csharplang for features that affect both languages
Contributing
All work on the C# and Visual Basic compiler happens directly on GitHub. Both core team members and external contributors send pull requests which go through the same review process.
If you are interested in fixing issues and contributing directly to the code base, a great way to get started is to ask some questions on GitHub Discussions! Then check out our contributing guide which covers the following:
Coding guidelines
The development workflow, including debugging and running tests
Submitting pull requests
Finding a bug to fix in the IDE or Compiler
Finding a feature to implement in the IDE or Compiler
Roslyn API suggestions should go through the API review process
Community
The Roslyn community can be found on GitHub Discussions, where you can ask questions, voice ideas, and share your projects.
To chat with other community members, you can join the Roslyn channel on the CSharp Community Discord.
Our Code of Conduct applies to all Roslyn community channels and has adopted the .NET Foundation Code of Conduct.
Documentation
Visit Roslyn Architecture Overview to get started with Roslyn’s API’s.
NuGet Feeds
The latest pre-release builds are available from the following public NuGet feeds:
Compiler: https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json
IDE Services: https://pkgs.dev.azure.com/azure-public/vside/_packaging/vssdk/nuget/v3/index.json
.NET SDK: https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json
Continuous Integration status
Builds
Branch
Windows Debug
Windows Release
Unix Debug
main
Desktop Unit Tests
Branch
Debug x86
Debug x64
Release x86
Release x64
main
CoreClr Unit Tests
Branch
Windows Debug
Windows Release
Linux
main
Integration Tests
Branch
Debug x86
Debug x64
Release x86
Release x64
main
Misc Tests
Branch
Determinism
Analyzers
Build Correctness
Source build
TODO/Prototype
Spanish
MacOS
main
.NET Foundation
This project is part of the .NET Foundation along with other projects like the .NET Runtime.
Read the full README on GitHub