UBB, also known as BBCode, is the square-bracket markup used by classic forums and bulletin boards because it is safer to allow than raw HTML. This tool converts the common tags — [b] [i] [u] [s] [url] [img] [color] [size] [quote] [code] and [url=…] link forms, plus blank-line paragraphs — into the equivalent HTML, so you can preview forum posts or migrate content to a plain web page.
The reverse direction maps the matching HTML tags (strong/b, em/i, a, img, blockquote, font color/size, and line breaks) back into BBCode. Conversion is done with straightforward tag replacement, and everything runs locally in your browser — your text is never uploaded to any server.