# Base Transaction Calldata Preflight Inspector

> Base Transaction Calldata Preflight Inspector is a paid API for AI agents from base-agent-preflight.bytoken2023.workers.dev, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-15).

Decodes and analyzes EVM calldata for a Base transaction before signing, flagging token transfers, approvals, unlimited spending allowances, and unknown function selectors.

## Facts

- Endpoint: GET https://base-agent-preflight.bytoken2023.workers.dev/v1/x402/base/transaction-intent
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/base-transaction-calldata-preflight-inspector-4c5ff26a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_oKM33oHaCWs9JouRRRhhc

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 base-transaction-calldata-preflight-inspector-4c5ff26a
```

Example prompt: Before I sign this Base transaction to contract 0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48 with calldata 0x095ea7b3000000000000000000000000deadbeefdeadbeefdeadbeefdeadbeefdeadbeef ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff and no ETH value, can you decode what it actually does and flag if it's an unlimited token approval?

## When to prefer this

Use this endpoint when an AI agent is about to sign or broadcast a Base network transaction and needs to understand what the calldata actually does before committing — especially for DeFi interactions involving token approvals, transfers, or unfamiliar contract calls. Prefer over generic ABI decoders when you need a risk-oriented assessment with unlimited-approval and unknown-selector flags specific to the Base chain.

## Known failure modes

- Invalid 'to' address format (not a 40-char hex) returns validation error
- Malformed or truncated calldata returns decoding failure
- Unknown function selector returns flagged unknown-selector warning rather than full decode
- Missing required 'to' or 'data' query params returns 400-level error
- Payment not included or insufficient USDC triggers x402 payment required response

## How this service works

Machine-payable service intelligence for discovering, verifying, and monitoring identity, risk, authorization, execution-preflight, and evidence APIs before autonomous agents spend.

## Output

Returns a structured assessment including the decoded activity (e.g. ERC-20 approve, transfer), identity information about the contract, a risk assessment flagging unlimited approvals or unknown selectors, and provenance metadata — all machine-readable so the agent can decide whether to proceed with signing.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "to",
      "data"
     ],
     "properties": {
      "to": {
       "type": "string",
       "pattern": "^0x[a-fA-F0-9]{40}$",
       "description": "Base destination contract or account."
      },
      "data": {
       "type": "string",
       "pattern": "^0x(?:[a-fA-F0-9]{2})*$",
       "maxLength": 8194,
       "description": "Hex-encoded EVM calldata."
      },
      "value": {
       "type": "string",
       "pattern": "^[0-9]+$",
       "description": "Native ETH value in wei. Defaults to zero."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "network": {
       "type": "string"
      },
      "product": {
       "type": "string"
      },
      "activity": {
       "type": "object"
      },
      "identity": {
       "type": "object"
      },
      "assessment": {
       "type": "object"
      },
      "provenance": {
       "type": "object"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "network": "eip155:8453",
  "product": "evm-transaction-intent",
  "assessment": {
   "flags": [],
   "risk_level": "low",
   "risk_score": 0
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/base-transaction-calldata-preflight-inspector-4c5ff26a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from base-agent-preflight.bytoken2023.workers.dev](https://www.zero.xyz/host/base-agent-preflight.bytoken2023.workers.dev/llms.txt)