# ExactGate x402 Preflight Validator

> ExactGate x402 Preflight Validator is a paid API for AI agents from exactgate-x402.insertnameheree.chatgpt.site, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-14).

Simulates a Base blockchain transaction to estimate gas and determine safety before submission, paid per call via x402 USDC micropayment.

## Facts

- Endpoint: POST https://exactgate-x402.insertnameheree.chatgpt.site/v1/base/preflight
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/exactgate-x402-preflight-validator-049b0559
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_HJb20nS25hYk_MZkyZLBP

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 exactgate-x402-preflight-validator-049b0559 -d '<json body>'
```

Example prompt: Before I send this contract call, can you simulate the transaction on Base mainnet — from address 0xAbCd1234...5678, to contract 0xDead5678...AbCd, with calldata 0xa9059cbb000000...0064 and value 0x0 — and tell me the gas estimate and whether it's safe to submit?

## When to prefer this

Choose this endpoint when you need a deterministic, no-side-effect dry-run of a Base L2 transaction before committing gas. It is ideal for agent workflows that must validate smart contract interactions, estimate costs, or catch reverts programmatically without risking real funds. Prefer it over generic RPC eth_call wrappers when you want a structured JSON safety verdict (safeToSubmit) rather than raw RPC output, and when you are comfortable paying $0.02 USDC per simulation via x402 micropayment.

## Known failure modes

- Invalid Ethereum address format for 'to' or 'from' returns a 400 validation error
- Malformed or odd-length hex calldata in 'data' is rejected by pattern validation
- Calldata exceeding 8194 hex characters (4097 bytes) is rejected
- Payment failure via x402 protocol results in 402 Payment Required before simulation runs
- Simulated call reverts on-chain returns safeToSubmit: false with revert data in callResult
- Network issues reaching Base RPC may return 503 or timeout errors

## How this service works

Deterministic Base receipt and transaction preflight APIs, paid per call with x402 USDC.

## Output

Returns a JSON object with: chainId (8453 for Base), a boolean 'contract' indicating if the target is a contract, 'callResult' (raw hex return data), 'gasEstimate' (estimated gas units as a string), 'safeToSubmit' (boolean safety verdict), and a 'note' confirming no transaction was signed or broadcast.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "to": {
   "type": "string",
   "pattern": "^0x[0-9a-fA-F]{40}$"
  },
  "data": {
   "type": "string",
   "pattern": "^0x(?:[0-9a-fA-F]{2})*$",
   "maxLength": 8194
  },
  "from": {
   "type": "string",
   "pattern": "^0x[0-9a-fA-F]{40}$"
  },
  "value": {
   "type": "string",
   "pattern": "^0x[0-9a-fA-F]+$"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "note": "Simulation only; no transaction was signed or broadcast.",
  "chainId": 8453,
  "contract": true,
  "callResult": "0x",
  "gasEstimate": "48231",
  "safeToSubmit": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/exactgate-x402-preflight-validator-049b0559/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from exactgate-x402.insertnameheree.chatgpt.site](https://www.zero.xyz/host/exactgate-x402.insertnameheree.chatgpt.site/llms.txt)