Encode text to Base64 or decode it back — UTF-8 safe, with a URL-safe variant — using the full 64-character alphabet and padding rules printed on the page. Runs entirely in your browser — your numbers never leave this device.
| Characters / input case | Index / output | Notes |
|---|---|---|
| A–Z | 0–25 | Uppercase letters open the alphabet |
| a–z | 26–51 | Lowercase letters follow |
| 0–9 | 52–61 | Digits come next |
| + | 62 | Standard alphabet — written - in the URL-safe variant |
| / | 63 | Standard alphabet — written _ in the URL-safe variant |
| = (padding) | No value | Pads the output to a multiple of 4 characters |
| 1 leftover byte | 2 characters + == | The last group carries 8 real bits in 2 characters |
| 2 leftover bytes | 3 characters + = | The last group carries 16 real bits in 3 characters |
| 0 leftover bytes | 4 characters, no padding | The byte count was an exact multiple of 3 |
Base64 exists to carry binary data through channels that only handle safe text — email, URLs, JSON strings, data URIs. The method is a regrouping, nothing more: take the bytes three at a time, split each 24-bit group into four 6-bit numbers, and write each number as a character from the 64-character alphabet in the table below. Text is first encoded as UTF-8 bytes, so accented letters and emoji survive the round trip — the café example below is nine UTF-8 bytes, not seven characters, and the output length follows the bytes.
Two conventions decide whether a decoder accepts your string. First, padding: when the byte count is not a multiple of three, equals signs pad the output to a multiple of four characters, and the count of equals signs tells the decoder how many bytes the last group really held. Second, the variant: the standard alphabet ends in + and /, which are dangerous inside URLs, so the URL-safe variant swaps them for - and _ and usually drops the padding. This tool offers both, and decoding rejects characters outside the chosen alphabet instead of guessing.
One honest warning, because it is the most common misunderstanding of this tool: Base64 is an encoding, not encryption. Anyone who sees a Base64 string can decode it instantly — it hides nothing, it only makes bytes transportable. And like every Kwikfig tool, the conversion runs in your browser; the text you encode never leaves your device.
Because each output character carries only 6 bits while each input byte holds 8. Four characters carry three bytes, so the encoded size is 4 × ceil(bytes ÷ 3) — a 7-byte word like Kwikfig comes out at 12 characters, and a 300 KB file at roughly 400 KB of text. That overhead is the price of using only safe, printable characters.
It is the same encoding with the two URL-hostile alphabet characters swapped (+ becomes -, / becomes _) and the = padding usually dropped. Use it when the encoded value travels inside a URL, a filename or a token. Use the standard alphabet everywhere else, because some strict decoders expect the padding to be present.
No. Base64 is a public, reversible encoding with no key — anyone can decode any Base64 string in a second, including with this very page. It is suitable for transporting data, never for protecting it. Passwords, tokens and private text need real encryption or hashing, not an encoding.
Usually one of three reasons: the string contains characters outside the Base64 alphabet (a standard string pasted into a URL-safe decoder, or the other way round), whitespace or line breaks were copied inconsistently, or the string was truncated so its length and padding no longer agree. This tool names the problem instead of returning corrupted bytes.
Yes, because text is converted to UTF-8 bytes before encoding and decoded back as UTF-8 afterwards. That is why café ☕ encodes to Y2Fmw6kg4piV and returns exactly. Tools that treat text as single-byte Latin characters corrupt anything beyond plain ASCII — the byte count is the tell: 7 characters became 9 bytes.
No. Encoding and decoding run entirely in your browser — the text never leaves your device and is not stored or tracked.
More in Developer Tools · Browse all tools