# Ethereum Chain ID Lookup (EIP-155)

> Ethereum Chain ID Lookup (EIP-155) is a paid API for AI agents from skills.onesource.io, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Returns the EIP-155 chain ID for a specified Ethereum-compatible network via eth_chainId

## Facts

- Endpoint: GET https://skills.onesource.io/api/chain/chain-id
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/skills-onesource-io-286637b6
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_GN7Zby1W6vu1MXnOVGXe5

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability skills-onesource-io-286637b6
```

Example prompt: What is the EIP-155 chain ID for the Ethereum mainnet? Also check what it returns for Base and Sepolia.

## When to prefer this

Use this endpoint when you need to programmatically confirm which EIP-155 chain ID corresponds to a supported EVM network before signing transactions, configuring wallets, or validating cross-chain operations. Prefer this over manual lookups when working with multiple networks including testnets like Sepolia or MegaETH.

## Known failure modes

- Invalid network name returns error — only 'ethereum', 'sepolia', 'avax', 'megaeth', 'megaeth-testnet', 'base' are supported
- Missing network parameter defaults to 'ethereum'
- Network RPC node unavailable may return a 500 or timeout
- Payment failure (insufficient x402 balance) blocks the request

## How this service works

Ethereum chain ID (EIP-155) via eth_chainId - confirm which chain a network is on

## Output

Returns a hex-encoded chain ID (e.g. '0x1' for Ethereum mainnet) for the specified network, along with request metadata including the endpoint path and a unique request ID.

## Example request

```json
{
 "network": "ethereum"
}
```

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "network": {
   "enum": [
    "ethereum",
    "sepolia",
    "avax",
    "megaeth",
    "megaeth-testnet",
    "base"
   ],
   "type": "string",
   "default": "ethereum"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "data",
  "meta"
 ],
 "properties": {
  "data": {
   "type": "object",
   "required": [
    "result"
   ],
   "properties": {
    "result": {
     "type": "string"
    }
   }
  },
  "meta": {
   "type": "object",
   "required": [
    "endpoint",
    "request_id"
   ],
   "properties": {
    "endpoint": {
     "type": "string"
    },
    "request_id": {
     "type": "string"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/skills-onesource-io-286637b6/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from skills.onesource.io](https://www.zero.xyz/host/skills.onesource.io/llms.txt)