# Vextorium EVM Transaction Builder

> Vextorium EVM Transaction Builder is a paid API for AI agents from api.vextorium.com, paid per call via x402, $0.004/call, status unknown (last checked 2026-10-29).

Builds an unsigned EVM transaction payload (native transfer, ERC-20 transfer, or ERC-20 approve) with full EIP-1559 fee estimates, gas, nonce, and chain ID — ready to sign.

## Facts

- Endpoint: POST https://api.vextorium.com/construir-transaccion-pago?utm_source=zero.xyz
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/vextorium-evm-transaction-builder-8e8ca328
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mcPuyMlDtHTCPUVqxQBV_

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 vextorium-evm-transaction-builder-8e8ca328 -d '<json body>'
```

Example prompt: Build me an unsigned EVM transaction to transfer 50 USDC from 0xABC...123 to 0xDEF...456 on Base — include the current EIP-1559 fees and gas estimate so I can sign and send it myself.

## When to prefer this

Choose this endpoint when you need to construct an EVM transaction for signing externally — ideal for wallets, signing services, or agents that manage their own private keys and need accurate EIP-1559 fee data baked in. Prefer this over on-chain submission services when you want to inspect, modify, or batch-sign transactions before broadcasting. Best suited for native transfers and ERC-20 transfers/approvals on supported EVM chains without needing to implement RPC calls yourself.

## Known failure modes

- Invalid or missing wallet address (desde/para) returns validation error
- Unsupported network identifier returns error indicating chain not found
- Zero or negative amount fails input validation
- Token address missing for transferencia_token or aprobar_token actions
- RPC timeout on target chain causes gas estimation failure
- Token contract not found on specified network

## How this service works

Build an EVM transaction ready to sign (never signed or sent): native transfer, ERC-20 transfer or ERC-20 approve, with to, data, value, nonce, chainId, estimated gas and current EIP-1559 fees, plus a simulation that warns if it would revert and the estimated cost.

## Output

Returns a fully formed unsigned transaction object containing: to, from, data (calldata), value (in hex), nonce, chainId, type, maxFeePerGas, maxPriorityFeePerGas, and gas (all hex-encoded), along with estimated gas units, estimated cost in USD, estimated cost in native token, token info (address, decimals), action type, network identifier, and an optional simulation note.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "red": {
   "type": "string"
  },
  "para": {
   "type": "string"
  },
  "desde": {
   "type": "string"
  },
  "token": {
   "type": "string"
  },
  "accion": {
   "enum": [
    "transferencia_nativa",
    "transferencia_token",
    "aprobar_token"
   ],
   "type": "string"
  },
  "cantidad": {
   "type": "number"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/vextorium-evm-transaction-builder-8e8ca328/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.vextorium.com](https://www.zero.xyz/host/api.vextorium.com/llms.txt)