ToolVet
75trust / 100

Simulate Transaction

by Transaction Preflight in Onchain & crypto

x402 APIPassing, checked 16 min ago

Simulates an unsigned Base or Base Sepolia EVM transaction with read-only RPC calls before an agent signs or broadcasts it. Returns execution/revert status, gas estimate, decoded top-level ERC-20 transfers and approvals, unlimited-approval warnings, and a risk signal. It never signs, holds keys, or broadcasts. Standard RPC does not expose complete internal/token state diffs.

POST https://mcp.dropenginehq.com/api/simulate-transaction

Last 30 days

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Status and outage history · Atom feed

Uptime
100%
Response time
513 ms typical, 611 ms slowest 5%
Last check
16 min ago
Next check
in 16 min

How to call it

POST https://mcp.dropenginehq.com/api/simulate-transaction

Each call costs $0.02 in USDC on Base, paid with the request over x402.

Run a free test callOne unpaid request, the way an agent sends it. You see the payment challenge it gets back. Nothing is charged.

Example request

From the listing.

POST https://mcp.dropenginehq.com/api/simulate-transaction
content-type: application/json

{
  "chain": "base",
  "data": "0x",
  "from": "0x1111111111111111111111111111111111111111",
  "to": "0x1111111111111111111111111111111111111111",
  "value": "0"
}

Parameters

ParameterTypeRequiredDescription
chainstringYesBase mainnet, or Base Sepolia for test transactions. One of: base, base-sepolia.
datastringYesUnsigned transaction calldata; no signing material.
fromstringYes
tostringYes
valuestringYesNative value in wei, as an integer string.

Example response

The listing has no example response.

Call it from code

The curl command shows the payment challenge. The JavaScript and Python versions pay and call, and never pay more than $0.02.

curl: see the payment challenge
# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://mcp.dropenginehq.com/api/simulate-transaction' \
  -H 'content-type: application/json' \
  --data-raw '{"chain":"base","data":"0x","from":"0x1111111111111111111111111111111111111111","to":"0x1111111111111111111111111111111111111111","value":"0"}'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - -X POST 'https://mcp.dropenginehq.com/api/simulate-transaction' \
  -H 'content-type: application/json' \
  --data-raw '{"chain":"base","data":"0x","from":"0x1111111111111111111111111111111111111111","to":"0x1111111111111111111111111111111111111111","value":"0"}' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode
JavaScript: pay and call
// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fmcp.dropenginehq.com%2Fapi%2Fsimulate-transaction&method=POST
const res = await pay("https://mcp.dropenginehq.com/api/simulate-transaction", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "chain": "base",
    "data": "0x",
    "from": "0x1111111111111111111111111111111111111111",
    "to": "0x1111111111111111111111111111111111111111",
    "value": "0"
  }),
});
console.log(res.status, await res.text());
Python: pay and call
# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://mcp.dropenginehq.com/api/simulate-transaction",
        json={
            "chain": "base",
            "data": "0x",
            "from": "0x1111111111111111111111111111111111111111",
            "to": "0x1111111111111111111111111111111111111111",
            "value": "0",
        },
    )
    print(res.status_code, res.text)

Security scan

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Recent checks

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