Developer utilities
Base64 Encoder & Decoder
Encode text to Base64 or decode Base64 back to text, including base64url.
Output uses the standard + and / alphabet with = padding. Everything runs locally in your browser, up to 1,000,000 characters. Nothing is sent to the server or stored.
Results appear here. Paste text or Base64 and the conversion runs automatically.
How to use the Base64 encoder and decoder
- Choose Encode to turn text into Base64, or Decode to turn Base64 back into text.
- Paste into the input box, or select Example to load a sample value.
- The conversion runs automatically as you type and the result appears below.
- Use Copy to put the output on your clipboard.
Encoding and decoding run entirely in your browser and are never sent to FKINFAST servers. Nothing you paste is stored, logged or shared.
Base64, base64url and padding
Base64 represents arbitrary bytes using 64 printable characters. Every three bytes become four characters, so Base64 output is about 33% larger than the original data. Padding with = completes the final group when the input length is not a multiple of three.
- Standard Base64 uses
+and/and keeps the=padding. - URL-safe Base64 (base64url) uses
-and_instead, and this tool omits padding, which is the common form in JWTs and URLs. - The decoder accepts both alphabets, with or without padding, and ignores spaces and line breaks.
- Base64 is not encryption and not compression. Anyone can decode it, and it always makes data larger.
Common Base64 errors and how to fix them
- Invalid character
SGVsbG8!Remove or replace the stray character. Base64 uses A–Z, a–z, 0–9, + and / (or - and _ for base64url).- Wrong padding
Zg=Padding completes the final group: Zg== for one byte, Zm8= for two bytes, or no padding at all. This decoder accepts either.- Mixed alphabets
w7/Dv_Standard Base64 uses + and /; base64url uses - and _. Convert the value to one alphabet before decoding.- Decoded output looks like garbage
iVBORw0KGgo…That is valid Base64 for binary data, not text. Use a file-aware tool; this page only displays UTF-8 text.- Truncated input
SGVsbG8A Base64 group cannot be a single character. Re-copy the full value, including padding if it had any.
Base64 FAQ
Is Base64 encryption?
No. Base64 is a reversible encoding, not a security measure. Never use it to protect passwords, tokens or personal data; use TLS in transit and real encryption at rest.
Does the encoder handle Unicode and emoji?
Yes. Text is converted to UTF-8 bytes before encoding, so accents, emoji and other non-ASCII characters round-trip correctly. Decoding fails with a clear message when the bytes are not valid UTF-8 text, which usually means the value is binary.
Why does my decoded value contain replacement characters?
It should not: this tool rejects invalid UTF-8 instead of substituting replacement characters. If another decoder shows �, the underlying bytes are not UTF-8 text.
Is there an input size limit?
The in-browser converter accepts up to 1,000,000 characters per conversion so the page stays responsive. Use a command-line tool for larger payloads.