What does this tool remember, and where?

A decoder that keeps a history is convenient and quietly risky, because the thing it would be keeping is the decoded output — and decoded output is routinely a token, a password or a private key. It is worth knowing what any tool you use retains, and where that retained copy lives.

This one keeps a short record of recent activity in your own browser, on this device, and it never leaves. Each entry notes how many layers were peeled, which direction the conversion went, how large the result was, when it happened, and a preview of the first 64 characters. Your appearance preference is stored the same way. Nothing is kept anywhere else, because there is no server to keep it on.

Full payloads are never stored. The preview is cut before the entry is written rather than trimmed afterwards, and every stored field has a hard size limit, so a payload would not fit even if something went wrong upstream. A history that quietly retained credentials would be worse than having no history at all, which is why the truncation is a property of how entries are created rather than a cleanup step that could be skipped.

Clearing it removes everything immediately. Your browser’s own settings for clearing site data do the same, and closing a private window discards it without any action from you.

You can verify all of this on any tool, not just this one. In your browser’s developer tools, open the storage or application panel and look at local storage for the site. Everything the page has kept on your machine is listed there in plain text, including anything it did not tell you about.