Paste Base64 and read what is inside. Every space and line break is stripped before decoding, so a value copied straight out of an HTTP header or a config file works without tidying it up first. The bytes are then read as UTF-8, so accented letters and emoji come out the way they went in, and the result appears as you type.
This page loads no libraries at all. The work is done by the browser itself. Your file is read on your own machine and never sent anywhere. Open your browser’s network tab and watch while you use it.
The standard alphabet only is accepted: A–Z, a–z, 0–9, + and /, so URL-safe Base64, which uses - and _ instead, is refused; a JWT segment is the usual case. A string that was merely cut short normally decodes anyway, to a shorter result, and fails only when a single stray character is left over.
No. The data:image/png;base64, part in front is not Base64, and one character outside the alphabet fails the whole string. Remove everything up to and including the comma and the rest will decode, though if it was an image, what comes back is unreadable text rather than a picture.
No. The bytes are handed to a UTF-8 reader, so a PNG comes back as replacement characters mixed with stray letters and control codes, and no error is raised. This page writes text and nothing else. There is no image preview on it.
The count is of the decoded bytes, not of the characters. UTF-8 spends two bytes on an accented letter and up to four on an emoji, so the example on this page reads as twenty-one characters and reports thirty-five bytes.
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