The tooling is solid, the lsp server provides auto completions and edit by edit syntax checking in major editors like vim, Emacs and vscode, there is a good formatting tool in elm-format, a built in repl which is basic but works fast. A test runner is also there, with support for fuzzing. Not to mention a time travel debugger which is a highlight. Things that are missing or not good are proper logging, step by step line debugger, profiling and performance tracking.