Warning, the title of this post is a little bit misleading. It isn’t just one-click to get cleanly formatted code, it’s actually two. There are two things seasoned programmers will tell new programmers, that they don’t understand (at first):
  1. Always comment your code
  2. Properly indent code
The problem?  As a new programmer, you might not know how to do #2 until you get some experience.

How indenting helps

The reason you indent code is to make it easier for a reader to understand the code’s flow.  A compiler (well except in Python) doesn’t care if two lines line up or not.  The recent issues around Apple’s “goto fail;” are a great example of how indentation is meaningless to a C compiler. Looking at the following example, it is pretty clear (to humans) that line 1 is a decision point and lines 2-3 belong with line.

if (sensorValue > 100) {
   warningFlag = true;
Most modern code development environments try to help with proper formatting, and the Arduino IDE is no different. However, the IDE isn’t proactive as some of the more professional-focused tools. For this reason, one of the least used, yet very powerful features of the IDE is hidden in the Tools menu. The magic command won’t remove extra spaces between lines, but it’ll reformat some pretty messy things.
Arduino Autoformat Example with CTRL-T
A little help with CTRL-T
The image above shows how it takes the non-formatted code and turns it into something far, far more readable.

One Caution

The only thing i don’t like is how it handles “else” blocks.  I prefer to write my else blocks like this:

if (something) {
   // Do It!
} else {
  // Don't!
and it’ll format them into this:

if (something) {
   // Do It!
else {
  // Don't!
Not a huge difference and both are readable. For me, it is just personal preference to keep the braces (or brackets?) along with the else.

Where is it at?

How do you access this wonderful command?  It’s “hidden” in the tools menu.     Arduino Tools Window The keyboard shortcut is Ctrl-T (Win/Linux) or Cmd-T (Mac) and it is under the Tools Menu.  Before I compile code, I almost always hit the keyboard shortcut to see the result. Since I focused on the Arduino IDE, let me know if other environments offer this kind of clean up in the comments.

Fan of making things beep, blink and fly. Created AddOhms. Stream on Twitch. Video Host on element14 Presents and writing for Hackster.IO. Call sign KN6FGY.


  1. William C. Morgan Reply

    Using Linux 16 and Chromebook, with early version of Arduino installed with Crouton, Auto Format not only realigned the text but also told you if you were missing a { or } or had too many } or {.

    The newer version of Arduino on Gallium OS installed with Chrx allows only formatting the text without telling you the {} status.
    This is a minor point but I used the Auto Formatter as a trouble shooting tool.

    Is there any way of modifying the formatter tool to make this check for {} using Linux or is the formatter only realigning text on new versions of Arduino?

  2. The logic is that you put “else” exactly below the “if” to which it belongs, so the block of statements under “if” clearly “belongs” to the block of “else” statements.
    I think this comes from the way that block structured programming was taught in the late 70s/early 80s. Working in pseudocode and/or Pascal, as we did in those lessons, you would (be told to) use a lot of indentation and vertical space:

    if (test) then
          indented lines of code to show what the "if" was doing
          indented lines of code to show what the "else" was doing

    Lots of space used, but you knew what belonged with what! (and so did your teacher, it’s far easier to debug.)
    Nobody seems to format code like that nowadays, all been reading K&R and programming html, so putting a squiggle straight after the “if” test, making it less obvious where the end squiggle belongs, seems like a good idea because they’ve always done it.

    • Comments strip out a lot of formatting.
      This might have worked:

      Wrapping stuff in the HTML "pre" tags.

      Yup… that does work. Fortunately, the formatting you did gets stored, just not displayed. I edited your original comment.

      • Thank you. It wasn’t obvious that html would have worked, and I’m rubbish at html, anyway!
        Delete this at your own pleasure after reading!

  3. What the IDE lacks, or I can’t find, is the character position in the line – i.e.,, you get the line number down the bottom of the page, but not the character position.I tried Auto Format once and it made a complete hash of it. Notepad++ is much clearer when it comes to finding the closing bracket of a long if statement and I like the tab positions being shown. If you have a long sketch thrown together like mine, you tend to lose track of how many nested ifs, fors etc you have. I’ve just tried Auto Format again on some expendable code and if you line up everything on the left-hand side, then use Auto Format, it works quite well, assuming of course you haven’t missed out a few closing brackets.

  4. Thank you for pointing it out, I didn’t know the Arduino IDA had it.
    I don’t know which types of IDE you mean, but the bigger ones like Visual Studio, Eclipse or Netbeans do that.
    I work a lot with Eclipse and there you can set formatting as a “save action”, this means, your code is automatically formatted while saving. Also, you can set the formatting behaviour, so like you said the if-else thing (to be on separate lines or not), if there should be blanks beneath parentheses
    (like func( param ) or func(param) or func (param)) and whatnot else. You can also make missing comments on classes, public constants and functions cause a warning!

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