oso is an open source policy engine for authorization that’s embedded in your application. It provides a declarative policy language for expressing authorization logic. You define this logic separately from the rest of your application code, but it executes inside the application and can call directly into it. oso ships as a library with a built-in debugger and REPL.

oso is ideal for building permissions into user-facing applications, but you can check out docs to learn about other applications for oso.

Programming language: Rust
License: Apache License 2.0
Latest version: v0.9.0

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Development GitHub release (latest SemVer) Go version Maven version NPM version PyPI version RubyGems version Crates.io version Slack

What is Oso?

Oso is a batteries-included framework for building authorization in your application.

With Oso, you can:

  • Model: Set up common permissions patterns like role-based access control (RBAC) and relationships using Oso’s built-in primitives. Extend them however you need with Oso’s declarative policy language, Polar.
  • Filter: Go beyond yes/no authorization questions. Implement authorization over collections too - e.g., “Show me only the records that Juno can see.”
  • Test: Write unit tests over your authorization logic now that you have a single interface for it. Use the Oso debugger or REPL to track down unexpected behavior.

Oso offers libraries for Node.js, Python, Go, Rust, Ruby, and Java.

Our latest creation Oso Cloud makes authorization across services as easy as oso.authorize(user, action, resource). Learn about it.


Community & Support

If you have any questions on Oso or authorization more generally, you can join our engineering team & hundreds of other developers using Oso in our community Slack:


Share your story

We'd love to hear about your use case and experience with Oso. Share your story in our Success Stories issue or fill out this form for some Oso swag.



Oso's Rust core is developed against Rust's latest stable release.

Language libraries

Oso's language libraries can be developed without touching the Rust core, but you will still need the Rust stable toolchain installed in order to build the core.

To build the WebAssembly core for the Node.js library, you will need to have wasm-pack installed and available on your system PATH.

Language requirements

To work on a language library, you will need to meet the following version requirements:

  • Java: 10+
    • Maven: 3.6+
  • Node.js: 12.20.0+
    • Yarn 1.22+
  • Python: 3.7+
  • Ruby: 2.4+
    • Bundler 2.1.4+
  • Rust: 1.46+
  • Go: 1.14+

Contributing & Jobs


If you want to work on the Oso codebase full-time, visit our jobs page.



*Note that all licence references and agreements mentioned in the oso README section above are relevant to that project's source code only.