Address Codec
Paste any crypto address and this tool identifies its format and verifies its checksum locally: Bitcoin legacy Base58Check (P2PKH / P2SH), Bech32 and Bech32m segwit addresses (P2WPKH, P2WSH, taproot P2TR — witness version and program decoded), and Ethereum's EIP-55 mixed-case checksum, recomputed from keccak-256.
This tool is plain client-side JavaScript — no accounts, no server calls, no telemetry, not even a web font from a CDN. To keep it forever: press Ctrl + S (Mac: Cmd + S), choose "Webpage, Complete", and open the saved file any time — with Wi-Fi off, in airplane mode, on a machine that never touches the internet.
Analyze an address
Paste any crypto address and this tool identifies its format and verifies its checksum locally: Bitcoin legacy Base58Check (P2PKH / P2SH, with checksum validation), Bech32 and Bech32m segwit addresses (P2WPKH, P2WSH, taproot P2TR — witness version and program decoded), and Ethereum's EIP-55 mixed-case checksum, recomputed from keccak-256. It also warns you when you paste something that should never touch a website, like a WIF private key.
How the Address Codec works
Every mainstream blockchain address is a wrapper around a hash of a public key or a script, and each wrapper has its own encoding and its own error-detection mechanism. The codec identifies which wrapper you are looking at by prefix and alphabet first: 1 and 3 addresses are Base58Check, bc1 addresses are bech32 or bech32m depending on the witness version, and 0x addresses are Ethereum's hexadecimal with EIP-55 capitalization.
Verification then goes deeper than pattern-matching. For Base58Check the tool decodes the string, recomputes double-SHA-256 over the payload, and compares the four-byte checksum — this catches typos that would otherwise silently redirect funds to a nonexistent address. For segwit addresses it validates the bech32 (version 0) or bech32m (version 1+) checksum, decodes the witness program, and tells you whether the length is legal for P2WPKH, P2WSH or taproot. For Ethereum it recomputes the keccak-256 hash of the lowercase address and checks whether the upper/lowercase pattern matches — the EIP-55 checksum lives in the capitalization itself.
The tool also looks out for you in the other direction: if you paste something that decodes as a WIF private key (a 5, K or L string with a valid checksum), it stops and warns you instead of analyzing it, because a private key pasted into any website is a key that should be considered burned. Everything here runs locally — this page cannot check balances, history, or whether an address "exists" on chain, and that is by design: a codec that stays offline can never leak the addresses you are inspecting.
Address Codec — questions
What does a valid checksum actually mean? +
It means the address was typed or copied correctly — the checksum embedded in the encoding matches what the tool recomputes. It says nothing about who controls the address or whether it has funds. A checksum-valid address that differs from the one your counterparty gave you is still the wrong address.
Why did it warn me when I pasted a 5/K/L string? +
Strings starting with 5, K or L that pass Base58Check are almost always WIF private keys — the actual secret that controls funds, not an address. The tool refuses to analyze them and tells you to treat the key as exposed if it was ever pasted anywhere untrusted.
Can it check an address balance or history? +
No — and that is deliberate. Balance queries require contacting a blockchain API, which would associate the address you are checking with this tool's requests. The codec is a purely local format-and-checksum inspector; use a block explorer you trust for on-chain data.
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