head to head · open source
fastapi vs greenmail
fastapi has 102,402 GitHub stars, 9,903 forks, 78 open issues and last shipped 4 days ago. greenmail has 744 stars, 204 forks, 67 open issues and last shipped yesterday. fastapi leads on adoption by 13,664% (102,402 vs 744 stars). fastapi is written in Python under MIT; greenmail is written in Java under Apache-2.0. fastapi has attracted 10% as many forks as stars, greenmail 27%. greenmail was the more recently maintained of the two, and both are self-hostable with no licence fee.
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 8884 open source comparisons
Side by side
| fastapi | greenmail | |
|---|---|---|
| GitHub stars | ★ 102K | ★ 744 |
| License | MIT | Apache-2.0 |
| Written in | Python | Java |
| Last push | 2026-09-14 | 2026-09-17 |
| Forks | ⑂ 9.9K | ⑂ 204 |
| 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 greenmail if
- You want the greenmail feature set and don't need the biggest community
- You prefer the Apache-2.0 license terms
- Your stack matches Java
- You evaluated both and greenmail 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 greenmail
GreenMail is a Java project that provides a virtual mail server for testing email based applications, services, and systems. It is Apache 2.0 licensed, published through Maven Central as com.icegreen:greenmail, and listed in Developer Tools / API Development & Testing.
read the full greenmail 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 greenmail more popular?
fastapi has 102,402 GitHub stars and greenmail has 744. fastapi has the larger community by that measure.
Are fastapi and greenmail free?
Both are open source. fastapi is licensed under MIT and greenmail under Apache-2.0. Neither carries a licence fee.
What is the difference between fastapi and greenmail?
fastapi is written in Python and greenmail in Java. 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 greenmail?
Choose fastapi if you want the larger community (102,402 stars) or its MIT licence terms. Choose greenmail if its feature set, stack or Apache-2.0 licence fits better. Both are self-hostable.