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Gas Waiver enables gas-free transactions on Stable. With Gas Waiver, applications cover gas fees on behalf of users, so users can interact with contracts without holding USDT0 for gas. This guide covers integrating via the Waiver Server API. For the protocol-level specification (wrapper transaction mechanism, authorization, policy checks, execution semantics, security model), see Gas Waiver.

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Prerequisites

  • An API key for the Waiver Server, issued by the Stable team
  • Target contract address must be registered in the waiver’s AllowedTarget policy

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Waiver Server

Base URLs:
  • Mainnet: TBD
  • Testnet: https://waiver.testnet.stable.xyz
Authorization: Bearer <your-api-key>

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Overview

The integration flow has three steps:
  1. Build an InnerTx: the user signs a transaction with gasPrice = 0.
  2. Submit to Waiver Server: submit the signed transaction to the Waiver Server API.
  3. Handle the response: the waiver server wraps and broadcasts the transaction. Process the streamed results and surface the transaction hash to the user.

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Step 1: create the user’s InnerTx

The user signs a standard transaction with gasPrice = 0. The to address and method selector must be permitted by the waiver’s AllowedTarget policy. 
// config.ts
export const CONFIG = {
  RPC_URL: "https://rpc.testnet.stable.xyz",
  CHAIN_ID: 2201, // 988 for mainnet
  WAIVER_SERVER: "https://waiver.testnet.stable.xyz",
  USDT0_ADDRESS: "0x78Cf24370174180738C5B8E352B6D14c83a6c9A9",
};

import { ethers } from "ethers";
import { CONFIG } from "./config";

const provider = new ethers.JsonRpcProvider(CONFIG.RPC_URL);
const usdt0 = new ethers.Contract(CONFIG.USDT0_ADDRESS, [
  "function transfer(address to, uint256 amount) returns (bool)"
], provider);

const callData = usdt0.interface.encodeFunctionData("transfer", [
  recipientAddress,
  ethers.parseUnits("0.01", 18)
]);

const gasEstimate = await provider.estimateGas({
  from: userWallet.address,
  to: CONFIG.USDT0_ADDRESS,
  data: callData,
});

const nonce = await provider.getTransactionCount(userWallet.address);

const innerTx = {
  to: CONFIG.USDT0_ADDRESS,
  data: callData,
  value: 0,
  gasPrice: 0,
  gasLimit: gasEstimate,
  nonce: nonce,
  chainId: CONFIG.CHAIN_ID,
};

const signedInnerTx = await userWallet.signTransaction(innerTx);
gasPrice must be 0. If it is non-zero, the waiver server rejects the transaction.

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Step 2: submit to the Waiver Server

import { CONFIG } from "./config";

const API_KEY = process.env.WAIVER_API_KEY;

const response = await fetch(`${CONFIG.WAIVER_SERVER}/v1/submit`, {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "Authorization": `Bearer ${API_KEY}`,
  },
  body: JSON.stringify({
    transactions: [signedInnerTx],
  }),
});

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Batch submissions

You can submit multiple signed transactions in a single request: 
body: JSON.stringify({
  transactions: [signedTx1, signedTx2, signedTx3],
})
Each result line includes an index field corresponding to the transaction’s position in the array.

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Step 3: handle the response

The response is streamed as NDJSON (newline-delimited JSON). Each line corresponds to one submitted transaction. 
const reader = response.body.getReader();
const decoder = new TextDecoder();

while (true) {
  const { done, value } = await reader.read();
  if (done) break;

  const lines = decoder.decode(value).trim().split("\n");
  for (const line of lines) {
    const result = JSON.parse(line);
    if (result.success) {
      console.log(`tx ${result.index} confirmed: ${result.txHash}`);
    } else {
      console.error(`tx ${result.index} failed: ${result.error.message}`);
    }
  }
}
Success response: 
{"index": 0, "id": "abc123", "success": true, "txHash": "0x..."}
Failure response: 
{"index": 1, "id": "def456", "success": false, "error": {"code": "VALIDATION_FAILED", "message": "invalid signature"}}

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Error codes

CodeDescription
PARSE_ERRORFailed to parse transaction
INVALID_REQUESTMalformed request body
BATCH_SIZE_EXCEEDEDBatch size exceeds allowed maximum
VALIDATION_FAILEDTransaction validation failed (e.g., invalid signature, disallowed target)
BROADCAST_FAILEDFailed to broadcast to chain
RATE_LIMITEDRate limit exceeded
QUEUE_FULLServer queue at capacity
TIMEOUTRequest timed out

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API reference

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GET /v1/health

Health check endpoint. Authentication: none.

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POST /v1/submit

Submit a batch of signed inner transactions. Authentication: required (Bearer). Request body: 
{
  "transactions": ["0x<signedInnerTx1>", "0x<signedInnerTx2>"]
}
Response is streamed as NDJSON. Each line corresponds to a submitted transaction index.

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GET /v1/submit

WebSocket interface for streaming submissions. Authentication: required (Bearer).

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Key takeaways

  • Gas Waiver is a server-side integration: your backend submits signed user transactions to the Waiver Server. Users never interact with the Waiver Server directly.
  • The user always signs the InnerTx, preserving signature integrity. The waiver cannot modify the user’s transaction.
  • The target contract must be on the waiver’s AllowedTarget list.
See also:
Last modified on April 16, 2026