UTF-8 Base64
What this is
Base64 is an encoding of bytes, not of 'characters'. Unicode must become UTF-8 bytes first. If a tool uses escape() or charCodeAt without TextEncoder, Ada Lovelace’s name in Hindi will round-trip wrong.
Open the encoder — UTF-8 and base64url, no upload.
FAQ
- BOM?
- Do not prefix UTF-8 with a BOM for JSON or JWT. It will show up as  after a naive decode.