Base64 エンコード・デコードツール

What is Base64 encoding?

Base64 is a way of representing binary data using only 64 printable ASCII characters (A to Z, a to z, 0 to 9, plus "+" and "/"). It works by taking three bytes (24 bits) at a time and splitting them into four 6-bit groups, each mapped to one of those 64 characters. The result is text that can travel safely through systems that were designed for text and might otherwise corrupt raw binary.

When should you use Base64?

Base64 shows up wherever binary data needs to ride inside a text-only channel: embedding small images in CSS or HTML with data URIs, attaching files to email (MIME), encoding credentials in HTTP Basic Auth, and storing binary blobs in JSON or XML. It is the standard answer to "how do I put bytes where only text is allowed".

Base64 is not encryption

A crucial point: Base64 is encoding, not encryption. It provides no security whatsoever. Anyone can decode it back to the original in seconds, exactly as this tool does. It only changes the representation of data, not its secrecy. Never use Base64 to "hide" passwords or sensitive information; use real encryption for that.

Size overhead

Because Base64 represents 3 bytes with 4 characters, encoded data is about 33% larger than the original, plus a little padding. That tradeoff (bigger size in exchange for text-safety) is why you embed only small assets as Base64 and link to larger ones normally. This tool encodes and decodes both typed text and any file you select, entirely in your browser, so nothing is uploaded.