Mar 14

This article was written by José M. Aguilar in Spanish on his excellent blog Variable Not Found, and was translated, edited and republished here by Timm Martin (and Google Translator) with permission from Mr. Aguilar.

Following are 13 tips on how to comment your source code so that it is easier to understand and maintain over time.

1. Comment each level

Comment each code block, using a uniform approach for each level.  For example:

  • For each class, include a brief description, author and date of last modification
  • For each method, include a description of its purpose, functions, parameters and results

Adopting comment standards is important when working with a team.  Of course, it is acceptable and even advisable to use comment conventions and tools (such as XML in C# or Javadoc for Java) to facilitate this task.

2. Use paragraph comments

Break code blocks into multiple “paragraphs” that each perform a single task, then add a comment at the beginning of each block to instruct the reader on what is about to happen.

// Check that all data records
// are correct
foreach (Record record in records)
    if (rec.checkStatus()==Status.OK)
        . . .
// Now we begin to perform
// transactions
Context ctx = new ApplicationContext();
. . .

3. Align comments in consecutive lines

For multiple lines of code with trailing comments, align the comments so they will be easy to read.

const MAX_ITEMS = 10; // maximum number of packets
const MASK = 0x1F;    // mask bit TCP

Some developers use tabs to align comments, while others use spaces.  Because tab stops can vary among editors and IDEs, the best approach is to use spaces.

4. Don’t insult the reader’s intelligence

Avoid obvious comments such as:

if (a == 5)      // if a equals 5
    counter = 0; // set the counter to zero

This wastes your time writing needless comments and distracts the reader with details that can be easily deduced from the code.

5. Be polite

Avoid rude comments like, “Notice the stupid user has entered a negative number,” or “This fixes the side effect produced by the pathetically inept implementation of the initial developer.”  Such comments do not reflect well upon their author, and you never know who may read these comments in the future: your boss, a customer, or the pathetically inept developer you just insulted.

6. Get to the point

Don’t write more in comments than is needed to convey the idea.  Avoid ASCII art, jokes, poetry and hyperverbosity.  In short, keep the comments simple and direct.

7. Use a consistent style

Some people believe that comments should be written so that non-programmers can understand them.  Others believe that comments should be directed at developers only.  In any event, as stated in Successful Strategies for Commenting Code, what matters is that comments are consistent and always targeted to the same audience.  Personally, I doubt many non-developers will be reading code, so comments should target other developers.

8. Use special tags for internal use

When working on code as a team, adopt a consistent set of tags to communicate among programmers.  For example, many teams use a “TODO:” tag to indicate a section of code that requires additional work:

int Estimate(int x, int y)
    // TODO: implement the calculations
    return 0;

Tag comments don’t explain code; rather they seek attention or deliver a message.  But if you use this technique, remember to follow up and actually do what the message is asking.

9. Comment code while writing it

Add comments while you write code and it’s fresh in your memory.  If you leave comments until the end, it will take you twice as long, if you do it at all.  “I have no time to comment,” “I’m in a hurry,” and “The project is delayed” are all simply excuses to avoid documenting your code.  Some developers believe you should write comments before code as a way to plan out your ultimate solution.  For example:

public void ProcessOrder() 
    // Make sure the products are available
    // Check that the customer is valid
    // Send the order to the store
    // Generate bill

10. Write comments as if they were for you (in fact, they are)

When it comes to commenting code, think not only about the developers who will maintain your code in the future, but also think about yourself.  In the words of the great Phil Haack:

“As soon as a line of code is laid on the screen, you’re in maintenance mode on that piece of code.”

As a result, we ourselves will be the first beneficiaries (or victims) of our good (or bad) comments.

11. Update comments when you update the code

There is no point in commenting correctly on code if the comments are not changed with the code.  Both code and comments must move in parallel, otherwise the comments will actually make life more difficult for developers who maintain your code.  Pay special attention to refactoring tools that automatically update code but leave comments unchanged and hence obsolete in the same instant.

12. The golden rule of comments: readable code

One of the basic principles for many developers: Let your code speak for itself.  Although one suspects this movement is led by programmers who do not like to write comments, it is true that self-explanatory code can go a long way toward making code that’s easier to understand and can even render comments unnecessary.  For example, the code in my Fluid Interfaces article shows how clear self-explanatory code can be:

Calculator calc = new Calculator();
Console.WriteLine( "Result: {0}", calc.Get() );

In this example, comments are not needed and would likely violate tip #4.  To facilitate readable code, you might consider using proper names (as described in the classic Ottinger’s Rules), ensure correct indentation, and adopt coding style guides.  Failure to comply with this tip may result in comments that seem to apologize for bad code.

13. Share these tips with your colleagues

Although tip #10 shows how we ourselves benefit immediately from good comments, these tips will benefit all developers, especially in the context of team working together.  Therefore, feel free to share these commenting tips with your colleagues to create code that is easier to understand and maintain.

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Article published on March 14, 2008

69 Responses to “13 Tips to Comment Your Code”

  1. Ferruccio Barletta Says:

    I would add one more tip that I’ve found very useful.

    The code should explain how. The comments should explain why.

    #12 comes tantalizingly close to this.

  2. cxfx Says:

    Nice article, my own thoughts on commenting:

  3. Chad Myers Says:

    Or, better yet, don’t do comments and make the code speak for itself rather than writing bad code that needs instantly-obsolete comments:

  4. Aaron Saray Says:

    I agree with most of the points made here to a T.

    One thing I can’t stand is the whole “write code better” or “code better” arguments going back and forth. From working in the Insurance industry, I’ve got my self elbows deep in complex calculations. No matter how much verbosity you use with your variables and how ‘well’ you write it, comments are absolutely 100% necessary.

    *hangs head* I’m sometimes guilty of jokes and profanity from time to time… but… I… *sigh* no excuses. 🙂

  5. Chad Myers Says:

    @Aaron: Complex algorithms and low-level munging, when justified and otherwise unavoidable would qualify for heavy commenting, in my opinion even though I’m pretty rabidly anti-Commenting (with exceptions for things like //TODO that tools can pick up and use).

  6. Finds of The Week - March 16, 2008 » Chinh Do Says:

    […] M. Aguilar has put together a very sensible list of 13 Tips to Comment Your Code. Translated and republished in English by Timm […]

  7. Eric Says:

    Remember, the most useful comment is the comment that does not have to be written!

    Never sacrifice code readability for performance unless the benchmarks tell you that you must. A fast-running, but convoluted and bug-filled algorithm is far worse than a slow-working, easy to maintain reliable one. I’m not advocating writing slow code, but CPUs keep getting faster and compilers keep getting more efficient. Complicated code will ALWAYS be hard to debug.

    Obviously if you have to loop over your slow code 10,000 times, do what you must to make it work and document it as little as necessary. Code can be tested, however comments cannot be tested, and there is nothing worse for a developer than comment-rot, i.e. software has been changed, but the comments do not reflect the changes.

    Use the most lines of code that make sense, write the fewest comments you can reasonably get by with.

  8. Reflective Perspective - Chris Alcock » The Morning Brew #55 Says:

    […] 13 Tips to Comment Your Code – Some excellent advice about commenting, translated from an original article in Spanish. […]

  9. hosting reviews Says:

    Great article, it’s good to know how to comment your code, especially for large projects…

  10. Ngu Soon Hui Says:

    An insightful article! I’ve written a response:

  11. Denny Ferrassoli Says:

    I have a habit of removing the word “the” in my comments. They seem useless to me.

    Like your example above:
    “As soon as a line of code is laid on the screen, you’re in maintenance mode on that piece of code.”

    “As soon as a line of code is laid on screen, you’re in maintenance mode on that piece of code.”

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  15. sunfly Says:

    Good Job!
    I have translated it with Chinese.
    But,I have a question.
    “There is no point in commenting correctly on code ”
    I donot know its meaning.I cann’t translate it.Would you explain it ? Thanks.

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  19. Lee Says:

    (a) say what the code is INTENDED to do, not what it literally does,
    (b) make it so that you could understand how the program works if you lost all the code and only had the comments to work from,
    (c) make all comments non-technical – e.g. don’t waste time referring to variables by name,
    (d) comment everything, or at least use TODO when prototyping to allow you to come back and fill in all your missing comments later

  20. Peter Oakleaf Says:

    I like it! Kind regards/ PeTter

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  22. developer tips Says:

    “9. Comment code while writing it”

    This is the most useful tip in my opinion. If you write comments afterwards you may have a hard time remembering why you coded it the way you did (even if its the right way).

  23. wiiplayer12 Says:

    Real programmers don’t comment, if the code was hard to write, it should be hard to read!

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  33. limon Says:

    This is very interesting and very useful for beginners as well.

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  36. Deranged Carrot Says:

    Good post =D

    Definitely a Coding 101 that most people overlook. Even I’m guilty of it… it took my first big project to learn how blowing off documentation is a recipe for disaster…and block-box coding.

    Comments before code saves me hours if not days. Because after I finish one section sometimes I’m so into the previous section that I forget what the intentions of the previous codeblock where =P

  37. The Real Reason to Comment Your Code Says:

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  39. Pico RG Says:

    I don’t like scripts that are commenting much since I found out that they are too slow

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  42. Mark Says:

    In response to all those who say things like ;

    “Or, better yet, don’t do comments and make the code speak for itself”

    What a load of garbage. !! For professional companies and programmers, comments are a must. Code needs to be maintained and the original developer is not going to be there forever, and if they are, they probably won’t remember what the heck they wrote a function or class for anyway two years down the track.

    As an employer, or company CIO, or owner of a piece of code that needs to be updated / maintained, the last thing you want is to have a new developer sitting crawling through code unnecessarily trying to read and interpret someone else’s style and determine what a piece of code is doing, when all they needed to do was read the Brief, and the Date it was done, and any Updates that were added and Why.

    Laziness is no excuse to not be professional and think about those coming along behind you that may need to review what you have done. A simple few lines of comment could save a great deal of time, money, and grief.

  43. Anders Lindén Says:

    Mostly, the urge to write a comment serves as an indicator that your code needs to be improved.

    How the code in tip 2 could be made comment free:

    And the code in tip 3:
    const MAX_NUMBER_OF_PACKETS = 10;
    const TCP_BITMASK = 0x1F;

  44. Xo66uT Says:

    Good article, but what about using phpDocumentor and others for other languages ?

  45. Maurice Says:

    An interesting article. I have written an article about Code Commenting in Context which might be of interest to your readers

  46. dhaval Says:


  47. kk Says:

    Awesome article, I love commenting code and I yet need to further refine that skill.

    But for
    const MAX_ITEMS = 10; // maximum number of packets
    const MASK = 0x1F; // mask bit TCP

    I don’t think there’s a need to comment the meaning for the variable if we can just name it clearly..Why not call it a TCP_BIT_MASK 🙂

  48. Anders Lindén Says:

    kk, you are almost repeating in comment 47 what I was saying in comment 43

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    I don’t like scripts that are commenting much since I found out that they are too slow

  53. seo Says:

    so, I love commenting code and I yet need to further refine that skill.

  54. Anders Lindén Says:

    Scripts that are commented are running too slow?
    Did you really get a measureble difference?

    Scripts that are commented are slow… to read

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    Pay special attention to refactoring tools that automatically update code but leave comments unchanged and hence obsolete in the same instant.

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  58. Costa Del Mar Harpoon Says:

    What I hate is people who try to code their own job security into their work.
    They never want anybody else to understand it!

  59. Robert Walker Says:

    Another tip: when you need to fix a bug, also fix any existing comments if any of them are unclear or misleading. Also take the opportunity to add more comments to explain things better if you found any of the code hard to understand while tracing the bug, of course make sure you do understand the code before commenting it.

  60. Anders Says:

    Show me a snippet of well commented code and I can make it a lot clearer/understandable without comments. Dont forget to do this!

  61. Robert Walker Says:

    Also when the code uses published example code – e.g. examples from microsoft or codeproject, codeguru etc – add url to the original code as a comment. Similarly for ideas and concepts, add urls or references to the code comments. Even if it is easy to find it again, still adding the url makes it quick to maintain the code in the future, if you need to go back to the source, and only takes a moment or two – general guide if you needed to search for something on google to do the coding, chances are it is worth putting the url into the code comment.

  62. px9o Says:

    Great article, it’s good to know how to comment your code, especially for large projects…What I hate is people who try to code their own job security into their work.
    They never want anybody else to understand it!

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  66. Although Says:

    Finally! While we can agree that being a powerful speaker is all well and good, but at some point you have to “get something done”.

  67. Mr. F M Says:


    I am working with software firm and here I am working with one of oldest project and I found too much comments and among then there many comment are unnessary so my question is.

    Is unnessary comment can reduce performance or create any problem in existing application?

    Can anyone please help me on same ?

    Thanks in Advance…

  68. Timm Says:

    @Mr. F M: Comments are processed at compile time and do not affect program performance.

  69. Code Commenting: Just How Important is it? | SAikins Designs Says:

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