GMail has this feature where it will warn you if you try to send an email that it thinks might have an attachment.

Did you mean to attach files?

Because GMail detected the string see the attached in the email, but no actual attachment, it warns me with an OK / Cancel dialog when I click the Send button.

We have a related problem on Stack Overflow. That is, when a user enters a post like this one:

my problem is I need to change the database but I don't won't to create 
a new connection. example:

DataSet dsMasterInfo = new DataSet();
Database db = DatabaseFactory.CreateDatabase("ConnectionString");
DbCommand dbCommand = db.GetStoredProcCommand("uspGetMasterName");

This user did not format their code as code!

That is, they didn't indent by 4 spaces per Markdown, or use the code button (or the keyboard shortcut ctrl+k) which does that for them.

Thus, our system is accepting a lot of edits where people have to go in and manually format code for people that are somehow unable to figure this out. This leads to a lot of bellyaching. We've improved the editor help several times, but short of driving over to the user's house and pressing the correct buttons on their keyboard for them, we're at a loss to see what to do next.

That's why we are considering a Google GMail style warning:

Did you mean to post code?

You wrote stuff that we think looks like code, but you didn't format it as code by indenting 4 spaces, using the toolbar code button or the ctrl+k code formatting command.

However, presenting this warning requires us to detect the presence of what we think is unformatted code in a question. What is a simple, semi-reliable way of doing this?

  • Per Markdown, code is always indented by 4 spaces or within backticks, so anything correctly formatted can be discarded from the check immediately.
  • This is only a warning and it will only apply to low-reputation users asking their first questions (or providing their first answers), so some false positives are OK, so long as they are about 5% or less.
  • Questions on Stack Overflow can be in any language, though we can realistically limit our check to, say, the "big ten" languages. Per the tags page that would be C#, Java, PHP, JavaScript, Objective-C, C, C++, Python, Ruby.
  • Use the Stack Overflow creative commons data dump to audit your potential solution (or just pick a few questions in the top 10 tags on Stack Overflow) and see how it does.
  • Pseudocode is fine, but we use c# if you want to be extra friendly.
  • The simpler the better (so long as it works). KISS! If your solution requires us to attempt to compile posts in 10 different compilers, or an army of people to manually train a bayesian inference engine, that's ... not exactly what we had in mind.
  • 34
    I think if you just always display the warning if there is no indentation present, you will be way below the 5% error limit. This is only half meant as a joke. Commented Jun 28, 2011 at 8:47
  • 59
    @Konrad This would work even better if the message would be: 'Either your question is missing code samples that would help others to understand it or you forgot to indent them properly'. This should cover 99% of all cases. Commented Jun 28, 2011 at 9:09
  • 3
    This is a GOOD question but I feel it doesn't have an answer. You show me an idiot-proof system and I will show you a better idiot. Even if this problem could be addressed by CODE, perhaps it shouldn't? It is these ignorant people who can't be bothered to ask a PROPER QUESTION that are RUINING this site for people like me who ask proper questions AND contribute proper answers IMHO.
    – maple_shaft
    Commented Jun 28, 2011 at 11:26
  • 2
    A common pattern I've seen is a block of code that was properly indented in itself, but where the first and last lines (usually only those two, sometimes more when showing multiple functions, for example) aren't labeled as code. This probably should be detected too.
    – 3Doubloons
    Commented Jun 28, 2011 at 15:09
  • 3
    On a side note, the GMail confirmation text is rather confusing. If your answer on the first question is 'yes' then the answer on the second question is 'no'...
    – pimvdb
    Commented Jun 28, 2011 at 15:55

14 Answers 14


A proper solution would probably be some learned/statistical model, but here are some fun ideas:

  1. Semi-colons at the end of a line. This alone would catch a whole bunch of languages.
  2. Parentheses directly following text with no space to separate it: myFunc()
  3. A dot or arrow between two words: foo.bar = ptr->val
  4. Presence of curly braces, brackets: while (true) { bar[i]; }
  5. Presence of "comment" syntax (/*, //, etc): /* multi-line comment */
  6. Uncommon characters/operators: +, *, &, &&, |, ||, <, >, ==, !=, >=, <=, >>, <<, ::, __
  7. Run your syntax highlighter on the text. If it ends up highlighting some high percentage of it, it's probably code.
  8. camelCase text in the post.
  9. nested parentheses, braces, and/or brackets.

One could keep track of the number of times each of these appears, and these could be used as features in a machine-learning algorithm like perceptron, the way SpamAssassin does.

  • 25
    Tips: 3 has a very low weight, because a dot between words can be the result of a typo. 5 should not match URLs. For 6 the ampersand is also frequently used outside the code context this you might also weight that character less. Double check if the highlighter works, because it can highlight non-code text as I sometimes see in Notepad++. Commented Jun 28, 2011 at 10:27
  • 8
    re the . as a typo - there would be no harm in flagging that as the author ought to edit anyway.
    – mmmmmm
    Commented Jun 28, 2011 at 10:29
  • 4
    additionally, specific keywords that many languages have could help: WHILE, ELSE, IF, LOOP, BREAK, etc. Commented Jun 28, 2011 at 10:45
  • 6
    Add "Usage of $ before non numeric words: $var is common in Perl and PHP (and Ruby?)."
    – PhiLho
    Commented Jun 28, 2011 at 11:37
  • 4
    You won't detect my SELECT DISTINCT name FROM people WHERE id IS NOT NULL.
    – Benoit
    Commented Jun 29, 2011 at 4:57

I would be curious to see what are the average metrics of written English on one side, and code on the other side.

  • length of paragraphs
  • length of lines
  • size of words
  • chars used
  • ratio between alphabetic, numeric and other symbol characters
  • number of symbols per word
  • etc.

Maybe that alone could discriminate already between code and the rest. At least I believe code, regardless of language, would show some noticeably different metrics in many cases.

The good news is: you already have plenty of data to build your statistics upon.

Ok I'm back with some data to back my assumptions up. :-)

I did a quick and dirty test on your own post and on the first post I found on StackOverflow, with a pretty advanced tool: wc.

Here is what I had after running wc on the text part and on the code part of those two examples:

First lets look at the English part:

  • The English part of your post (2635 chars, 468 words, 32 lines)
    • 5 chars/word, 82 chars/line, 14 words/line
  • The English part of the other post (1499 chars, 237 words, 12 lines)
    • 6 chars/word, 124 chars/line, 19 words/line

Pretty similar don't you think?

Now lets take a look at the code part!

  • The code part of your post (174 chars, 13 words, 3 lines)
    • 13 chars/word, 58 chars/line, 4 words/line
  • The code part of the other post (4181 chars, 287 words, 151 lines)
    • 14 chars/word, 27 chars/line, 2 words/line

See how not so different those metrics are, but more importantly, how different they are from the English metrics? And this is just using a limited tool. I am now sure you can get something really accurate by measuring more metrics (I'm thinking in particular of chars statistics).

I can haz cookie?

  • 6
    Line length, particularly if you exclude bullet points and look for clustered lines of less than a particular length containing specific punctuation would seem to be a good measure. Commented Jun 28, 2011 at 9:30
  • This would work for blocks of code, but it'd seem a whole lot harder to look for inline cdde. Not sure how much that matters, though -- the bigger problem is big blocks of unformatted code anyway.
    – cHao
    Commented Jul 2, 2011 at 17:42
  • 3
    No cookies. The link in your post is 404. Commented Oct 3, 2014 at 12:21
  • @james.garriss: the Internet stole my cookie jar. :( Thank you for the notice though. Commented Oct 8, 2014 at 14:27

Typically, Markov chains are used to generate text, but they can also be used to predict the similarity of text (per C.E. Shannon 1950) to a trained model. I recommend multiple Markov chains.

For each prevalent language, train a Markov chain on a large, representative sample of code in the language. Then, for a Stack Overflow post for which you want to detect code, do the following for each of the chains:

  • Loop through the lines in the post.
    • Declare two variables: ACTUAL=1.0 and HIGHEST=1.0
    • Loop through each character in the line.
      • For each character, find the probability in the Markov chain that the current character is the one following the previous N characters. Set ACTUAL = ACTUAL * PROB1. If the current character is not present in the chain, then use a tiny value for PROB1, like 0.000001.
      • Now, find the character most likely (i.e. the highest probability) to follow the previous N characters. Set HIGHEST = HIGHEST * PROB2.
      • Obviously, PROB2 >= PROB1

For each line, you should have an ACTUAL and a HIGHEST value. Divide ACTUAL by HIGHEST. That will give you the fitness score as to whether a particular line is source code. That would associate a number with each of the lines in the example you gave:

my problem is I need to change the database but I don't won't to create // 0.0032
a new connection. example: // 0.0023

DataSet dsMasterInfo = new DataSet(); // 0.04
Database db = DatabaseFactory.CreateDatabase("ConnectionString");   // 0.05
DbCommand dbCommand = db.GetStoredProcCommand("uspGetMasterName");  // 0.04

Finally, you'll need to select a threshold to determine when there is code in the post. This could simply be a number selected by observation that yields high performance. It could also take into account the number of lines with a high score.


To train, procure a large, representative sample of code in the language. Write a program to loop over the code text and associate each N-gram in the file (the range for N should be parameterized) with the statistical frequency of the subsequent character. This will yield multiple possible states of characters that follow the bigram, each associated with a probability. For example, the bigram "()" could have some following character probabilities of:

"()" 0.5-> ";"
"()" 0.2-> "."
"()" 0.3-> "{"

The first should be read, for example as "The probability that a semicolon follows an empty parenthetical is 0.5."

For training, I recommend N-grams of size two through five. Back when I did some research on this, we found that N-grams size two through five worked well for English. Since much of source code is English like, I'd suggest starting with that range and then adjusting to find the optimal parameter values as you find what works.

A caveat: The model is going to be affected by identifiers, method names, whitespace, and etc. However, you can tune the training to omit certain features of the training sample. For example, you could collapse all unnecessary whitespace. The presence of whitespace in the input (the Stack Overflow post) can be ignored as well. You could also ignore alphabetical case, which would be more resilient in the face of varying identifier naming conventions.

During my research, we found that our methods worked well for Spanish as well as English. I don't see why this wouldn't also work well for source code. Source code is even more structured and predictable than human language.

  • 2
    The only problem I foresee is that the probabilities will be vastly smaller than in your toy example. Given numerical instability, this means that soon all probabilities are 0. Using log odds solves this though. Furthermore, I’d use larger tokens (i.e. not characters but words/punctuation). Commented Jun 28, 2011 at 15:20
  • 2
    @Konrad: the idea here isn't to test absolute probabilities: it's to test relative probabilities. For each line, is the text of that line more likely to have been generated by an English language model, or by a code language model.
    – Ken Bloom
    Commented Jun 28, 2011 at 15:48
  • 5
    You can train this model on existing SO posts (particularly because you may need to account for Markdown syntax). If you assume that most posts are formatted correctly (or you pick through a large number of posts, on the order of tens of thousands, to remove posts that are not formatted correctly), then you assume that stuff that's not code formatted is English text, and stuff that is code formatted is code, you can train from actual SO answers.
    – Ken Bloom
    Commented Jun 28, 2011 at 15:51
  • 1
    A tutorial about how to do this (using LingPipe in Java) is available from LingPipe's website. At the end of the tutorial, there are a number of papers on techniques to tackle this problem. I suggest reading them.
    – Ken Bloom
    Commented Jun 28, 2011 at 16:04
  • 1
    It’s interesting to see that the state of the art solution has only a very low vote count, and rates vastly less than all those ad-hoc solutions which, admittedly, might just be good enough but rely a lot on special-casing and are inherently prone to overfitting. Commented Jul 3, 2011 at 10:56

May I suggest a radically different approach? On SO the only human-language allowed is English, so anything that is non-English has 99.9% of chances to be a code snippet.

So my solution would be: use one of the many English language-checkers out there (just make sure they also signal - beside misspellings - syntax mistakes like double dots, or non-language symbols like # or ~). Then any line/paragraph that throws a large amount of errors and warnings should trigger the "is this code?" question.

This approach can also be adapted for those StackExchange sites using other languages than English, of course.

Just my 2¢...

  • 16
    The problem is that a lot of the incoming questions aren't English either (although they resemble it). Commented Jun 28, 2011 at 19:07
  • 3
    @Brendan - Added advantage of this proposal then: underline (or highlight) the mistakes in the probably-intended-to-be-English parts of the post and help the writer to write... in English! ;)
    – mac
    Commented Jun 28, 2011 at 19:12
  • 1
    I'm Dutch and everything I code is in English, by comments are not (depending on the project). So Non-English must be code would not suffice. That or you mean that broken English must be code.
    – Ivo Limmen
    Commented Jun 28, 2011 at 20:14
  • @Ivo - My comment was jokingly addressed to the broken English issue! ;) However I would say that with my proposal comments in another language would just work fine... OTOH block comments in English won't trigger the "is this code?" question, but that's just fine because the code for which the comment has been written would already have triggered it...
    – mac
    Commented Jun 28, 2011 at 20:22

I'm probably going to get a few down votes for this but I think you are approaching this from the wrong angle.

This line got me:

people have to go in and manually format code for people that are somehow unable to figure this out

IMO that standpoint is kind of arrogant. I find this a lot in software design where programmers and designers get annoyed with users who can't figure out how to use the software properly, when the problem isn't the user but the software itself - or the UI at least.

The root cause of this problem isn't the user but the fact that it isn't obvious to them that they can do this.

How about a change in UI to make this more obvious? Surely this will be:

  1. more obvious to new users exactly what they need to do
  2. easier for you to build rather than writing complex algorithms to detect code logic of a multitude of languages


enter image description here

  • 27
    Actually this IMO enforces poor questions like "I have a problem please help me, the code is below" - quite rarely code needs to be separated from the question. Best questions go like this "I want to achieve this and wrote these two lines of code, but the effect is the following, what's the problem" - there's very little code heavily interleaved with plain language.
    – sharptooth
    Commented Jun 28, 2011 at 12:50
  • 4
    Your root observation is correct but your diagnosis is still wrong: in fact, Jeff is trying to improve the user interface via this approach. Furthermore, the current UI has already gone through several cycles and while I don’t doubt that it could be improved (drastically), I doubt that this would help against lazy idiots. Neither would your proposed solution. @sharptooth has this covered. Commented Jun 28, 2011 at 15:24
  • 2
    I would +1 for thinking out the box but I disagree with the specific suggestion, since posting "supporting code" forces a question flow that may be unnatural. I have never just dumped in code at the bottom of my question. I almost always post an intro, the sample code, then the actual question. If you accept this premise that inline code is essential, then some type of formatting is required -- formatting which must be entered by the user or recommended by the system. And that's the exact thing that Jeff is asking about doing.
    – Nicole
    Commented Jun 28, 2011 at 16:23
  • 1
    @Konrad: In addition to my above comment and in response to yours, I don't believe the Jeff is improving the UI by taking this path, but merely treating the symptoms of an underlying problem. If the UI was improved so that the mistake couldn't be made, then the solution of alerting the user would not be necessary. I am under no illusion that my example is the final solution but some thought needs to go into the question "are we presenting this in the best way possible?". Commented Jun 28, 2011 at 20:29
  • 1
    The simple sentence please mark code using the {} button around the text box could be enough. Commented Jun 28, 2011 at 23:55

Pseudo code would pose a real challenge because all programming language depend on special characters like '[]', ';', '()', etc. Simply count the occurrence of these special characters. Just like you would detect a binary file (more than 5% of a sample contains byte value 0).

  • I would improve this as much as having groups of these special chars like [] () ; {} =. Each line that has more than 2-3 of these groups contained is a line of code.
    – Honza
    Commented Jun 28, 2011 at 8:19
  • ...and also look for common strings in the most common languages, e.g. " = someword();" for most curly bracket languages, XML-like syntax like "<something>" and "<ab:cde>", and other common strings in other languages. I do believe some sort of lookup table of common syntax would be a good solution, as you can expand it when you find new languages to implement. Commented Jun 28, 2011 at 8:27
  • You should probably drop pseudo code. Some people like to write it as a C-style language but other people will use plain english with something that looks closer to VB6
    – James P.
    Commented Jun 28, 2011 at 14:25

I think you may need to target this against only specific languages, in general this problem is likely intractable as you can get languages which are pretty similar to English (e.g. inform7). but luckily the most used ones could be covered fairly easily.

My first cut would be to look for the sequence ";\n" which would get you a good match for C,C++,Java, C# and any other language that uses similar syntax and is really simple. It is also less likely to be used in English than a ; without a newline

  • plus maybe an abundance of curly braces ;p Commented Jun 28, 2011 at 8:15
  • 1
    As Jeff says in his post, they would probably only target the main languages. And in any case, I suspect that new users (for whom this functionality is intended) will be more likely to post C# or Javascript than, say, INTERCAL ;-)
    – Ben
    Commented Jun 28, 2011 at 8:28
  • Yes but this would not work with the programming language BRAINFUCK or BLANK. ;-)
    – Ivo Limmen
    Commented Sep 3, 2012 at 18:01

Someone mentioned looking at the tags and then looking for syntax for that but that was shot down because this is aimed at new users.

A possible better solution would be to look for language names in the body of the question, then apply the same strategy. If I mention "Javascript", "Java" or "C#" then chances are that is what the question is about, and code in the question is likely to be in that language.

  • Especially if the title is something like "vb c# .net dot net help me help me!!!"
    – NickAldwin
    Commented Jun 28, 2011 at 14:12

First, run it through spell check, it will find very few proper English words, however there should be lot of words that spellchecker will suggest to split.

Then there are punctuation/special characters not typical for plain English, typical for code:

  • something(); just cannot be plain English;
  • $something where something is not all numeric;
  • -> between words w/o spaces;
  • . between words w/o space;

Of course to have it working well, you might want to have Bayesian classifier built on top of these characteristics.

  • 1
    Detecting a non indented line containing (); would be a good reason to suggest the message.
    – user2567
    Commented Jun 28, 2011 at 8:22
  • What spell checker won't choke prior to the code being pasted?
    – user131
    Commented Jun 28, 2011 at 9:09
  • With some messages written by non-native English writers, the spellchecker will choke on every other word...
    – PhiLho
    Commented Jun 28, 2011 at 11:33
  • @Ph: these question/answers are not accepted on SO anyway.
    – vartec
    Commented Jun 28, 2011 at 11:40

there are several sets of languages which share similar syntax. the most languages got influenced by a few languages, so the languages [AMPL, AWK, csh, C++, C-- , C#, Objective-C, BitC, D, Go, Java, JavaScript, Limbo, LPC, Perl, PHP, Pike, Processing[ were all influenced by C, so if you detect C you will probably detect all these languages. so you have only to write a simple pattern for detecting this language-sets.

i would also split the text into blocks because the most code will be split by two newlines or similar from the other text blocks in the post.

this can be easy done with javascript (a supersimple incomplete sample for the c family) :

var txt = "my problem is I need to change the database but I don't won't to create a new connection. example:\n\nDataSet dsMasterInfo = new DataSet();Database db = DatabaseFactory.CreateDatabase(&quot;ConnectionString&quot;);DbCommand dbCommand = db.GetStoredProcCommand(&quot;uspGetMasterName&quot;);";
var blocks = txt.split(/\n\n/gi); console.dir(blocks);
var i = blocks.length;
var cReg = /if\s*\(.+?\)|.*(?:int|char|string|short|long).*?=.+|while\s*\(.+?\)/gi;

while ( i-- ){
   var current = blocks[i];
   if ( cReg.test( current ) ){
      console.log("found code in block[" +  i + "]");

Simply count words / punctuation character for each line. English will tend to have 4 or more, code less than 2.

The paragraph above has 18 words, and 4 punctuation characters, for example. This paragraph has 19 words and 4 punctuation, so within expectations.

Of course, this would need to be tested against newbie poor-english speakers questions, and it may be that in those cases, the statistics are skewed.

I expect that [non-whitespace].[whitespace or newline] is very rare in code, but common in English, so this could be counted as words, not punctuation.

I think the biggest problem will be inline code, where someone asks a question like:

If I say for (i=0; i>100; i++) {} what does that mean?

That's code and English, and should be marked up as with back-ticks:

If I say for (i=0; i>100; i++) {} what does that mean?


I think you should first make a distinction between (sufficiently) formatted code that only needs to be actually designated as such, and (too) poorly formatted code, which needs manual formatting anyway.

Formatted code has breaklines and indentation. That is: if a line is preceded by a single breakline, you have a good candidate. If it has leading whitespaces on top of that, you have a very good candidate.

Normal text uses two breaklines or two spaces and a breakline for formatting, so there's a clear criterion for distinction.

In LISP code you will not find semicolons, in Ruby code you may not find parenthesis, in pseudo code you might not find much at all. But in any (non-esoteric) language you will find decent code to be formatted with breaklines and indentation. There's nothing as universal as that. Because in the end code is, written to be read by humans.

So first, search for potential lines of code. Also, lines of code usually come in groups. If you have one, there's a good chance that the one above or below is a line of code as well.

Once you have singled out potential lines of code, you can check them against quantifiable criteria and pick some threshold:

  • frequence of non-word characters
  • frequence of identifiers: very short words or very long words with CamelCase or under_score style
  • repetition of uncommon words

Also, now that there is programmers and cs, stackoverflow's scope is clearly narrowed down. One might consider denoting all language tags as languages. And when posting, you'd be asked to either pick at least one language tag, pick the language-agnostic tag or to explicitly omit it.

In the first case you know which languages to look for, in the second case, you might want to look for pseudo-code and in the last case, there probably won't be any code, because it's a question related to some technology or framework or such.


You could create a parser for each language you want to detect (language definitions for ANTLR are usually easy to find), then run each line of the question through each parser. If any line parses correctly, you probably have code.

The problem with this is that some english (natural language) sentences may parse as code, so you may want to include some of the other ideas as well, or you could limit positive results only if more than one or two consecutive lines parse correctly with the same language parser.

The other potential issue is that this will probably not pick up pseudocode, but that may be OK.

  • Often people have syntax errors in their code (and are asking about this). Commented Jun 29, 2011 at 0:02

What may be the most future-proof and require the least manual adjustment in the long run ,as other languages (which look somewhat different than the programming languages used most now) become more popular and the currently used languages become less popular, is to do something like what Google Translate does (see the paragraph titled "How does it work?"), instead of looking for certain things like a.b and a(), etc.

In other words, instead of manually thinking of patterns found in code to look for, the computer can figure it out by itself. This can be done by having

  1. lots of code in many different programming languages

    • Suggestion: automatically take code samples from web-based source code repositories like Google Code or Github, or even from things on Stackoverflow already marked as code

    • Note: it may be a good idea to parse out code comments

  2. lots of english text taken from articles on the web

    • although not from articles about programming (otherwise they may have code in them and mix the system up :-) )

and having some kind of algorithm automatically find patterns in the code that are not in the english, and vice versa, and using those patterns to detect what is code and what is not code by running the algorithm on posts.

(However, I am not sure how such an algorithm would work. Other answers to the current question may have useful information for that.)

Then the system can re-scan the code every once in a while to account for changes in the way code looks at that point in time.

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