TxRelay API

Introduction

TxRelay API allows you to build and broadcast blockchain transactions without sharing your private keys. We handle:

• Gas estimation
• Nonce management
• Transaction broadcasting
• Status monitoring & webhooks

How it works:

1. You call /prepare → We return an unsigned transaction.
2. You sign it locally with your private key.
3. You call /broadcast → We send it to the blockchain.

Official SDK

The easiest way to use TxRelay. Full TypeScript support with autocomplete.

npm install txrelay-sdk

import { TxRelay } from 'txrelay-sdk';

const client = new TxRelay('YOUR_API_KEY');

// Prepare a transaction
const { unsignedTx } = await client.prepareTransaction({
  from: '0xYourWallet...',
  to: '0xRecipient...',
  amount: '0.1',
  chain: 'ethereum'
});

// Sign locally with ethers.js
const signedTx = await wallet.signTransaction(unsignedTx);

// Broadcast
const { txHash } = await client.broadcastTransaction({
  signedTx,
  chain: 'ethereum'
});

// Check balance
const { balance } = await client.getBalance('0x...', 'ethereum');

// Account info
const account = await client.getAccount();

Authentication

All API requests require an API key in the header:

x-api-key: YOUR_API_KEY

Get your API key from the Dashboard.

Supported Chains

API Endpoints

Base URL: https://api.txrelay-api.com/api/v1

Transactions

// Request
{
  "from": "0xYourWallet...",
  "to": "0xRecipient...",
  "amount": "0.1",
  "chain": "ethereum"
}

// Response
{
  "unsignedTx": { ... },
  "metadata": {
    "estimatedFee": "0.0001",
    "totalCost": "0.1001"
  }
}

// Request
{
  "from": "0xYourWallet...",
  "to": "0xRecipient...",
  "amount": "100",
  "tokenAddress": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
  "chain": "ethereum"
}

// Request
{
  "signedTx": "0x02f8...",
  "chain": "ethereum"
}

// Response
{
  "txHash": "0x...",
  "status": "queued"
}

Balance & Account

Webhooks

Receive real-time notifications when transactions are confirmed.

Webhook Payload

{
  "id": "evt_...",
  "event": "transaction.confirmed",
  "created_at": 1702000000,
  "data": {
    "txHash": "0x...",
    "status": "confirmed",
    "blockNumber": 12345678
  }
}

Verifying Signatures

We sign every webhook with your secret. Header: X-TxRelay-Signature

// Node.js
const crypto = require('crypto');
const [tPart, sigPart] = signature.split(',');
const timestamp = tPart.split('=')[1];
const sig = sigPart.split('=')[1];

const expected = crypto
  .createHmac('sha256', YOUR_WEBHOOK_SECRET)
  .update(`${timestamp}.${JSON.stringify(body)}`)
  .digest('hex');

if (sig === expected) { /* Verified */ }

Error Codes

All errors return:

{
  "success": false,
  "error": "ValidationError",
  "message": "Invalid wallet address"
}

Rate Limits & Pricing

Rate limit headers are included in every response:

X-RateLimit-Limit: 30
X-RateLimit-Remaining: 25
X-RateLimit-Reset: 2025-12-08T01:00:00Z
X-Monthly-Limit: 100
X-Monthly-Used: 42