Logs & Events

Event logs are how smart contracts announce what happened — token transfers, swaps, votes, and ownership changes.

What Are Logs?

When a transaction executes, contracts can emit events. Each event is stored in the transaction receipt as a log entry containing:

  • Address — the contract that emitted it.
  • Topics — indexed fields, including the event signature hash, used for efficient filtering.
  • Data — the non-indexed payload of the event.

Logs are cheap for contracts to write and cheap for indexers to read — they are the backbone of how explorers, wallets, and analytics tools observe on-chain activity.

Decoding Events

A raw log looks like hashes and hex. OpenScan.AI decodes logs using contract ABIs so you see human-readable entries instead:

Transfer(from: 0x1234…, to: 0xabcd…, value: 1,500.00 eUSD)

instead of:

topics: [0xddf252ad…, 0x…1234, 0x…abcd]
data: 0x000000…5150…

Why Events Matter

  • Token tracking — every ERC-20/721/1155 balance change is a Transfer event; explorers build token histories entirely from logs.
  • dApp analytics — swaps, liquidity changes, and game actions are all recorded as events.
  • Alerting — monitoring tools subscribe to specific event signatures on specific contracts.

Finding Events in OpenScan.AI

  • The Logs tab on any transaction page lists every event the transaction emitted, decoded where the contract is verified.
  • Token and NFT pages aggregate Transfer events into clean transfer histories.
  • The REST API exposes log queries for developers building on indexed data.

Limitations

  • Events from unverified contracts can’t always be decoded — you’ll see the raw topics and data.
  • Logs record announcements, not state; a contract can emit misleading events. Cross-check against actual state changes when auditing.

Next Steps

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