onchain-decode-mcp

# FabTally Decode — MCP server

Developer on-chain **decoding** reads that turn raw EVM bytes into human-readable
JSON — the capability buried inside $49-999/mo RPC plans. Fronts the Decode HTTP
API at **https://decode.fabtally.com**. Holds no private key.

## Tools (all paid; a call with no payment returns the decoded x402 402 challenge)

| Tool | Price | What it does |
|------|-------|--------------|
| `decode_log` | $0.003 | **Flagship.** Decode event LOGS to JSON. `{chain, tx_hash}` decodes every log in a tx, or `{chain, address, topics[], data}` a single log; optional `abi`. Returns event name + canonical signature + named/typed args — handling tuple/array/nested params, anonymous events, indexed vs non-indexed. Resolves ABI via Sourcify/Blockscout + 4byte when none is given. |
| `decode_calldata` | $0.002 | Decode a function call. `{chain, to?, data, abi?}` → selector resolved to a function signature (provided ABI / verified source / 4byte.directory) + fully decoded typed arguments. |
| `selector_lookup` | $0.001 | Resolve a 4-byte function selector (`0x`+8 hex) or a 32-byte event topic (`0x`+64 hex) to human signature(s) via 4byte.directory + openchain.xyz, with a verified flag. |
| `abi_fetch` | $0.002 | Fetch a contract's verified ABI + metadata (Sourcify/Blockscout) + verification status + full proxy-implementation resolution (EIP-1967/1822/OZ-legacy/beacon) — returns the implementation ABI for proxies. Args: `address`, `chain`. |

Chains: **ethereum, base, arbitrum, optimism, polygon, bsc**.

Every tool also accepts an optional `x_payment` (base64 x402 payload) that is
forwarded as the `X-PAYMENT` header to settle the call and return the real result.
Humans can instead prepay by card and use an `X-FabTally-Key` credit key against
the HTTP API.

## Transports

- **stdio** (portable): `npx fabtally-decode-mcp` (bin: `fabtally-decode-mcp`)
- **streamable-http** (hosted): `https://decode.fabtally.com/mcp`

Config: `FABTALLY_DECODE_BASE` (default `https://decode.fabtally.com`).

Read-only, keyless, stateless, descriptive. Operated by Sunstone Soft
(fabtally.com). Not a security guarantee or financial advice.