Toggle Line Comments

About this tool

Commenting out a block of code is a one-keystroke job inside an editor and a fiddly one everywhere else. Code pasted into a chat window, a ticket, a code review, a snippet manager, or a docs draft has left the editor behind, so the markers have to go on — or come off — by hand, one line at a time, in whichever syntax that language happens to use.

This tool does what Ctrl+/ does. Paste a block, pick a language (or leave Auto-detect on), and every line gets the right marker: // for JavaScript, TypeScript, Java, C#, C, C++, Go, Rust, Swift, Kotlin, Scala, and PHP; # for Python, Ruby, Perl, shell, PowerShell, YAML, TOML, R, Dockerfiles, and Makefiles; -- for SQL, Lua, and Haskell; ; for INI; ;; for Clojure; % for LaTeX; ' for Visual Basic; and REM for batch files. CSS, HTML, and XML have no line comment at all, so each line is wrapped in /* */ or <!-- --> instead.

Toggle is the default and follows the editor rule: if every line under consideration already carries the marker, the block is uncommented; otherwise the whole block is commented. A partly commented block therefore becomes fully commented rather than half-inverted, which is what makes the operation reversible — run it twice and you are back where you started. Comment every line and Uncomment every line force a direction when you want one.

With the defaults, this:

  if ready:
      send(payload)
  log("done")

becomes this:

  # if ready:
  #     send(payload)
  # log("done")

The marker lands at the block's shallowest indentation, so relative indentation survives and the code still reads as code. Choose Flush left at column 0 if you prefer every marker pinned to the left margin, which is the other convention editors offer.

Three smaller controls cover the rest. Space after the marker writes // code rather than //code and is on by default, because that is what most linters and formatters expect; uncommenting removes at most one such space, so deliberate indentation inside a comment survives a round trip. Also comment blank lines marks blank and whitespace-only lines too — off by default, matching editor behavior — and when on, a blank line becomes the bare marker with no trailing space. Custom marker overrides the language's own syntax for anything the list does not cover, such as an @ directive or a template language; a custom marker is always treated as a line comment, never as a pair.

Limits and edge cases:

• This is a lexical transform, not a parse. A // inside a string literal or a URL looks like a comment marker to the tool, so a line such as url = "https://example.com" will be treated as already commented if you point the JavaScript profile at it.
• Auto-detect is a heuristic over shebangs, existing comment markers, and distinctive keywords. It is deliberately conservative and falls back to # for a plain list of lines. Name the language when it guesses wrong.
• Uncommenting only removes the marker that the selected language (or custom marker) defines. Mixed syntax in one block needs one pass per syntax.
• Line endings are preserved, including CRLF, and the trailing newline of your input is left as you pasted it.
• Input is capped at 2,000,000 characters.
• Nothing is uploaded. The page runs the Rust/WASM transform in your browser.

FAQ