Base64 Encode / Decode — No Server, No Upload, Instant
Encode text to Base64 or decode Base64 back to text instantly. Handles Unicode and emoji correctly. Runs in your browser using built-in JavaScript — nothing is sent to any server.
How to use this tool
- Paste text or enter the string to encode.
- Choose Encode or Decode.
- Copy the Base64 result.
About Base64 Encoder / Decoder
Base64 is a binary-to-text encoding that represents arbitrary data using only 64 printable ASCII characters: A–Z, a–z, 0–9, plus + and /. It works by taking three bytes (24 bits) at a time and splitting them into four 6-bit groups, each of which maps to one character. When the input length is not a multiple of three, the output is padded with one or two = characters. The result is roughly one third larger than the original, which is the price you pay for making binary data survive transport channels that only handle text.
The reason Base64 exists is that many systems were designed for text and will corrupt or strip raw bytes. Email bodies, JSON string values, HTTP headers, and URLs cannot reliably carry arbitrary binary content, but they can carry the safe character set Base64 produces. That is why you see it in data URLs that embed images directly in HTML or CSS, in email attachments, in API payloads that need to ship a small blob inside a JSON string, and as the encoding underneath HTTP Basic authentication headers.
This tool encodes and decodes text rather than files, and it handles Unicode correctly — a detail many naive implementations get wrong. The browser's built-in btoa function only accepts characters in the Latin-1 range, so accented letters, non-Latin scripts, and emoji would otherwise throw an error. The tool first UTF-8 encodes the text before applying Base64, and reverses that on decode, so any Unicode input round-trips faithfully. If decoding fails, it is almost always because the input is not valid Base64 — for example, it contains characters outside the alphabet or has incorrect padding.
A crucial caveat: Base64 is encoding, not encryption. It provides zero confidentiality, because anyone can decode it instantly with no key. Treat it purely as a transport format, never as a way to hide secrets. Also note that standard Base64 uses + and /, whereas the URL-safe variant (used in JWTs and many tokens) substitutes - and _ and drops padding; the two are not interchangeable without conversion. Everything here runs locally in your browser, so the text you paste is never transmitted.
Frequently Asked Questions
- Is Base64 a form of encryption?
- No. Base64 is reversible encoding with no secret key, so anyone can decode it instantly. It provides no confidentiality whatsoever and must never be used to protect passwords, tokens, or any sensitive data. Its only job is to represent binary or special-character data using a safe, text-friendly character set.
- Does this handle Unicode characters and emoji?
- Yes. The text is UTF-8 encoded before Base64 conversion and decoded the same way in reverse, so accented letters, non-Latin scripts, and emoji round-trip correctly. This avoids the common bug where a raw btoa call throws an error on any character outside the Latin-1 range.
- Why does my Base64 string fail to decode?
- Decoding fails when the input is not valid Base64 — it contains characters outside the A–Z, a–z, 0–9, +, / alphabet, has the wrong number of padding = characters, or is actually URL-safe Base64 using - and _. Check for stray whitespace, line breaks, or that you have not mixed up the standard and URL-safe variants.
- What is the difference between standard and URL-safe Base64?
- Standard Base64 uses + and / and pads with =. URL-safe Base64, used in JWTs and many web tokens, replaces + with - and / with _ and usually omits the padding so the string is safe inside URLs and headers. The two are not directly interchangeable; you must convert the characters before decoding the other variant.
- Why is the encoded output longer than my input?
- Base64 encodes every three bytes of input as four output characters, so the result is about 33 percent larger than the original. That overhead is the cost of restricting the output to a small, transport-safe character set. It is why Base64 is used for compatibility, not for saving space.
- Can I encode an image or other binary file here?
- This tool encodes and decodes text. To Base64-encode a binary file such as an image for use in a data URL, you would use the browser's FileReader API or a dedicated file-to-Base64 converter, since that path reads raw bytes rather than a typed string.
- Is my input sent to a server?
- No. Both encoding and decoding use the browser's built-in functions and run entirely on your device. Nothing you paste is uploaded or logged, so it is safe to use even with content you would not want to leave your machine.
How to Encode and Decode Base64 Without Uploading
Encode or decode Base64 strings in your browser using btoa()/atob() — zero network transmission. Includes coverage of Base64Url, JWT encoding, and Unicode handling.
Best Base64 Encoder/Decoder Tools That Don't Upload Your Data (2026)
Comparison of client-side Base64 tools — no server transmission, verified in DevTools. Covers when Base64 privacy matters, Base64Url, and browser console alternatives.
Embed this tool on your site
Free. One line of HTML — the tool runs in your visitor's browser, no data sent to anyone.
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