# Checkpoint402 Transaction Explainer

> Checkpoint402 Transaction Explainer is a paid API for AI agents from api.checkpoint402.com, paid per call via x402, $0.03/call, status unknown (last checked 2026-10-14).

Fetches a human-readable explanation of a blockchain transaction given its hash on Ethereum or Base

## Facts

- Endpoint: GET https://api.checkpoint402.com/v1/tx-explain?utm_source=zero.xyz
- Price: $0.03/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/checkpoint402-transaction-explainer-4ec74634
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_NWXxneb9_-_zsTgCbvtha

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 checkpoint402-transaction-explainer-4ec74634
```

Example prompt: Can you explain what this Ethereum transaction did: 0x4a7d3f2e1b9c8a56e0f1234abcd5678ef90abcd1234ef5678ab90cd1234ef5678?

## When to prefer this

Use this endpoint when you need a concise, human-readable explanation of a specific on-chain transaction by hash on Ethereum or Base. It is particularly well-suited for DeFi-related transactions where protocol context matters. Prefer it over generic block explorers when you need structured, agent-consumable output without managing API keys, and are comfortable with a per-call USDC micropayment.

## Known failure modes

- Invalid or malformed transaction hash returns an error
- Transaction hash not found on the specified chain returns not-found error
- Unsupported chain (neither 'base' nor 'ethereum') returns validation error
- Payment failure (insufficient USDC) results in HTTP 402 and no explanation returned
- Network timeout on slow block explorers may delay response

## How this service works

Explains any Base or Ethereum transaction in plain English: who sent what to whom, which tokens/NFTs moved, the function called, success/failure and fee — plus the structured decoded data.

## Output

A natural-language explanation of what the specified transaction did, including the action type (e.g. swap, transfer, liquidity provision), protocols involved, tokens and amounts, and any relevant DeFi or safety context.

## 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": [
      "hash"
     ],
     "properties": {
      "hash": {
       "type": "string",
       "description": "Transaction hash (0x + 64 hex chars)"
      },
      "chain": {
       "enum": [
        "base",
        "ethereum"
       ],
       "type": "string",
       "description": "Chain (default base)"
      }
     }
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/checkpoint402-transaction-explainer-4ec74634/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.checkpoint402.com](https://www.zero.xyz/host/api.checkpoint402.com/llms.txt)