Paste your text into a browser-based HTML entity encoder and it converts characters like less-than, greater-than and ampersand into their safe entity equivalents such as <, > and &. Escaping happens on your device, and it is the correct way to show code or user text on a page without the browser trying to render it as markup.
A browser reads < and > as the start and end of tags, and & as the start of an entity. If you drop raw text containing those characters into HTML, the page either renders wrong or, when the text came from a user, becomes an opening for cross-site scripting. Escaping replaces each dangerous character with its entity, so it displays as a literal character instead of being interpreted as code.
The tool goes both ways. Encoding turns your text into entities so you can safely paste code samples into a blog post or documentation. Decoding turns entities back into their characters, which is handy when you copy text out of HTML source and want the plain version. Note that in a real application you should rely on your framework's escaping; this tool is for one-off snippets and understanding what the entities are.
The HTML-significant ones, chiefly less-than, greater-than, ampersand and quotes, become entities like <, >, & and ".
Yes. The tool encodes and decodes, so you can turn < back into a literal less-than sign.
No. Encoding and decoding run entirely in your browser.