Putting It All Together

You've built every layer:

Beyond:

• Base85 (Ascii85): 4 bytes → 5 chars (vs 3 → 4 in base64). Smaller. Used in PDF and Git binary patches.
• Base91 / yEnc: even smaller for binary-in-text. Niche.
• Hex: simpler but 2x overhead instead of 1.33x.
• Base32 / Base32-Crockford: case-insensitive variants for human-typeable data.
• MIME quoted-printable: efficient for mostly-ASCII data with occasional binary.

When NOT to use base64:

• Files for which native binary works (HTTP body, gRPC)
• Storage (33% bigger)
• Hot loops (encoding overhead)

Where you've seen it:

• Email attachments (MIME)
• Data URIs (data:image/...;base64,)
• HTTP Basic auth
• JWT
• PEM-encoded keys/certificates
• TOTP secrets (Base32)