Best Free Online Developer Tools to Use in 2026
A practical, opinionated list of the best free online developer tools worth using in 2026, organized by category so you can find what you need fast.
Aug 08, 2026
Ethereum Address Validator
Validate Ethereum addresses with EIP-55 checksum verification, detect address format, and suggest correct checksummed address.
Address Validator
Enter an Ethereum address (0x + 40 hex characters) to validate with EIP-55 checksum verification.
Checksum (EIP-55)
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Format
-
Length
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- Enter an Ethereum address — Type or paste an Ethereum address (starts with 0x followed by 40 hex characters).
- Automatic validation — The address is validated in real-time. The tool checks format, hex characters, and EIP-55 checksum for mixed-case addresses.
- View address details — See the checksum status, address format type, and character length.
- Try examples — Click the Example button to test with valid Ethereum addresses.
All validation is performed 100% client-side in your browser. No address data is sent to any server.
What Is EIP-55?
EIP-55 (Ethereum Improvement Proposal 55) defines a method for adding checksum information to Ethereum addresses by using mixed-case characters. Since Ethereum addresses are case-insensitive hex strings, EIP-55 encodes a checksum in the capitalization of the letters (a-f) to help detect typing errors.
The checksum works by taking the Keccak-256 hash of the lowercase address (without 0x prefix). If the nth hex digit of the hash is 8 or higher (bit 3 set), the corresponding character in the address is capitalized. This creates a human-readable checksum that is backward-compatible with all existing Ethereum software.
Addresses in all-lowercase or all-uppercase are still technically valid, but they lack the error-detection benefits of the EIP-55 checksum. Most Ethereum wallets now display addresses in EIP-55 mixed-case format.
Ethereum Address Format
| Property | Value |
|---|---|
| Prefix | 0x |
| Total Length | 42 characters (0x + 40 hex) |
| Character Set | 0-9, a-f, A-F |
| Checksum Standard | EIP-55 (Keccak-256 based) |
| Case Sensitivity | Case-insensitive, but mixed-case has checksum |
What is an Ethereum address?
An Ethereum address is a 42-character hex string starting with 0x. It represents the last 20 bytes of the Keccak-256 hash of the public key, with EIP-55 optional mixed-case checksum encoding.
What is EIP-55 checksum?
EIP-55 adds error-detection to Ethereum addresses by capitalizing certain letters based on the Keccak-256 hash of the address. This helps detect typing errors and prevents sending funds to incorrect addresses.
Are lowercase/uppercase addresses valid?
Yes. All-lowercase and all-uppercase Ethereum addresses are technically valid, but they do not carry the EIP-55 checksum. It is recommended to use the mixed-case checksummed format for safety.
Does a valid address mean the address has ETH?
No. A valid address only confirms the address is correctly formatted with a valid checksum. It does not indicate ownership, activity, or balance. Use a blockchain explorer to check balances.
What is the difference between EIP-55 and Base58Check?
Bitcoin uses Base58Check which adds explicit checksum bytes to the address. Ethereum uses EIP-55 which encodes the checksum in the letter casing of existing hex characters, making it backward-compatible with systems that ignore case.
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