Encyclopedia Ethereum · Entry 107
Ethereum address checksums: what mixed-case letters can detect
In this article
At a glance
Key facts
| Fact | Detail | Source |
|---|---|---|
| Bytes | Changing letter case does not change the underlying hexadecimal address value. | [1] |
| Checksum | Capitalization is derived from a hash of the lowercase address text. | [1] |
| Limits | The checksum detects errors probabilistically; it is not identity verification. | [1] |
A readable error check in the same address length
Hexadecimal letters can be printed in upper or lower case. EIP-55 uses that choice to encode checksum information, while digits carry no case distinction.
A receiving interface can recalculate the expected capitalization and flag a mismatch. Not every interface requires mixed-case input, so acceptance alone does not demonstrate that a checksum was checked.
Valid encoding can still point to an attacker
Someone else’s address can have a perfectly valid checksum. A checksum is designed to detect accidental corruption of an identifier, not decide whether the destination belongs to the person you intended.
Compare the complete trusted destination and network context. Matching only a few leading or trailing characters provides much less information than checking the full address.
Keep network identity separate
The EIP-55 algorithm does not use a chain ID. The same checksummed address can therefore be displayed on different compatible networks.
For tokens, verify both the asset’s contract and the recipient on the intended chain. Address formatting cannot repair a transfer sent to an unsupported network.
Direct answers
Questions people ask
Is a lowercase Ethereum address always invalid?
No. Lowercase text can represent valid address bytes, and some correct EIP-55 outputs are entirely lowercase. A wallet accepting lowercase input does not by itself show that it checked the expected checksum capitalization.
Inspect the evidence
The answer and key facts have stable claim links. These records retain the scope and qualification when reused.
EIP-55 encodes a checksum in the capitalization of an Ethereum address’s hexadecimal letters. Correct checking can detect many typing mistakes without changing the underlying address bytes. It does not prove the recipient’s identity, select a network or guarantee that every possible error will be caught.
Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.
Link to this claimBytes: Changing letter case does not change the underlying hexadecimal address value.
Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.
Link to this claimChecksum: Capitalization is derived from a hash of the lowercase address text.
Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.
Link to this claimLimits: The checksum detects errors probabilistically; it is not identity verification.
Scope: Ethereum · data through 2026-10-02. Verification: verified · 2026-10-02T18:12:41.505Z.
Link to this claimRevision history
- — First publication after primary-source research and independent automated verification.
Source register
Sources and references
Retrieval dates and locators are recorded individually.- Mixed-case checksum address encodingEthereum Improvement Proposals
Capitalization encodes a checksum without changing the address bytes.
Locator: Specification; Rationale; Test Cases · Version / scope: EIP/ERC-55; retrieved document hash recorded · Retrieved: 2026-10-02T17:03:42.205ZOpen source - Ethereum accountsethereum.org contributors
Key-controlled and code-controlled accounts, balances, nonces and storage.
Locator: Account types; An account examined; Account creation · Retrieved: 2026-10-02T17:03:41.958ZOpen source - Simple replay attack protectionEthereum Improvement Proposals
Transaction chain ID domain separation; not blanket protection for all signatures.
Locator: Specification · Version / scope: EIP/ERC-155; retrieved document hash recorded · Retrieved: 2026-10-02T17:03:42.312ZOpen source
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 correctionsDegrees of Satoshi editorial project. “Ethereum address checksums: what mixed-case letters can detect.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/ethereum-address-checksums/