Base64 in APIs: start with the alphabet.

Base64 represents bytes using printable characters. Three bytes become four characters; padding marks an incomplete final group. Encoding is reversible and does not conceal a credential.

Standard or URL-safe?

Standard Base64 uses letters, digits, + and /. Base64url substitutes - and _. Some protocols omit trailing =. Match your API documentation rather than assuming the two formats are interchangeable.

A JSON round trip

The text {"ok":true} encodes to eyJvayI6dHJ1ZX0=. Decode it here to see the original text. Format JSON adds indentation to a separate view; switch back to Raw text to copy the original decoded value.

Whitespace and key order can matter to signatures even when two objects have the same meaning. Encoding a formatted view changes the bytes. Use raw text when reproducing a signed payload.

JWT segments

A compact signed JWT has dot-separated segments. Its header and payload use Base64url; decode one segment at a time. Decoding does not verify the signature or establish that any claim is trustworthy. This tool is not a token validator.

Reference: RFC 4648. Open the converter.