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/ Event Topic Calculator

Event Signature

Event Topic (Topic0 - 32 bytes)

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Event Topic Calculator

Calculate event signature hashes for Solidity events

■ 01

What are Event Topics?

In Ethereum, events are stored in transaction logs. The first topic (topic0) is always the keccak256 hash of the event signature. This is used to filter and identify specific events.

■ 02

How does it work?

Event Signature Format Event signatures follow the format: EventName(type1,type2,...). Note that parameter names are omitted, only types are included. For example: Transfer(address,address,uint256)

■ 03

Sample Cases

Covers ERC-20 Transfer event, ERC-20 Approval event, and ERC-721 Transfer event so you can compare common inputs and outputs quickly.

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/ Integration

Source code from the selected tool, shown here alongside the live version on the right.

/ Source Code

TypeScript

typescript

// npm install viem

import { keccak256, toBytes, toEventSignature } from 'viem';

// Calculate event topic (Topic0) from event signature
function getEventTopic(eventSignature: string): string {
  // Hash the event signature with keccak256
  const topic = keccak256(toBytes(eventSignature));
  return topic;
}