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Top 23 C# API Projects
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Bitwarden - Open-source password manager.
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Stream
Stream - Scalable APIs for Chat, Feeds, Moderation, & Video. Stream helps developers build engaging apps that scale to millions with performant and flexible Chat, Feeds, Moderation, and Video APIs and SDKs powered by a global edge network and enterprise-grade infrastructure.
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Project mention: Netflix will show generative AI ads midway through streams in 2026 | news.ycombinator.com | 2025-05-15
https://github.com/Jackett/Jackett | https://github.com/qbittorrent/search-plugins/wiki/How-to-co...
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.NET 9 will absolutely load a library that was built targeting .NET 5.
For instance, GraphQL was built targeting both .NET 5 and .NET Standard 2.0, as you can see towards the top of the NuGet page: https://www.nuget.org/packages/GraphQL
.NET 9 will use the .NET 5 build, not .NET Standard 2.0. (.NET Framework 4.8.x would use .NET Standard 2.0.) Because .NET 5 > .NET Standard 2.0.
Or Automapper 14 targets only .NET 8: https://www.nuget.org/packages/AutoMapper
It runs on .NET 9 and .NET 10.
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Hot Chocolate
Welcome to the home of the Hot Chocolate GraphQL server for .NET, the Strawberry Shake GraphQL client for .NET and Nitro the awesome Monaco based GraphQL IDE.
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InfluxDB
InfluxDB – Built for High-Performance Time Series Workloads. InfluxDB 3 OSS is now GA. Transform, enrich, and act on time series data directly in the database. Automate critical tasks and eliminate the need to move data externally. Download now.
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ASP.NET MVC Boilerplate
.NET project templates with batteries included, providing the minimum amount of code required to get you going faster.
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Project mention: My new hobby: watching AI slowly drive Microsoft employees insane | news.ycombinator.com | 2025-05-21
Yes but the improvements are very gradual. It takes years for something to reach maturity. At least for the web stuff which is what I know of.
Eg:
Minimal APIs were released in 2021 but it won't be until .NET 10 that they will have validation. Amazing that validation was not a day one priority for an API. I'm not certain if even in .NET 10 Minimal APIs will have full parity of features with MVC.
Minification of static assets didn't come until .NET 9 released in 2024. This was already commonplace in the JS world a decade earlier. It could have been a quick win so long ago for .NET web apps.
Blazor was released in 2018. 7 years later they still haven't fixed plenty of circuit reconnection issues. They are working on it but progress is also quite slow. Supposedly with .NET 10 session state will be able to be persist etc but it remains to be seen.
OpenAPI is also hit and miss. Spec v3.1 released in 2021 is still not supported. Supposedly it will come with .NET 10.
Not from .NET but they have a project called Kiota for generating clients from OpenAPI specs. It's unusable because of this huge issue that makes all properties in a type nullable. It's been open since 2023. [1]
Etc.
[1] https://github.com/microsoft/kiota/issues/3911
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ChatGPT
A ChatGPT C# client for MacOS, Windows, Linux, Android, iOS and Browser. Powered by Avalonia UI framework. (by wieslawsoltes)
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FFImageLoading - Fast & Furious Image Loading
Image loading, caching & transforming library for Xamarin and Windows
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data-api-builder
Data API builder provides modern REST and GraphQL endpoints to your Azure Databases and on-prem stores.
Project mention: Directus – real-time REST and GraphQL API of any SQL database | news.ycombinator.com | 2025-02-23That looks really interesting, but maybe only useful for mssql? [1]
[1] https://github.com/azure/data-api-builder/labels/known-issue
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Project mention: log4net VS Serilog - a user suggested alternative | libhunt.com/r/log4net | 2025-06-09
Redirect the obsolete to the official: https://www.libhunt.com/r/logging-log4net
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JsonApiDotNetCore
A framework for building JSON:API compliant REST APIs using ASP.NET and Entity Framework Core.
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Project mention: These 20 Awesome API Clients Will Change How You Work with APIs | dev.to | 2025-06-11
Pororoca is a network debugging tool focused on HTTP/2 and HTTP/3 support, making it ideal for developers exploring newer web protocols.
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SaaSHub
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NOTE:
The open source projects on this list are ordered by number of github stars.
The number of mentions indicates repo mentiontions in the last 12 Months or
since we started tracking (Dec 2020).
C# API discussion
C# API related posts
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Extending Methods in WebForms Core
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CodeBehind Turns Two Years Old
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CodeBehind 4.2 Released
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WebForms Core Organization on GitHub
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log4net VS Serilog - a user suggested alternative
3 projects | 9 Jun 2025 -
Migrating from WebForms to WebForms Core
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Creating an FAQ Page Without JavaScript
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A note from our sponsor - SaaSHub
www.saashub.com | 18 Jul 2025
Index
What are some of the best open-source API projects in C#? This list will help you:
| # | Project | Stars |
|---|---|---|
| 1 | Bitwarden | 16,844 |
| 2 | Jackett | 13,624 |
| 3 | GraphQL for .NET | 5,946 |
| 4 | Hot Chocolate | 5,522 |
| 5 | ServiceStack | 5,468 |
| 6 | tModLoader | 4,622 |
| 7 | DocFX | 4,298 |
| 8 | ASP.NET MVC Boilerplate | 3,457 |
| 9 | Telegram.Bot | 3,440 |
| 10 | kiota | 3,429 |
| 11 | ApiEndpoints | 3,182 |
| 12 | simulator | 2,372 |
| 13 | ChatGPT | 1,469 |
| 14 | FFImageLoading - Fast & Furious Image Loading | 1,415 |
| 15 | DSharpPlus | 1,297 |
| 16 | data-api-builder | 1,115 |
| 17 | Mobius: C# API for Spark | 940 |
| 18 | Log4Net | 898 |
| 19 | WebAPI Contrib | 767 |
| 20 | JsonApiDotNetCore | 705 |
| 21 | Twilio-csharp | 693 |
| 22 | WatsonTcp | 633 |
| 23 | Pororoca | 594 |
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