I know this is more language problem, but in many applications there is a text "unexpected error occurred".

How do you get the sense (in context of UX) of this information? It makes me feel that the designer has prepared for me both expected and unexpected errors and I did something wrong and crashed the entire system, which was not even expected by its authors.

The similar is with "Unknown error occurred". Something went wrong, we don't even know what.

There are lots of posts here how an application should handle errors, should it show them to the user or hide (not only because of making a user feel losing control but also because of security reasons). I understand that in these cases the designer was "expecting an unexpected error" and maybe they ask me to report it, so they can fix the problem. This makes some sense with opensource software like Linux, Mozilla Firefox etc., which declare they are not error-proof and have dedicated bug-reporting websites or they do a memory dump and send it somewhere.

How should a (commercial, mostly) application handle "unexpected" or "unknown" errors (in case we decide to show errors to users)? Should they inform the user that not only a user has lost control, but a designer as well?

Does showing "unexpected" or "unknown" errors (or just "an error") mean that the UX is poorly designed?

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    I've always found "Unexpected error" redundant. If we were expecting the error, then we should have fixed it before shipping. :)
    – DA01
    Commented Aug 20, 2015 at 8:11

1 Answer 1


So there's actually some thought that's been put into error message. This article goes over the basic rules of error messages, which "unexpected error occurred" violates.

  • Be explicit. What is it that actually went wrong? If your developers are being lazy and letting the system simply say, "unexpected error," then it needs to be corrected.
  • Human readable. This means use plain language and don't get too technical.
  • Be polite. The user is already stressed by receiving an error, so there's no need to add to their anxiety.
  • Be precise. "Unexpected error" is extremely vague and doesn't guide the user towards the actual problem that occurred. How can they fix it if they don't know what it is?
  • Offer constructive advice. While the purpose of an error message is to explain that something went wrong, the goal should be to guide the user back to the right path. In a concise way, offer tips or links on how to correct the problem. Again, "unexpected error" does nothing to resolve the problem.

So the answer to your question is that commercial products and applications should never show an error that simply says, "unexpected error has occurred" because it violates basic error message guidelines. Once the content of an error message is properly written, then the most important thing is to make it easily visible and to have it stand out to the user.

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    As a developer I know about edge cases where we simply can't know what went wrong. We can neither be explicit here nor can we be precise and I would rather tell the user that something went wrong than to bore him with the assumption that a third-party plugin proably failed at some point. In theory your linked article sounds perfectly correct but it isn't always that easy. However not leaving the user alone and e.g. give him some feeling of control is always a good idea.
    – Marvin
    Commented Aug 20, 2015 at 16:10
  • 1
    The point about never showing an ambiguous error is to encourage best practices and to say you should be specific whenever systematically possible. Because you're right, sometimes you can't get good details from the system, but that doesn't mean you can't provide the user something better than, "Error 500."
    – tonytrucco
    Commented Aug 20, 2015 at 16:18
  • 1
    @Marvin I think your example actually counters your point- if you know it's some error in a plugin, that's exactly what you should say to the user "One of the plugins you installed/enabled has caused a problem. Please restart in Safe Mode ... etc."
    – J. Dimeo
    Commented Sep 15, 2016 at 3:07
  • Is any error "expected"? What does "unexpected" add?
    – JoelFan
    Commented Sep 13, 2018 at 18:51

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