base64urlencoded

Base64url encoded, or base64url, refers to a variant of Base64 encoding designed for use in URLs and filenames. It uses the same 64-character set as Base64 but replaces the two characters that are problematic in URLs and filenames: '+' becomes '-' and '/' becomes '_'. In many contexts padding '=' characters are also omitted. The format is described in RFC 4648 as base64url.

Compared with standard Base64, base64url changes the alphabet and often removes padding. Decoding base64url requires a decoder that understands the URL-safe character set and, if padding is omitted, uses the input length to determine the proper block size. Some implementations accept both padded and unpadded input.

Base64url is widely used in web-related technologies where data must be placed in URLs or query strings without escaping. It is commonly used in JSON Web Tokens, OAuth 2.0, OpenID Connect, and certain API signatures. It preserves the data while ensuring URL safety and filename safety.

Example: the ASCII string Hello encodes in standard Base64 as SGVsbG8=; in base64url form it is typically written as SGVsbG8 (no padding). Some systems keep the padding, yielding SGVsbG8=. The choice depends on the specific protocol or library.