Start with the kind of data you have
Base64 represents bytes using a restricted text alphabet. The Base64 Encoder / Decoder first converts entered text to UTF-8 bytes, then encodes those bytes. This allows accented letters and other Unicode text to travel through systems expecting Base64 rather than treating each visible character as a single byte.
Choose Encode for ordinary text and Decode for an existing Base64 string. Keep the original input until you have checked the result. Base64 is reversible encoding, so placing a password or access key inside it does not hide that secret from someone who receives the string.
Verify a predictable result
Enter Hello in Input, select Encode, and process it. The expected output is:
SGVsbG8=Now copy that result into Input, select Decode, and process again. The expected text is exactly Hello, with the original capitalization. An added newline in the source text changes the encoded result because the newline has its own UTF-8 byte representation.
For a Unicode check, encode café, then decode the resulting string. You should recover café. This confirms the text round trip, although it does not prove that another application expects UTF-8. If a receiving system documents a different character encoding, use its specified workflow rather than assuming every Base64 payload represents the same text format.
Diagnose decode errors
The decoder ignores whitespace in the encoded input. It validates the ordinary Base64 alphabet and rejects content that cannot be decoded as valid UTF-8 text. A successful Base64 decode can still contain arbitrary binary bytes, so a JPEG, ZIP, or executable encoded as Base64 is not necessarily usable in this text decoder.
This tool’s general decoder uses ordinary Base64 characters. A token segment using the URL-safe - and _ alphabet belongs in the JWT Decoder when it is part of a supported token. URL percent encoding is a separate transformation; use the URL Encoder/Decoder for URL components.
Keep the output in its intended context
Input is limited to 250,000 characters, and processing stays in the browser. The result can be downloaded as base64-result.txt. Treat that file with the same care as the source text because encoding adds no confidentiality. For an image embedding workflow, Image to Base64 supplies a data URL with the media type instead of asking you to assemble that prefix manually.