Somnia Agents / Base agents

JSON API Request

Fetch JSON from any public API and extract a value with a selector path.

Fetches JSON data from any public API endpoint and extracts specific values using a selector path. This agent is the fundamental building block for creating on-chain oracles.

Per-agent price: 0.0003 SOMI (STT on testnet). See Gas fees.

Methods

Function	Inputs	Output	Use case
`fetchString`	url, selector	string	Text values, names
`fetchUint`	url, selector, decimals	uint256	Prices, positive numbers
`fetchInt`	url, selector, decimals	int256	Temperatures, signed numbers
`fetchBool`	url, selector	bool	Flags, status checks
`fetchStringArray`	url, selector	string[]	Lists of names/IDs
`fetchUintArray`	url, selector, decimals	uint256[]	Price lists, numeric arrays

Parameters

Input	Type	Description
`url`	string	The URL of the JSON API endpoint to fetch
`selector`	string	A dot-notation path to extract from the response (e.g., `data.price` or `items[0].name`)
`decimals`	uint8	Number of decimal places to scale the value by (multiplies by 10^decimals)

Decimal scaling

The decimals parameter is used by fetchUint, fetchInt, and fetchUintArray to convert floating-point values from APIs into blockchain-compatible integers. The value is multiplied by 10^decimals.

For example, with decimals=8:

42000.50 becomes 4200050000000
0.00001234 becomes 1234

This follows the standard pattern for handling decimals in smart contracts (e.g., ERC-20 tokens typically use 18 decimals).

Method signatures

function fetchString(string url, string selector) returns (string)
function fetchUint(string url, string selector, uint8 decimals) returns (uint256)
function fetchInt(string url, string selector, uint8 decimals) returns (int256)
function fetchBool(string url, string selector) returns (bool)
function fetchStringArray(string url, string selector) returns (string[])
function fetchUintArray(string url, string selector, uint8 decimals) returns (uint256[])

Example use cases

Fetching cryptocurrency prices from CoinGecko or similar APIs
Retrieving weather data for parametric insurance contracts
Pulling sports scores for prediction markets
Accessing any REST API that returns JSON

Usage examples

Fetch a price as uint256

import { encodeFunctionData } from 'viem';

const abi = [{
  type: 'function',
  name: 'fetchUint',
  inputs: [
    { name: 'url', type: 'string' },
    { name: 'selector', type: 'string' },
    { name: 'decimals', type: 'uint8' }
  ],
  outputs: [{ name: 'result', type: 'uint256' }]
}];

// Fetch Bitcoin price with 8 decimal places
const calldata = encodeFunctionData({
  abi,
  functionName: 'fetchUint',
  args: [
    'https://api.coingecko.com/api/v3/simple/price?ids=bitcoin&vs_currencies=usd',
    'bitcoin.usd',
    8
  ]
});

Fetch a string value

const abi = [{
  type: 'function',
  name: 'fetchString',
  inputs: [
    { name: 'url', type: 'string' },
    { name: 'selector', type: 'string' }
  ],
  outputs: [{ name: 'result', type: 'string' }]
}];

// Fetch a token symbol
const calldata = encodeFunctionData({
  abi,
  functionName: 'fetchString',
  args: [
    'https://api.example.com/token/info',
    'data.symbol'
  ]
});

Fetch a boolean value

const abi = [{
  type: 'function',
  name: 'fetchBool',
  inputs: [
    { name: 'url', type: 'string' },
    { name: 'selector', type: 'string' }
  ],
  outputs: [{ name: 'result', type: 'bool' }]
}];

// Check if a market is open
const calldata = encodeFunctionData({
  abi,
  functionName: 'fetchBool',
  args: [
    'https://api.example.com/market/status',
    'isOpen'
  ]
});

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