Base64 Encode / Decode

Base64 is a binary-to-text encoding scheme that represents binary data (like files, images, or raw bytes) as a string of printable ASCII characters. It was defined in RFC 4648 and is used pervasively across web development, email protocols, APIs, and security systems — anywhere binary data needs to be safely embedded in a text context.

The encoding works by taking every 3 bytes of binary input and converting them into 4 Base64 characters drawn from an alphabet of 64 characters: A–Z, a–z, 0–9, +, and /. Padding = characters are appended when the input length is not a multiple of 3. The result is always approximately 33% larger than the original but guaranteed to contain no special characters that might be misinterpreted by parsers, HTML renderers, or network protocols.

Where Base64 is used in practice

Data URIs: Images, fonts, and small files can be embedded directly into HTML or CSS as Base64-encoded data URIs (data:image/png;base64,...), eliminating additional HTTP requests. This is a common optimization for small icons in email templates where external URLs may be blocked.

Email attachments (MIME): The SMTP email protocol only transmits 7-bit ASCII text. Binary files attached to emails are Base64-encoded before transmission and decoded by the recipient's email client. Without Base64, PDF attachments or images could not travel through email.

JWT tokens: JSON Web Tokens encode their header and payload sections as Base64URL (a URL-safe variant using - and _ instead of + and /). Decoding the middle section of a JWT with a Base64 decoder reveals the user claims and metadata inside the token (see also our JWT Decoder).

Basic HTTP Authentication: The Authorization: Basic <credentials> header encodes username:password as Base64 before sending. Note this is encoding, not encryption — it should only be used over HTTPS.

API responses and webhooks: Many APIs return binary content (images, documents, audio) encoded as Base64 strings within JSON responses, since JSON cannot natively represent binary data.

Storing binary data in text fields: Base64 is used to store certificate public keys in PEM files (the -----BEGIN CERTIFICATE----- format), SSH public keys, and configuration blobs in YAML/JSON config files.

Encoding vs decoding

Encoding converts raw text or binary to a Base64 string. Decoding reverses the process — it converts a Base64 string back to the original content. If the Base64 string is malformed (wrong padding, invalid characters), decoding will fail with an error, which is useful for verifying that a Base64 value is well-formed before using it.

The UtilsGo Base64 tool runs entirely in your browser. Credentials, private keys, and sensitive values you encode or decode are never transmitted to any server.