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Data oracles are WebAssembly (WASM) components that fetch or compute external data at evaluation time. The Newton network executes your WASM, and the output is fed into your Rego policy as data.data.

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What is a Data Oracle?

A data oracle is a JavaScript (or Rust/Python) program compiled to WASM that:
  1. Receives input arguments (wasm_args) as a JSON string
  2. Optionally fetches external data via HTTP
  3. Returns a JSON string that becomes available to your Rego policy as data.data

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WIT Interface

Every data oracle implements the newton-provider WIT (WebAssembly Interface Types) contract. Create newton-provider.wit: 
package newton:provider@0.1.0;

interface http {
    record http-request {
        url: string,
        method: string,
        headers: list<tuple<string, string>>,
        body: option<list<u8>>,
    }

    record http-response {
        status: u16,
        headers: list<tuple<string, string>>,
        body: list<u8>,
    }

    fetch: func(request: http-request) -> result<http-response, string>;
}

world newton-provider {
    import http;
    export run: func(input: string) -> result<string, string>;
}
The http import provides the fetch function for making HTTP requests from within the WASM sandbox. The run export is your oracle’s entry point.

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Implement in JavaScript

Create policy.js: 
export function run(wasm_args) {
  const args = JSON.parse(wasm_args);

  // Example: fetch an external API
  const response = httpFetch({
    url: `https://api.example.com/data?symbol=${args.base_symbol}`,
    method: "GET",
    headers: [["Accept", "application/json"]],
    body: null,
  });

  if (response.status !== 200) {
    return JSON.stringify({ error: "API request failed" });
  }

  const body = JSON.parse(
    new TextDecoder().decode(new Uint8Array(response.body))
  );

  return JSON.stringify({
    price: body.price,
    symbol: args.base_symbol,
    timestamp: Date.now(),
  });
}
The httpFetch function is provided by the Newton WASM runtime — you do not need to import it. It maps to the http.fetch function defined in the WIT interface.

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Build WASM

Compile the JavaScript into a WASM component using jco: 
# Install jco globally (if not already)
npm install -g @bytecodealliance/jco @bytecodealliance/componentize-js

# Build the WASM component
jco componentize -w newton-provider.wit -o policy.wasm policy.js \
  -d stdio random clocks http fetch-event
This produces policy.wasm in the current directory.
If you installed jco locally (without -g), run it via npx jco componentize ... instead.

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Test Locally

Test your WASM oracle before deploying: 
# Simulate with empty args
newton-cli policy-data simulate --wasm-file policy.wasm --input-json '{}'

# Simulate with specific args
newton-cli policy-data simulate \
  --wasm-file policy.wasm \
  --input-json '{"base_symbol": "BTC"}'
You can also test via the Gateway RPC: 
curl -X POST https://gateway-avs.sepolia.newt.foundation/rpc \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer <your_api_key>" \
  -d '{
    "jsonrpc": "2.0",
    "method": "newt_simulatePolicyData",
    "params": {
      "policy_data_address": "0x...",
      "wasm_args": "0x7b22626173655f73796d626f6c223a22425443227d"
    },
    "id": 1
  }'

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Alternative Languages

While JavaScript is the most common choice, you can also write data oracles in: All languages compile to the same WIT interface and produce interchangeable WASM components.

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Next Steps

Writing Policies

Write a Rego policy that uses your oracle’s output

Deploying with CLI

Deploy your oracle and policy to IPFS and on-chain