Base64 Encoder / Decoder

Full UTF-8 support. URL-safe variant. Pure browser — nothing is sent anywhere.

Output

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What Base64 is for

Base64 encodes arbitrary binary data using only ASCII characters that survive being copy-pasted through email, JSON, URLs, and shell commands. It's not encryption — anyone can decode it. Common uses: embedding images in CSS data URIs, encoding API tokens, sending binary payloads through text-only protocols.

The size cost

Every 3 bytes of input become 4 characters of output — so Base64-encoded data is ~33% larger than the original. Not a big deal for short tokens; meaningful for large files (which is why HTTP uses gzip).

URL-safe variant

Standard Base64 uses + and /, both of which need URL-encoding in query strings. The URL-safe variant (RFC 4648 §5) substitutes - and _ and drops the = padding. Standard JWT tokens use this variant.