# flow

> static type checker for javascript

**Wikidata**: [Q111269149](https://www.wikidata.org/wiki/Q111269149)  
**Source**: https://4ort.xyz/entity/flow-q111269149

## Summary
Flow is a static type checker for JavaScript developed by Meta (formerly Facebook). It is written in OCaml, released under the MIT License, and provides developers with compile‑time type safety for JavaScript codebases. The tool is actively maintained, with its latest stable release being 0.295.0 (2025‑12‑18).

## Key Facts
- Flow is a **software** product, specifically a static type checker for JavaScript.  
- It is **written in OCaml** and licensed under the **MIT License**.  
- The project is maintained by **Meta**, an American multinational technology corporation headquartered in Menlo Park, California.  
- Meta was founded on **2004‑07‑29** and employs thousands of people (e.g., 58,604 employees as of 2020‑12‑31).  
- Flow’s **website** is <https://flow.org/>.  
- The source code repository is hosted on GitHub at <https://github.com/facebook/flow>.  
- Flow’s **stable version** tag is **0.295.0**, released on **2025‑12‑18**.  
- The tool’s **Twitter handle** is @flowtype (ID 2878457194).  
- As of **2023‑02‑03**, the Twitter account had **11,641 followers**; as of **2022‑04‑12**, it had **11,955 followers**.  
- Flow’s **initial release** was **0.0.1** (not listed in the version history but implied by the first entry).  
- The project’s **development timeline** includes a continuous stream of releases from **0.117.0** (2020‑01‑24) to **0.295.0** (2025‑12‑18).  
- Flow is **copyrighted** and falls under the **copyright status** of “copyrighted.”  
- The tool is **categorized** under **instance_of: software**.  
- Flow’s **description** on Wikidata is “static type checker for javascript.”  
- The project is **open‑source** and hosted on GitHub under the **MIT License**.  
- Flow’s **stable releases** are marked with the qualifier **: stable version**.  
- The **latest stable release** (0.295.0) is the **preferred** version.  
- The project’s **source code repository** is identified by the property **: ** (GitHub) and **: ** (GitHub).  

## FAQs

**What is Flow and who created it?**  
Flow is a static type checker for JavaScript, created and maintained by Meta (formerly Facebook). It is written in OCaml and released under the MIT License.

**Which programming language is Flow written in?**  
Flow is implemented in **OCaml**, a functional programming language that extends Caml.

**What is the latest stable version of Flow?**  
The most recent stable release is **0.295.0**, published on **2025‑12‑18**.

**Where can I find Flow’s source code?**  
The source code is available on GitHub at <https://github.com/facebook/flow>.

**How active is Flow’s development?**  
Flow has a continuous release cadence, with new versions released roughly every month from 2020 through 2025, indicating active maintenance.

**Which license governs Flow?**  
Flow is distributed under the **MIT License**, allowing free use, modification, and distribution.

**Does Flow have a social media presence?**  
Yes, Flow maintains a Twitter account @flowtype, which had 11,955 followers in April 2022 and 11,641 followers in February 2023.

**What is Flow’s relationship with Meta?**  
Meta is the developer and maintainer of Flow, and the tool is part of Meta’s broader ecosystem of open‑source projects.

**Is Flow open source?**  
Yes, Flow’s source code is publicly available on GitHub and licensed under the MIT License.

**What platforms can Flow run on?**  
Flow is a command‑line tool that runs on any platform where OCaml can be compiled, typically Linux, macOS, and Windows.

## Why It Matters
Flow addresses a critical pain point in JavaScript development: the lack of static type safety in a language that is dynamically typed by default. By enabling developers to annotate types and catch type errors at compile time, Flow reduces runtime bugs, improves code quality, and enhances developer productivity. Its integration with popular editors and build systems allows seamless adoption in existing workflows. Flow’s open‑source nature and active maintenance by Meta have fostered a community of contributors and users, influencing the broader ecosystem of type‑checking tools such as TypeScript. The tool’s ability to interoperate with JavaScript and its incremental adoption model have made it a valuable asset for large codebases seeking gradual type migration.

## Notable For
- First major static type checker for JavaScript released by a major tech company (Meta).  
- Written in OCaml, distinguishing it from other type checkers that are typically written in JavaScript or TypeScript.  
- Maintained under an MIT License, encouraging widespread use and contribution.  
- Continuous release schedule with over 200 stable releases from 2020 to 2025.  
- Integration with Meta’s internal tooling and external editors (e.g., VS Code).  
- Provides a robust type inference engine that supports gradual typing.  
- Recognized by the community as a pioneering effort in JavaScript type safety.

## Body

### History
- Flow was first introduced by Meta (Facebook) as an internal tool to add static typing to JavaScript.  
- The earliest documented release in the provided data is **0.117.0** (2020‑01‑24).  
- Since then, Flow has released a new version approximately every month, with releases documented up to **0.295.0** (2025‑12‑18).  
- Each release is tagged on GitHub with a semantic version number and a release date.  
- The project’s development is tracked through GitHub releases, each containing a changelog and publication date.

### Development and Maintenance
- Meta is the sole listed developer and maintainer.  
- Meta’s corporate information: founded 2004‑07‑29, headquartered in Menlo Park, California, with a workforce ranging from 9,199 employees in 2014 to 58,604 in 2020.  
- Flow’s source code repository is hosted on GitHub under the Meta organization.  
- The repository is identified by the property **: ** (GitHub) and **: ** (GitHub).  
- The repository URL is <https://github.com/facebook/flow>.

### Licensing
- Flow is distributed under the **MIT License**, a permissive open‑source license that allows free use, modification, and distribution.  
- The license is explicitly listed in the structured properties.

### Technical Details
- **Programming Language**: OCaml, an extension of the Caml family of functional languages.  
- **Type System**: Flow implements a static type checker that can infer types, support gradual typing, and provide type annotations for JavaScript code.  
- **Versioning**: Semantic versioning is used; stable releases are marked with the qualifier **: stable version**.  
- **Release Cadence**: Releases range from 0.117.0 (2020‑01‑24) to 0.295.0 (2025‑12‑18), with frequent minor and patch updates.  
- **Stable Releases**: The latest stable release is 0.295.0, which is also the preferred version in the dataset.

### Community and Adoption
- Flow’s Twitter account @flowtype has a follower count that has fluctuated from 11,955 (2022‑04‑12) to 11,641 (2023‑02‑03).  
- The project’s presence on GitHub indicates an active open‑source community, though specific contributor counts are not provided.  
- Flow is used by developers who prefer a type system that can be gradually introduced into existing JavaScript codebases.

### Related Projects and Ecosystem
- **OCaml**: Flow’s implementation language; OCaml is an extension of the Caml programming language, first conceived in 1996.  
- **Meta**: The parent organization that also develops other open‑source projects such as React, GraphQL, and PyTorch.  
- **TypeScript**: While not explicitly mentioned, Flow is often compared to TypeScript as an alternative static type checker for JavaScript.  

### Release History Highlights
- **0.117.0** – First documented release (2020‑01‑24).  
- **0.150.0** – Release on 2021‑04‑29.  
- **0.200.0** – Release on 2023‑02‑16.  
- **0.250.0** – Release on 2024‑10‑17.  
- **0.295.0** – Latest stable release on 2025‑12‑18.  

### Documentation and Resources
- Official website: <https://flow.org/> provides documentation, tutorials, and API references.  
- GitHub repository includes release notes, source code, and issue tracking.  

### Impact on the JavaScript Ecosystem
- Flow pioneered the concept of adding static typing to JavaScript in a way that could be incrementally adopted.  
- Its design influenced subsequent type systems and tooling, encouraging the adoption of type safety in large JavaScript codebases.  
- Flow’s open‑source nature and active maintenance by Meta have ensured its relevance in the evolving JavaScript landscape.  

### Future Outlook
- The release schedule suggests continued active development, with the next expected stable release following the pattern of monthly updates.  
- Meta’s ongoing commitment to Flow is evident through its continued investment in releases and community engagement.

## References

1. [Release 0.117.0. 2020](https://github.com/facebook/flow/releases/tag/v0.117.0)
2. [Release 0.117.1. 2020](https://github.com/facebook/flow/releases/tag/v0.117.1)
3. [Release 0.118.0. 2020](https://github.com/facebook/flow/releases/tag/v0.118.0)
4. [Release 0.119.0. 2020](https://github.com/facebook/flow/releases/tag/v0.119.0)
5. [Release 0.119.1. 2020](https://github.com/facebook/flow/releases/tag/v0.119.1)
6. [Release 0.120.0. 2020](https://github.com/facebook/flow/releases/tag/v0.120.0)
7. [Release 0.120.1. 2020](https://github.com/facebook/flow/releases/tag/v0.120.1)
8. [Release 0.121.0. 2020](https://github.com/facebook/flow/releases/tag/v0.121.0)
9. [Release 0.122.0. 2020](https://github.com/facebook/flow/releases/tag/v0.122.0)
10. [Release 0.123.0. 2020](https://github.com/facebook/flow/releases/tag/v0.123.0)
11. [Release 0.124.0. 2020](https://github.com/facebook/flow/releases/tag/v0.124.0)
12. [Release 0.125.0. 2020](https://github.com/facebook/flow/releases/tag/v0.125.0)
13. [Release 0.125.1. 2020](https://github.com/facebook/flow/releases/tag/v0.125.1)
14. [Release 0.126.0. 2020](https://github.com/facebook/flow/releases/tag/v0.126.0)
15. [Release 0.126.1. 2020](https://github.com/facebook/flow/releases/tag/v0.126.1)
16. [Release 0.127.0. 2020](https://github.com/facebook/flow/releases/tag/v0.127.0)
17. [Release 0.128.0. 2020](https://github.com/facebook/flow/releases/tag/v0.128.0)
18. [Release 0.129.0. 2020](https://github.com/facebook/flow/releases/tag/v0.129.0)
19. [Release 0.130.0. 2020](https://github.com/facebook/flow/releases/tag/v0.130.0)
20. [Release 0.131.0. 2020](https://github.com/facebook/flow/releases/tag/v0.131.0)
21. [Release 0.132.0. 2020](https://github.com/facebook/flow/releases/tag/v0.132.0)
22. [Release 0.133.0. 2020](https://github.com/facebook/flow/releases/tag/v0.133.0)
23. [Release 0.134.0. 2020](https://github.com/facebook/flow/releases/tag/v0.134.0)
24. [Release 0.135.0. 2020](https://github.com/facebook/flow/releases/tag/v0.135.0)
25. [Release 0.136.0. 2020](https://github.com/facebook/flow/releases/tag/v0.136.0)
26. [Release 0.137.0. 2020](https://github.com/facebook/flow/releases/tag/v0.137.0)
27. [Release 0.138.0. 2020](https://github.com/facebook/flow/releases/tag/v0.138.0)
28. [Release 0.139.0. 2020](https://github.com/facebook/flow/releases/tag/v0.139.0)
29. [Release 0.140.0. 2020](https://github.com/facebook/flow/releases/tag/v0.140.0)
30. [Release 0.141.0. 2020](https://github.com/facebook/flow/releases/tag/v0.141.0)
31. [Release 0.142.0. 2021](https://github.com/facebook/flow/releases/tag/v0.142.0)
32. [Release 0.143.0. 2021](https://github.com/facebook/flow/releases/tag/v0.143.0)
33. [Release 0.143.1. 2021](https://github.com/facebook/flow/releases/tag/v0.143.1)
34. [Release 0.144.0. 2021](https://github.com/facebook/flow/releases/tag/v0.144.0)
35. [Release 0.145.0. 2021](https://github.com/facebook/flow/releases/tag/v0.145.0)
36. [Release 0.146.0. 2021](https://github.com/facebook/flow/releases/tag/v0.146.0)
37. [Release 0.147.0. 2021](https://github.com/facebook/flow/releases/tag/v0.147.0)
38. [Release 0.148.0. 2021](https://github.com/facebook/flow/releases/tag/v0.148.0)
39. [Release 0.149.0. 2021](https://github.com/facebook/flow/releases/tag/v0.149.0)
40. [Release 0.150.0. 2021](https://github.com/facebook/flow/releases/tag/v0.150.0)
41. [Release 0.150.1. 2021](https://github.com/facebook/flow/releases/tag/v0.150.1)
42. [Release 0.151.0. 2021](https://github.com/facebook/flow/releases/tag/v0.151.0)
43. [Release 0.152.0. 2021](https://github.com/facebook/flow/releases/tag/v0.152.0)
44. [Release 0.153.0. 2021](https://github.com/facebook/flow/releases/tag/v0.153.0)
45. [Release 0.154.0. 2021](https://github.com/facebook/flow/releases/tag/v0.154.0)
46. [Release 0.155.0. 2021](https://github.com/facebook/flow/releases/tag/v0.155.0)
47. [Release 0.155.1. 2021](https://github.com/facebook/flow/releases/tag/v0.155.1)
48. [Release 0.156.0. 2021](https://github.com/facebook/flow/releases/tag/v0.156.0)
49. [Release 0.157.0. 2021](https://github.com/facebook/flow/releases/tag/v0.157.0)
50. [Release 0.158.0. 2021](https://github.com/facebook/flow/releases/tag/v0.158.0)