Free Base64 Encoder / Decoder

How this tool computes its result

Encodes text via btoa(unescape(encodeURIComponent(text))), a three-step chain that first converts the string into a UTF-8 byte-safe percent-encoded form before running the browser's built-in binary-to-Base64 conversion — necessary because btoa() alone only handles Latin1 and throws on multi-byte UTF-8 characters. Decoding reverses the chain: decodeURIComponent(escape(atob(base64))). File encoding uses FileReader.readAsDataURL() and then strips the leading "data:<mime>;base64," prefix so only the raw payload remains. The stats panel reports original byte size (via Blob), encoded size, and overhead percentage computed as (encoded.length / original.length − 1) × 100.

Worked example

Encoding the text "Hello, World!" (13 characters) produces the Base64 string "SGVsbG8sIFdvcmxkIQ==" (20 characters, including "==" padding). The overhead stat computes (20/13 − 1) × 100 ≈ 53.8%, illustrating the tool's own tip that Base64 inflates payload size by roughly a third to a half depending on padding.

When not to use this tool

Base64 is an encoding, not compression or encryption — per the tool's own guidance, use it only when you need ASCII-safe transport (embedding binary in JSON, CSS, or URLs), not to shrink payloads or protect data confidentiality.

Common mistakes

• - Pasting a malformed Base64 string (wrong padding or invalid characters) into Decode mode — atob() throws internally and the tool surfaces only the generic message "Error decoding: Invalid Base64 string" rather than pointing at the specific bad character or offset.
• - Expecting the file-encode output to include the "data:image/png;base64," style prefix for direct use in an <img src> — the tool deliberately strips that prefix, returning only the raw payload, so you must re-add a data URI prefix yourself if that's the intended use.
• - Assuming encoding reduces file size for storage or transfer — the tool's encoded output is always larger than the original, as shown by the overhead percentage it reports.

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