Base62 decode
Base62 decode. Runs on your device, nothing is uploaded.
Base62 decode reads digits and both cases of letters under this build's own alphabet, 0-9 then A-Z then a-z, as one big number and converts it back to bytes. A leading run of the alphabet's first symbol, 0, becomes that many zero bytes up front, the rule decode-base58 also applies. An unrecognised character halts the run and names its position.
Questions
What alphabet does it use?
This build's own base62 alphabet: digits 0-9, then uppercase A-Z, then lowercase a-z.
How are leading zero bytes handled?
Each leading character equal to the alphabet's first symbol, 0, becomes one leading zero byte in the output.
What happens with an invalid character?
The tool refuses, naming the character and its offset.
Is there a standard base62 spec?
No single de facto one; this is the same big-integer technique decode-base58 uses, applied to a 62-symbol alphabet.
Can I use this from the command line?
Yes, the same code runs on the page, the CLI and MCP.