Base64 Guide: Encoding, Decoding, and Use Cases

Base64 converts binary to text

Base64 encodes binary data as ASCII text using 64 printable characters. It appears in data URIs, email attachments (MIME), JWT payloads, API credentials, and anywhere binary data must travel through text-only channels.

Zovaty Base64 Tool

The Base64 tool encodes and decodes text and files locally in your browser. Paste text to encode, paste Base64 to decode. Nothing is uploaded to a server.

How Base64 encoding works

Base64 groups every 3 bytes (24 bits) into 4 characters (6 bits each). Padding with = characters handles input lengths not divisible by 3. The output is roughly 33% larger than the original binary data.

Common use cases

Data URIs: embed small images in CSS or HTML

JWT tokens: header and payload segments are Base64url encoded

API authentication: Basic auth credentials encoded in headers

Email attachments: MIME encoding for binary files

Storing binary in JSON or XML text fields

Base64 vs Base64url

Standard Base64 uses + and / characters, which conflict with URL syntax. Base64url replaces + with - and / with _. JWTs use Base64url. Standard Base64 appears in data URIs and MIME. Know which variant your system expects.

Base64 is not encryption

Base64 is encoding, not encryption. Anyone can decode it instantly. Never treat Base64-encoded credentials as secure. Use proper encryption (TLS, AES) for sensitive data in transit and at rest.

Related Zovaty tools

Base64 tool — encode and decode

JWT decoder — inspect Base64url JWT segments

URL encoder/decoder — URL-safe encoding

Hash generator — one-way hashing (not encoding)

Conclusion

Base64 is a text-safe transport format, not security. Encode and decode instantly with the Base64 tool on Zovaty — local, free, and private.

Step-by-step encoding process

Base64 splits input into 3-byte groups (24 bits). Each group maps to 4 characters from the 64-character alphabet (A-Z, a-z, 0-9, +, /). Remainder bytes get padded with = characters. Decoding reverses this process.

Data URIs in web development

Data URIs embed small assets directly in HTML or CSS: img src="data:image/png;base64,...". Useful for tiny icons and critical CSS inlining. Avoid for large images — they bloat HTML and cannot be cached separately.

Debugging Base64 in APIs

API errors involving Base64 usually mean wrong padding, wrong alphabet (standard vs url-safe), or encoding text with wrong character set. Decode in the Base64 tool to inspect the actual content and identify the mismatch.

Base64 in email (MIME)

Email attachments are Base64 encoded within MIME multipart messages. The encoding adds 33% overhead to attachment size. Modern email systems handle this automatically, but understanding Base64 explains why email attachments are larger than the original files.

Storing binary data in text databases

Some systems store binary data as Base64 strings in text columns when binary column types are unavailable. This works but increases storage by 33% and requires encode/decode on every read. Prefer binary storage when your database supports it.

Base64 edge cases

Unicode text must be UTF-8 encoded before Base64 encoding. Newlines in encoded output may need stripping for URL embedding. Padding characters may need removal for URL-safe variants.

Encoding binary files

Small binary files (icons, certificates) can be Base64 encoded for embedding in config files or environment variables. Large files should remain as files — Base64 encoding increases size by 33%.

Base64 in API authentication

HTTP Basic Authentication encodes username:password as Base64 in the Authorization header. This is encoding, not encryption — always use HTTPS. For production APIs, prefer token-based auth over Basic Auth.

Debugging Base64 issues

Common failures: wrong padding, wrong alphabet (standard vs url-safe), UTF-8 not encoded before Base64, newlines in encoded string. Decode in the Base64 tool and inspect raw output to identify the issue.

Summary: Base64 essentials

Encoding not encryption. Use for text-safe binary transport. Decode to debug API issues. Encode/decode with Base64 tool locally.