11 releases (6 breaking)

new 0.11.0 Feb 23, 2021
0.10.0 Jan 19, 2021
0.9.0 Dec 9, 2020
0.8.2 Nov 25, 2020
0.1.0 Jan 28, 2019
Download history 26/week @ 2020-11-06 12/week @ 2020-11-13 41/week @ 2020-11-20 24/week @ 2020-11-27 40/week @ 2020-12-04 9/week @ 2020-12-11 17/week @ 2020-12-18 3/week @ 2020-12-25 15/week @ 2021-01-01 146/week @ 2021-01-08 489/week @ 2021-01-15 214/week @ 2021-01-22 277/week @ 2021-01-29 230/week @ 2021-02-05 182/week @ 2021-02-12 103/week @ 2021-02-19

562 downloads per month


13K SLoC


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What is Oso?

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 Use Cases to learn about other applications for Oso.

Using Oso consists of two parts:

  1. Writing Oso policies in a declarative policy language called Polar.
  2. Embedding Oso in your application using the appropriate language-specific authorization library.

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

Getting started

To get up and running with Oso, check out the Getting Started guides in the Oso documentation.



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: 10.14.2+
    • Yarn 1.22+
  • Python: 3.6+
  • Ruby: 2.4+
    • Bundler 2.1.4+
  • Rust: 1.46+
  • Go: 1.12+






~127K SLoC