What escaping does
JSON strings can't contain raw double quotes, backslashes, or line breaks. Escaping replaces them with safe sequences: a quote becomes backslash-quote, a newline becomes backslash-n, and so on. The result drops cleanly into a JSON value or a string literal in most programming languages without breaking the syntax.
When you need unescape
Sometimes you have an escaped string from a log file, an API response, or a JSON field that itself holds JSON, and you want the readable original. Unescape mode resolves the backslash sequences back into real quotes and line breaks. If the input has a broken escape sequence, it tells you instead of guessing.
Common situations
Embedding a block of JSON inside another JSON string. Pasting multi-line text into a config value. Copying a string out of code without mangling the quotes. Reading a doubly-escaped value from a log. Switch between escape and unescape with the toggle, and nothing leaves your browser.