Transaction simulation (eth_call + gas)

Dry-run a prospective transaction without broadcasting it: executes eth_call and eth_estimateGas against the latest block over the same keyless multi-endpoint public RPC pool as /api/evm-rpc (ethereum, base, polygon, arbitrum, optimism). Returns the return data and a gas estimate on success, or {success:false} with the revert reason when the call would fail. Strictly read-only — nothing is signed or broadcast.

Input

Example output

{
  "network": "base",
  "success": true,
  "returnData": "0x00000000000000000000000000000000000000000000000000000000000f4240",
  "gasEstimate": 31234,
  "revertReason": null
}

Try it — see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/tx-simulate \
  -H "Content-Type: application/json" \
  -d '{"network":"base","to":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","data":"0x70a08231000000000000000000000000abf4fabd7c416fb67202e5f9002389fc75e2a9d0"}'

The response is HTTP 402 Payment Required with exact payment requirements. Any x402 v2 client pays automatically and retries:

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/tx-simulate", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "network": "base",
    "to": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "data": "0x70a08231000000000000000000000000abf4fabd7c416fb67202e5f9002389fc75e2a9d0"
  }),
});

Part of these workflows

This tool is one step in a curated multi-tool workflow — agents can fetch the whole sequence as an MCP prompt or call https://agent402.tools/api/skill-packs/{slug}/prompt.

• Contract audit — Triage a smart contract before an agent interacts with it: verified source, heuristic vulnerability scan, known-address check, function-selector resolution, and a read-only dry-run of the exact call you plan to make.

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