head to head · open source
fastapi vs OpenAPI.NET
fastapi has 104,566 GitHub stars, 10,179 forks, 78 open issues and last shipped yesterday. OpenAPI.NET has 1,616 stars, 291 forks, 31 open issues and last shipped 6 days ago. fastapi leads on adoption by 6,371% (104,566 vs 1,616 stars). fastapi is written in Python under MIT; OpenAPI.NET is written in C# under MIT. fastapi has attracted 10% as many forks as stars, OpenAPI.NET 18%. fastapi was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 1 topic tag (openapi), so they are genuine substitutes rather than adjacent tools.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| fastapi | OpenAPI.NET | |
|---|---|---|
| GitHub stars | ★ 105K | ★ 1.6K |
| License | MIT | MIT |
| Written in | Python | C# |
| Last push | 2026-11-02 | 2026-10-28 |
| Forks | ⑂ 10K | ⑂ 291 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick fastapi if
- You weight community size — 105K stars and counting
- You want the MIT license terms
- Your stack matches Python
- You value the larger contributor base for long-term maintenance
pick OpenAPI.NET if
- You want the OpenAPI.NET feature set and don't need the biggest community
- You prefer the MIT license terms
- Your stack matches C#
- You evaluated both and OpenAPI.NET fits your workflow better
About fastapi
FastAPI framework, high performance, easy to learn, fast to code, ready for production Documentation : Source Code : FastAPI is a modern, fast (high performance), web framework for building APIs with Python based on standard Python type hints. The key features are: Fast : Very high performance, on par with NodeJS and Go (thanks to Starlette and Pydantic). One of the fastest Python frameworks available. Fast to code : Increase the speed to develop features by about 200% to 300%. Fewer bugs : Reduce about 40% of human (developer) induced errors. Intuitive : Great editor support. Completion everywhere. Less time…
read the full fastapi overview →
About OpenAPI.NET
OpenAPI.NET The OpenAPI.NET SDK contains a useful object model for OpenAPI documents in .NET along with common serializers to extract raw OpenAPI JSON and YAML documents from the model. See more information on the OpenAPI specification and its history here: OpenAPI Initiative Project Objectives: Provide a single shared object model in .NET for OpenAPI descriptions. Include the most primitive Reader for ingesting OpenAPI JSON and YAML documents in both V2 and V3 formats. Provide OpenAPI description writers for both V2 and V3 specification formats. Enable developers to create Readers that translate different data…
read the full OpenAPI.NET overview →
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Frequently asked questions
Is fastapi or OpenAPI.NET more popular?
fastapi has 104,566 GitHub stars and OpenAPI.NET has 1,616. fastapi has the larger community by that measure.
Are fastapi and OpenAPI.NET free?
Both are open source. fastapi is licensed under MIT and OpenAPI.NET under MIT. Neither carries a licence fee.
What is the difference between fastapi and OpenAPI.NET?
fastapi is written in Python and OpenAPI.NET in C#. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, fastapi or OpenAPI.NET?
Choose fastapi if you want the larger community (104,566 stars) or its MIT licence terms. Choose OpenAPI.NET if its feature set, stack or MIT licence fits better. Both are self-hostable.