head to head · open source
fastapi vs OpenAPI.NET
fastapi has 102,428 GitHub stars, 9,909 forks, 78 open issues and last shipped 5 days ago. OpenAPI.NET has 1,610 stars, 286 forks, 31 open issues and last shipped 2 days ago. fastapi leads on adoption by 6,262% (102,428 vs 1,610 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%. OpenAPI.NET 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.
← all 15422 open source comparisons
Side by side
| fastapi | OpenAPI.NET | |
|---|---|---|
| GitHub stars | ★ 102K | ★ 1.6K |
| License | MIT | MIT |
| Written in | Python | C# |
| Last push | 2026-09-14 | 2026-09-17 |
| Forks | ⑂ 9.9K | ⑂ 286 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick fastapi if
- You weight community size — 102K 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 is an MIT licensed, high performance Python web framework for building APIs with standard Python type hints, aimed at Python developers and teams that need production ready HTTP services with automatic OpenAPI documentation.
read the full fastapi overview →
About OpenAPI.NET
OpenAPI.NET is the Microsoft maintained .NET SDK that provides a shared object model for OpenAPI descriptions, together with readers and writers that convert OpenAPI JSON and YAML documents into and out of that model, and it is aimed at C and .NET developers who build, validate, or transform OpenAPI documents in code.
read the full OpenAPI.NET overview →
More in Developer Tools
Related comparisons
More API Development & Testing projects
Compare either of these against the rest of the API Development & Testing field.
Frequently asked questions
Is fastapi or OpenAPI.NET more popular?
fastapi has 102,428 GitHub stars and OpenAPI.NET has 1,610. 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 (102,428 stars) or its MIT licence terms. Choose OpenAPI.NET if its feature set, stack or MIT licence fits better. Both are self-hostable.