Ethereum Address Checksum (EIP-55) — Free & Private

A free edge API by formatho.com, privacy-first developer tools.

Free, no signup, runs entirely in your browser — your data never leaves your device.

🔓 Free🔒 Zero tracking🚫 No data collection⚡ Edge-fast

Usage

curl "https://address-checksum-formatho.filesformatho.workers.dev/api?address=0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed"
# → { "address": "0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed", "checksum_valid": false, ... }

curl "https://address-checksum-formatho.filesformatho.workers.dev/api?address=0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359"
# → { "address": "0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359", "checksum_valid": true }

Pass any 40-hex-character address (optional 0x prefix). GET or POST JSON — {"address": "0x…"}. Returns the EIP-55 checksummed form, per-position case mismatches, and an all-lower/all-upper advisory.

Why it matters: EIP-55 encodes a keccak-256 checksum in the letter casing of an address, so a single mistyped character is caught before funds leave your wallet.

Full parameter reference: /api endpoint.

Privacy-first: checksumming happens in-memory at the edge and your input is never logged or stored.

Full browser tool

Checksum addresses entirely client-side: EIP-55 Address Checksum on formatho.com.

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