The Elm REPL runs entirely in the browser, so it can also be used without internet:
elmrepl.de keeps working once it has been opened. Or download the zip file, unzip it
and open index.html in the browser. The folder can also be put on any web server.
The REPL gives the same results as elm repl, but error messages can differ in
details. Very large or deeply nested code (e.g. a list with more than about 1000 elements
written in the code) exceeds the limits of the compiler in the browser. Formatting uses a
port of elm-format that does not support all code.
Details
