Keccak-256 hash API: Ethereum function selectors and event topics

$0.01 per call · failed calls are never charged · no account or subscription: pay per call with a card key or USDC

Keccak-256 hash (the Ethereum hash) of text or of 0x hex bytes, as used for function selectors, event topics and storage slots. Use when building or decoding EVM calls.

When to use it

Build or decode EVM calls
Hash a function signature such as transfer(address,uint256) and get its 4-byte selector
Hash 0x hex bytes for event topics and storage slots

Run it free (25 free calls) Buy credits by card (from $1) Example result (JSON)

Inputs

Name	Type	Description
`text` (required)	string	Text, or 0x-prefixed hex bytes, up to 10,000 characters

Request

Over HTTP, with a card key from /credits:

curl -H "Authorization: Bearer adt_…" "https://tools.funwords.eu/keccak?text=transfer(address%2Cuint256)"

Or one of your 25 free calls, no key:

curl "https://tools.funwords.eu/keccak?text=transfer(address%2Cuint256)&trial=1"

Without a key, the same URL answers 402 Payment Required with x402 and MPP terms, so an agent with a wallet pays per call in USDC (Base, Polygon, Arbitrum or Solana over x402; Base or Tempo over MPP) and retries.

Example result

{
  "input": "transfer(address,uint256)",
  "inputType": "text",
  "keccak256": "0xa9059cbb2ab09eb219583f4a59a5d0623ade346d962bcd4e46b11da047c9049b",
  "selector": "0xa9059cbb"
}

From an AI agent (MCP)

Add the MCP server to Claude, Cursor or any MCP client. This tool is keccak, and the first 25 successful calls are free:

https://tools.funwords.eu/mcp

Questions

Text or bytes?

Both: plain text, or 0x-prefixed hex bytes, up to 10,000 characters.

How do I pay?

Each successful call costs $0.01; failed calls are not charged. The first 25 calls are free. Then pay with card credits (from $1; the key goes in an Authorization header or, for clients that can only fetch a URL, as api_key= in the URL) or per call in USDC over x402 or MPP. No account is needed.