Base58Check encoder & decoder

Base58Check is the Bitcoin binary-to-text format that wraps a payload with a four-byte checksum derived from double SHA-256, then encodes the whole sequence with the Bitcoin Base58 alphabet. This Base58Check encoder accepts a hex or UTF-8 payload and returns a Base58Check string; the decoder reverses the map, recomputes SHA256(SHA256(payload)), and reports a clear invalid_input error when the stored checksum does not match.

What Base58Check adds on top of Base58

Base58Check closes that gap. Four checksum bytes give roughly one in four billion chance of an undetected single-character typo in practice, which is why Bitcoin P2PKH addresses, many extended keys, and related tools standardize on this construction. This landing targets people searching for a Base58Check encoder, Base58Check decoder, or Bitcoin checksum converter online; it is not plain Base58 without a checksum, not Base64, and not a full address-type classifier that interprets version bytes for every network. Plain Base58 maps bytes to fifty-eight unambiguous characters by treating the payload as a big-endian integer and repeatedly dividing by fifty-eight, using the Bitcoin alphabet that drops zero, capital O, capital I, and lowercase L. That encoding alone is human-friendly but has no integrity protection: one mistyped glyph becomes another valid string that decodes to different bytes. Before encoding, the encoder computes SHA-256 of the payload, then SHA-256 of that digest, and appends the first four bytes of the outer hash as a checksum. The combined buffer—original payload plus those four bytes—is then Base58-encoded exactly like raw Base58, including the leading-zero to leading-one convention. On decode, the process runs in reverse: Base58 decode yields bytes; the last four are the claimed checksum; double SHA-256 of the remaining payload must equal those four bytes or the operation fails.

How to call the API and what the response contains

With format utf8, text is encoded as UTF-8 bytes before checksumming. Send a JSON body with a required string field text (aliases input, value, data, and payload), an optional mode of encode or decode (default encode), and an optional format of hex or utf8 (default hex). Whitespace inside hex is stripped; odd length or non-hex digits return invalid_input. Decode mode treats text as a Base58Check string under the Bitcoin alphabet, verifies the double-SHA256 checksum, and returns the payload as lowercase hex when format is hex, or as a UTF-8 string when format is utf8 (binary payloads that are not valid UTF-8 must use hex). On successful encode the response includes mode, format, input, result and base58check with the same encoded string, payload_hex, checksum_hex, the alphabet constant and alphabet_name bitcoin, payload_bytes, output_length, and a short English message. On successful decode you also get checksum_valid set to true, input_length, and a message confirming verification. Failed validation—missing text, bad hex, unknown mode or format, invalid Base58 characters, payloads too short to hold a checksum, or checksum mismatch—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item.

Practical tips, classic vectors, and how this differs from plain Base58

Use sibling plain Base58 when you only need alphabet conversion without checksums; use this Base58Check capability when integrity matters. Prefer encode when you hold a version-prefixed hash or other binary payload in hex and need a paste-safe string with integrity; prefer decode when you already hold a Base58Check address-like string and must recover the payload only if the checksum is intact. Round-trip smoke tests are straightforward: encode the well-known hex payload zero zero zero one zero nine sixty-six seventy-seven sixty zero six ninety-five three D fifty-five sixty-seven forty-three nine E five E thirty-nine F eight six A zero D twenty-seven three B E E and confirm the result sixteen U w L L nine R i s c three Q f P q B U v K o f H m B Q seven w M t j v M, then decode that string and confirm payload_hex and checksum_hex d six one nine six seven f six. Deliberately flip the last character of a valid string and assert that your client handles invalid_input with a message that names both the received and expected four-byte checksums. Keep requests under the published character limit; extremely long payloads expand as big integers and are better split offline. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when you fuzz bad checksums. When teaching, show the same payload encoded with and without the checksum so learners see why Bitcoin-style strings are longer and why a single-character typo almost always fails closed instead of opening the wrong wallet.