Base62
The densest safe alphabet: 0-9A-Za-z.
Where it came from
Base62 takes Base36 and adds lowercase letters, using the full 62-character alphanumeric set. It is the sweet spot for unique IDs: denser than Base36, yet still free of +, / and = that make Base64 hostile to URLs.
URL shorteners (bit.ly), YouTube (mixed case IDs), and Snowflake-style primary keys all lean on Base62 to pack big integers into short, copy-paste-safe strings.
How it works
Each character encodes log2(62) ≈ 5.95 bits. Conversion is repeated division by 62, mapping remainders to 0-9A-Za-z. No padding needed, no reserved characters.
UWC encodes bytes to Base62 and decodes them back in your browser. It is the go-to when you need compactness without URL-escaping headaches.