What this tool does
It reads the contents of a C# string literal and returns the text they stand for. It decodes the escapes C# recognises — \n, \r, \t, \b, \f, \v, \0 and \a — along with \uXXXX, the code point form \u{1F600} and the hex form \xNN. A surrogate pair written out as \ud83d\ude00 is recomposed into the one character it encodes.
Anything else after a backslash comes back as the bare character: \q gives q, \\ gives one backslash.
Where C# differs
\a and \v are the two escapes C# has that Java does not, which makes them a reliable signal that a literal came out of C# rather than Java. Both are decoded here: \a gives the bell character U+0007, \v the vertical tab U+000B. The difference runs the other way too: C# has no octal escape at all, where Java and JavaScript both do. \101 is A in those two and comes back here as the three characters 101, because in C# \0 is a named sequence and the 101 that follows is just text.
What it does not do
The eight-digit \U0001F600 form is not recognised and comes back as the literal text U0001F600; use \u{1F600} or the surrogate pair. \e is likewise returned as the letter e.
\u{1F600} is not C# syntax either. C# has \uXXXX and the eight-digit \UXXXXXXXX, and no brace form at all; it is accepted here for convenience, exactly as in the Java tool, but csc would reject it. On this one character the tool and the language disagree in both directions — it reads a form C# does not have, and does not read the form C# does.
\x is read as exactly two hex digits, whereas C# accepts one to four. \x4142 is one character in C# but comes back here as A42 — a genuine divergence, and a reason the variable-length form is discouraged in C# style guides in the first place.
Finally, it decodes one literal’s contents, not a C# expression: nothing is concatenated, interpolation holes are left as written, and verbatim strings should not be passed through it at all.
Private by design
Everything runs locally in your browser with JavaScript. Your data is never uploaded, which makes the tool safe for sensitive content, and it keeps working offline.