signature-lookup

name	signature-lookup
description	Resolve EVM function selectors (4-byte) and event topic hashes to human-readable signatures. Queries openchain.xyz + 4byte.directory with a built-in fallback DB of 50+ common signatures. Batch mode, bytecode scanning, stdin pipe. Zero dependencies.

signature-lookup

Resolve EVM function selectors and event topic hashes to human-readable signatures. Zero deps.

When to use this skill

• You have a 4-byte selector like 0xa9059cbb and want to know it's transfer(address,uint256).
• You're reading event logs and need to identify topic0 hashes.
• You want to extract all function selectors from deployed bytecode.
• You need to quickly identify what a contract can do by scanning its bytecode.
• Pairs with calldata-decoder (decode full calldata) and event-decoder (decode full event logs).

What it does NOT require

• ethers.js / viem / web3.js
• npm install
• An API key
• A local node

Built-in DB covers 50+ of the most common ERC-20, ERC-721, Uniswap, and access-control signatures, so common lookups work even offline.

Script

lookup.mjs

# Single function selector
node lookup.mjs 0xa9059cbb

# Event topic hash
node lookup.mjs 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef

# Batch lookup
node lookup.mjs 0xa9059cbb 0x095ea7b3 0x23b872dd

# Extract and resolve selectors from bytecode
node lookup.mjs --scan 0x6080604052...

# Pipe from stdin
echo "0xa9059cbb 0x095ea7b3" | node lookup.mjs

Example output

[fn]    0xa9059cbb  transfer(address,uint256)  [builtin]
[fn]    0x095ea7b3  approve(address,uint256)  [builtin]
[event] 0xddf252ad...  Transfer(address,address,uint256)  [builtin]

3/3 resolved.

Sources

1. Built-in DB — instant, no network. Covers ERC-20, ERC-721, Uniswap v2/v3, OpenZeppelin access control, and common DeFi signatures.
2. openchain.xyz — large public signature database (same one Etherscan uses).
3. 4byte.directory — community-maintained Ethereum signature registry.

Both APIs are queried in parallel; results are deduplicated.