Base64URL decode
Base64URL decode. Runs on your device, nothing is uploaded.
Base64URL decode first swaps the URL-safe - and _ characters for the standard + and /, then runs the same padding and length checks decode-base64 applies. A character outside the alphabet, or a tail that cannot pad to a multiple of four, gets refused with its position given. UTF-8 text prints directly; anything else comes back as a decoded.bin file.
Questions
How is this different from decode-base64?
It first swaps the URL-safe - and _ characters back to the standard + and /, then applies the exact same padding and length checks.
Is padding required?
No, the same optional-padding handling as decode-base64 applies.
What happens with an invalid character?
The tool refuses, naming the character and its offset.
What does the output look like?
Valid UTF-8 text prints directly; anything else downloads as decoded.bin.
Can I use this from the command line?
Yes, the same code runs on the page, the CLI and MCP.