WASI is a standardization effort that defines a set of system interface APIs for WebAssembly applications.
WASI addresses the need for WebAssembly programs to interact with operating system functionality in a portable, standardized way. Rather than each WebAssembly runtime implementing its own system interface, WASI provides a common set of APIs inspired by POSIX and CloudABI. The project has evolved through multiple preview versions, moving from the witx IDL format used in Preview 1 to the more modular Wit IDL in Preview 2, and most recently to Preview 3, which leverages the component model's native async functionality through future and stream types. Individual API proposals are developed in separate repositories, with this main repository serving as a coordination point for general discussion, documentation of working practices, and high-level goals.
Developers considering WASI adoption should understand that it is a standards effort rather than a single implementation. Preview 1 is widely deployed and stable, making it suitable for production use cases that can accept its design constraints. Preview 2 and Preview 3 offer improved modularity and expressiveness for new projects, though they represent evolving standards. The project provides a proposal template and contributing guide for those wishing to extend WASI with new APIs. The work is organized around individual API repositories rather than centralized in this location, so adopters should expect to engage with multiple repositories depending on which APIs they need.
The project maintains active engagement with its user base, with nearly all open issues originating from external users rather than the core team, demonstrating substantial real-world adoption. Maintainers respond to new issues and pull requests within a day. The issue tracker shows concentrated activity around three areas: inactive proposals, HTTP APIs, and filesystem APIs, indicating where the community is focusing standardization efforts.
