Open Policy Agent WebAssembly SDK

Usage no npm install needed!

<script type="module">
  import block65OpaWasm from 'https://cdn.skypack.dev/@block65/opa-wasm';


Work in Progress -- Contributions welcome!!

Open Policy Agent WebAssemby NPM Module

This is the source for the @open-policy-agent/opa-wasm NPM module which is a small SDK for using WebAssembly (wasm) compiled Open Policy Agent Rego policies.

Getting Started

Install the module

npm install @open-policy-agent/opa-wasm 


There are only a couple of steps required to start evaluating the policy.

Import the module

const { loadPolicy } = require("@open-policy-agent/opa-wasm");

Load the policy


The load_policy request returns a Promise with the loaded policy. Typically this means loading it in an async function like:

const policy = await loadPolicy(policyWasm)

Or something like:

loadPolicy(policyWasm).then(policy => {
    // evaluate or save the policy
}, error => {
    console.error("Failed to load policy: " + error)

The policyWasm needs to be either the raw byte array of the compiled policy wasm file, or a web assembly module.

For example:

const fs = require('fs');

const policyWasm = fs.readFileSync('policy.wasm');

Alternatively the bytes can be pulled in remotely from a fetch or in some cases (like CloudFlare Workers) the wasm binary can be loaded directly into the javascript context through external APIs.

Evaluate the Policy

The loaded policy object returned from loadPolicy() has a couple of important API's for policy evaluation:

setData(obj) -- Provide an external data document for policy evaluation. Requires a JSON serializable object. evaluate(input) -- Evaluates the policy using any loaded data and the supplied input document.

The input parameter must be a JSON string.


input = '{"path": "/", "role": "admin"}';

loadPolicy(policyWasm).then(policy => {
    resultSet = policy.evaluate(input);
    if (resultSet == null) {
        console.error("evaluation error")
    if (resultSet.length == 0) {
    console.log("allowed = " + allowed[0].result);
}).catch( error => {
    console.error("Failed to load policy: ", error);

For any opa build created WASM binaries the result set, when defined, will contain a result key with the value of the compiled entrypoint. See https://www.openpolicyagent.org/docs/latest/wasm/ for more details.

Writing the policy

See https://www.openpolicyagent.org/docs/latest/how-do-i-write-policies/

Compiling the policy

Either use the Compile REST API or opa build CLI tool.

For example, with OPA v0.20.5+:

opa build -t wasm -e 'example/allow' example.rego

Which is compiling the example.rego policy file with the result set to data.example.allow. The result will be an OPA bundle with the policy.wasm binary included. See ./examples for a more comprehensive example.

See opa build --help for more details.