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Encyclopedia Ethereum · Entry 111

Smart-contract events: logs, indexed fields and their limits

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Ethereum
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4 cited records
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Key facts

Key facts for Smart-contract events: logs, indexed fields and their limits
FactDetailSource
EmitterEach log identifies the address that emitted it.[1]
TopicsNon-anonymous ABI events usually place the event-signature hash in the first topic.[1]
ReversionLogs from reverted execution are discarded.[3]
01

Interpret topics and data with the correct ABI

Indexed parameters appear in topics, while non-indexed parameters are encoded in the data field. A dynamic indexed value such as a string is represented by a hash, so its original contents cannot simply be decoded from that topic.

The event declaration defines the interpretation. A generic list of hexadecimal words does not establish which fields represent an amount, token identifier or address.

02

Check the contract behind a Transfer label

Different contracts can emit events with the same signature. A malicious token can use a familiar Transfer event without being the genuine stablecoin contract a reader expected.

Check the chain and emitting address before interpreting a name or symbol. Then consider the contract’s actual code and balance accounting.

03

Keep a block reference with indexed events

RPC log queries return block and transaction context. Indexers need this context to follow the accepted chain and reconcile changed inclusions.

An event proves that particular code emitted particular data in the observed execution. Its business meaning depends on the contract and the wider transaction.

Direct answers

Questions people ask

Can every indexed event field be decoded back to its original value?

No. Dynamic indexed values can be represented by hashes. Their original contents require other information or a known candidate to compare.

Inspect the evidence

The answer and key facts have stable claim links. These records retain the scope and qualification when reused.

Ethereum contract events are logs emitted during execution. They record an emitting address, topics and data that an ABI can decode. Events help applications index activity, but a log’s name is not proof that its contents are truthful or that the emitter is the asset contract a reader intended to inspect.

Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.

Link to this claim
Emitter: Each log identifies the address that emitted it.

Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.

Link to this claim
Topics: Non-anonymous ABI events usually place the event-signature hash in the first topic.

Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.

Link to this claim
Reversion: Logs from reverted execution are discarded.

Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.

Link to this claim
Revision history
  1. — First publication after primary-source research and independent automated verification.

Source register

Sources and references

Retrieval dates and locators are recorded individually.
  1. Contract ABI SpecificationSolidity contributors

    ABI encoding, selectors, event topics and event data.

    Locator: Function Selector; Argument Encoding; Events; Errors; JSON · Version / scope: Solidity 0.8.30 documentation · Retrieved: 2026-10-02T17:03:42.824ZOpen source
  2. Ethereum JSON-RPCethereum.org contributors

    RPC response fields, transaction receipts, call simulation and log filtering.

    Locator: eth_getTransactionByHash; eth_getTransactionReceipt; eth_call; eth_getLogs; eth_getCode; eth_estimateGas; eth_getBalance; eth_getStorageAt; eth_getTransactionCount; default block parameter · Retrieved: 2026-10-02T17:03:42.060ZOpen source
  3. REVERT instructionEthereum Improvement Proposals

    State rollback and remaining gas behavior for a REVERT instruction.

    Locator: Specification · Version / scope: EIP/ERC-140; retrieved document hash recorded · Retrieved: 2026-10-02T17:03:42.150ZOpen source
  4. ERC-20 Token StandardEthereum Improvement Proposals

    Token supply, displayed units and balance accounting.

    Locator: totalSupply; balanceOf; transfer; decimals; approve; allowance; transferFrom; Transfer · Version / scope: ERC-20 · Retrieved: 2026-10-02T17:03:45.826ZOpen source
How this article was made

Research and drafting use AI assistance. A separate automated review checks claims against primary sources; no external expert or named human review is implied. Publication, substantive editing, source retrieval and verification are recorded separately. This version was independently checked by an automated reviewer on 2 October 2026.

Editorial method and corrections

Degrees of Satoshi editorial project. “Smart-contract events: logs, indexed fields and their limits.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/smart-contract-events/