I have the impression that a disproportional large fraction of overleaf users don't notice error messages, a typical comment stream often goes like:

Question: Why is the image placed incorrectly?

me: Can you add a MWE

OP: sure, here is the overleaf link: ...

me: Your example code does not compile and results in error messages about Undefined control sequence. You need to define \foo

OP: My code does not have errors. Look at the overleaf link, it compiles fine

me: Just because overleaf is exceptionally good at hiding error messages, does not mean that there are no error messages ...

The above dialogue is fictional, but many of you have probably experienced similar situations.

I think there might be some possibilities to tweak their UI to make users more aware of error messages (maybe some dialogue message "there are errors - go back to editor to fix or ignore and show pdf", just a quick idea off the top of my head).

Now it probably won't make much impression on overleaf if a none customer like me writes them "I have the impression your users are unaware of errors", but if there would be a list of questions which demonstrates this problem, maybe the impact would be higher. Unfortunately it is hard to search for this on the main site, because this problem is often discussed in comments and the questions are (correctly) not tagged with overleaf, because the tex problem is unrelated to the platform used.

Please help me to compile a list of questions, which were caused or made more complicate to solve because the OP did not notice error messages on overleaf

(my plan would be to collect examples over the next month or so and depending a bit on how many are found until then, write to overleaf)

I know that also many users of editors like texstudio ignore error messages, but I have the impression that most of them are aware that there are some red messages highlighted at the bottom left, they just argue that "the pdf looks fine" and ignore them anyway, which is equally bad, but another problem.

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    Do that many users really not notice a red box with a white cross in it next to the offending line that shows an error message when the mouse hovers over it and also a red box with the number of errors displayed over the log button (next to the recompile button)? – Nicola Talbot Nov 6 '18 at 14:17
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    @NicolaTalbot I have this impression, yes. If I'm wrong and not many example will be added to the list below, I'll stand corrected. – samcarter_is_at_topanswers.xyz Nov 6 '18 at 14:19
  • If the problem comes up again, I've added an answer that could be referenced to show how to spot the errors if that helps. – Nicola Talbot Nov 6 '18 at 14:40
  • @NicolaTalbot Thanks a lot, this will surly be helpful in the future! – samcarter_is_at_topanswers.xyz Nov 6 '18 at 14:41
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    @NicolaTalbot I am absolutely sure that this happens because I experienced it myself, and not just once. – user121799 Nov 6 '18 at 18:25
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    @marmot It's certainly not as obvious as it used to be before the merger with ShareLaTeX. – Nicola Talbot Nov 6 '18 at 18:44
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    @NicolaTalbot Could very well be. I just wanted to express that I had a few conversations of the type: "Your code throws errors". "What are you talking about, it compiles just fine!". – user121799 Nov 6 '18 at 19:00
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    OTOH, the homepage currently has tex.stackexchange.com/q/458711/107497 where the Overleaf user just posted images of their error messages instead of the code that caused the error messages. – Teepeemm Nov 6 '18 at 22:13
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    People are ignoring error messages in all editors and GUIs, not just Overleaf. I don't think it is our responsibility here to make changes there. Write them a mail raising your concerns. I once wrote them a mail and got a response by one of the founding members 10 minutes later, and it was a sunday evening. – Johannes_B Nov 7 '18 at 6:21
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    I consider myself a rather experienced TeX user by now but I fell into this exact problem. I missed the error messages in OverLeaf. I think the reason is that when doing LaTeX what is interesting is the pdf file. IF the pdf file looks right what do I care if there is a long list of error messages? However as I experienced it is impossible to get help with things that doesn't even compile... – jonalv Nov 7 '18 at 8:53
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    (I'm a co-founder at Overleaf.) Just a note to say this question generated quite a lot of discussion internally! Overleaf v1 refused to produce a new PDF if there was any error; v2 uses the ShareLaTeX behaviour of always producing a PDF where possible. Both approaches have pros and cons. We are planning to review how we present the errors in v2 to see if we can make it less likely that people will ignore them. (We don't have a definite timeline on this yet, but we will see what we can do.) Thanks for all the feedback in this thread, and especially to Nicola for the very comprehensive answer! – jdleesmiller Nov 7 '18 at 11:11
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    @jdleesmiller Thanks a lot for your comment! Making Overleaf aware of this was much easier than I thought :) – samcarter_is_at_topanswers.xyz Nov 7 '18 at 13:10
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    @jdleesmiller I've taught beginners starting with Overleaf in class and, even when I've showed them where to look, they still find it hard to notice the error exists or to figure out where the error is. It is also tricky that the standard advice to 'delete the .aux file', say, isn't obviously related to 'recompile from scratch', which is itself hidden in a box only seen when there's an error. (If you want to force compilation for some other reason, is there any way other than deliberately causing a compilation error?) – cfr Nov 14 '18 at 3:00
  • @jdleesmiller And that was before the merger .... – cfr Nov 14 '18 at 3:01

Overleaf and ShareLaTeX recently merged into Overleaf v2. Before the merger, errors on Overleaf looked like this:¹

image of Overleaf showing errors

There's a big red rectangle with the error message over the problematic line.

Errors on ShareLaTeX looked like this:²

image of ShareLaTeX showing errors

This shows a red box with a white cross in it next to the line number. The error message shows as a tooltip. The right panel shows more detail.

Since the merger, Overleaf v2 has adopted the ShareLaTeX approach of showing a red box with a cross in it next to the problematic line with the mouseover message, shown below:

image of error showing in Overleaf v2

Moving the mouse over the red box shows the error message. The "logs and output files" button has a red box with the number of errors in it (1 in this case). Click on that button to show more details.

Warnings show up as a yellow triangle with an exclamation mark inside it and the number of warnings shows up in an orange box over the "logs and output files" button.

image of Overleaf document with warnings

Where there are both warnings and errors, the total number is shown in a red box over the "logs and output files" button.

image of Overleaf document with error and warnings

If you click on the "logs and output files" button then a summary of the errors and warnings is displayed.

image of Overleaf document with log summary

So the new v2 interface has the more discreet ShareLaTeX style of alerting users to a problem, but if you do notice the little numbered box over the "logs and output files" button and click on it, then it does actually provide some useful information for a beginner who may find the usual LaTeX messages a bit baffling.

¹Image taken from Figure 13.8: Overleaf — Error Handling.

²Image taken from Figure 13.9: ShareLaTeX — Error Handling.

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  • moreover I believe that (a) v1 would treat, for example, undefined control sequence as a fatal error, and everything would stop but (b) v2, flags it but keeps going when it can. I've already complained to Overleaf that v2 is too permissive. – Jim Ratliff Nov 10 '18 at 17:26

List of questions, which were caused or made more complicate to solve because the OP did not notice error messages on overleaf:

Overleaf users which are aware of error messages but ignore them:

Overleaf users not getting an error while there is an error on standard LaTeX installations:

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    I like this list! Thanks! I will add future instances here, now I cannot remember where I saw these things happening, but I am absolutely sure that they did happen. – user121799 Nov 6 '18 at 18:30
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    @marmot Thanks for keeping an eye open for this! It is very unfortunate that it seems nearly impossible to search for such conversations, so I think as many users as possible keeping an eye open is the only possible way to find them. – samcarter_is_at_topanswers.xyz Nov 6 '18 at 19:56
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    @jonalv Thanks a lot for sharing your answer! – samcarter_is_at_topanswers.xyz Nov 7 '18 at 9:27
  • @samcarter: What would help here is to recreate each of the posts as an OverLeaf project that one can visit in order to replicate it. – Werner Dec 4 '18 at 16:27
  • @Werner I not an overleaf user myself, but if any overleaf user would like to recreate the example, please feel free to edit the answer – samcarter_is_at_topanswers.xyz Dec 6 '18 at 22:53

Not only questions but also answers.

Here both Dũng Vũ and I didn't notice the error: Put additional features for elementary row operations in latex.

Overleaf shows this:

enter image description here

Only if you click on "Logs and output files" and then on "View Raw Logs" you'll see it:

enter image description here

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    That shows quite nicely that it can be dangerous to rely on editor's parsing of the .log file. Apparently Overleaf catches LaTeX Warning: and Package <pkg> Warning:, but fails to catch LaTeX Font Warning... You should probably send them a quick mail... – moewe Dec 4 '18 at 16:09
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    Would it be possible to create an OverLeaf project that replicates this issue? The one int he linked post is not available publicly. The reason I'm asking is because the .log doesn't show any errors in the image, only warnings. So it - OverLeaf - doesn't seem like it's doing anything wrong. – Werner Dec 4 '18 at 16:24
  • @Werner Indeed it's only a warning. But shouldn't it be shown? To replicate the issue just copy and paste Dung Vu answer (I'm not at home at the moment). – CarLaTeX Dec 4 '18 at 17:56
  • @CarLaTeX: To be pedantic, this question is about errors, not warnings. – Werner Dec 4 '18 at 17:59
  • @Werner Errors are shown is red, warnings in orange, but they should have been shown. It's an error by Overleaf, I think it's analogous in this case. – CarLaTeX Dec 4 '18 at 18:28
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    @moewe Done, I'll let you know what they reply. – CarLaTeX Dec 4 '18 at 19:53
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    @Werner See here: v2.overleaf.com/read/pvtfkgybkngk the overfull hbox is shown, if you click on "Logs and output files", but the "LaTeX Font Warning: Command \scriptsize invalid in math mode on input line 5." is not. – CarLaTeX Dec 4 '18 at 19:57

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