Base64 is an encoding scheme that converts binary data into a string of 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). It is widely used to embed binary content — like images, PDFs, or arbitrary bytes — inside text-based formats such as JSON payloads, HTML data URLs, email attachments (MIME), and JWTs. It is an encoding, not encryption — it does not provide any security.

Base64 encodes every 3 bytes of input into 4 ASCII characters. This 4:3 ratio — combined with optional padding — means the output is approximately 133% of the input size (a ~33% overhead). When you add MIME line-breaks every 76 characters, the overhead increases slightly further. This trade-off is worthwhile when the transport layer only supports text.

A data URL (also called a data URI) embeds file content directly into a URL string using the format data:[mime-type];base64,[base64-data]. Browsers can render a data URL as an <img> src, a CSS background-image, or an anchor href — no server required. They are ideal for small images or icons that you want to inline into HTML or CSS to save an HTTP request.

Standard Base64 uses + and /, which have special meanings in URLs (+ is a space, / separates path segments). RFC 4648 defines a URL-safe variant that replaces + with - and / with _. This makes the output safe to embed in query strings or path segments without percent-encoding. JWTs, for example, use URL-safe Base64 without padding.

Yes. The File → Base64 tab accepts any file type via drag-and-drop or file picker. It reads the raw bytes using FileReader.readAsDataURL(), then extracts the Base64 payload. The Base64 → File tab reverses the process: it decodes the Base64 string back to a Uint8Array, creates a Blob with the correct MIME type, and triggers a browser download via URL.createObjectURL. Everything stays in your browser — no upload occurs.