Base Transaction Decoder MCP server

base-transaction-decoder

One MCP tool: explaintransaction(txhash) → strict JSON explanation of any Base mainnet transaction.

Feed it a transaction hash. Get back what happened, in plain English, plus the structured facts: what moved, who was involved, what to be careful about, what it cost. Deterministic onchain decode — no LLM anywhere in the response path, so the same input always produces the same output, there is nothing to hallucinate, and the JSON contract is stable enough to parse blind.

Base mainnet (chain id 8453) only.

Links: Live endpoint · Docs · OpenAPI · MCP registry: io.github.0200project/base-transaction-decoder · Site

Formerly base-tx-explain. The tool, the endpoint and the schema are unchanged — only the name moved, so that a search for "transaction" or "decoder" can find it. The repository keeps its original name, so existing clones, forks and links still work.

For agents

// tools/call → explain_transaction
{ "tx_hash": "0x0c84b951051f779903b57af9225ca570c77cd5531195968dd78106a69d6c4d8c" }

returns (as both structuredContent and stringified JSON in content[0].text):

{
  "summary": "0x401d...f2c5 swapped 0.03 ETH for 12,899,422 WNL via Uniswap V4 PoolManager.",
  "action_type": "swap",
  "status": "success",
  "assets_moved": [
    { "token": "ETH", "amount": "0.03", "from": "0x401d...", "to": "0xd0a4...", "token_address": null, "standard": "native" },
    { "token": "WNL", "amount": "12899422.144134853458613801", "from": "0x4985...", "to": "0x401d...", "token_address": "0xb200...9a01", "standard": "erc20" }
  ],
  "counterparties": [
    { "address": "0xd0a4...", "label": null },
    { "address": "0x4985...", "label": "Uniswap V4 PoolManager" }
  ],
  "risk_flags": [
    { "flag": "unverified_contract", "detail": "The target contract 0xd0a4...e4bf has no verified source code on Sourcify." }
  ],
  "checks": {
    "contract_verification": "ok",
    "first_interaction": "ok",
    "drainer_blacklist": "ok",
    "unchecked_addresses": [],
    "note": null
  },
  "gas_paid_usd": 0.020562,
  "timestamp": "2026-08-20T03:54:19.000Z",
  "block_number": 50204356,
  "tx_hash": "0x0c84...4c8c",
  "basescan_url": "https://basescan.org/tx/0x0c84...4c8c",
  "partial": false
}

Field contract

Shortened. The full README is on GitHub.