How should an error message explain to users that they input the wrong URI scheme?

Question

On my site, users can add a link to a website. The validation checks if it has a scheme (e.g. http, ftp). If it has no scheme, it adds 'http'. But what if the user enters an ftp link, for example? I'm not sure how to explain to the user why their link is invalid.

I assume that a user who thought an ftp link was a website link has their hands on a few links associated with the project and just needs to identify the right one. I could tell them that they need to enter a link that starts with 'http', but they might not have been given the link with 'http' written in front of it.

So how can I help the user identify which link they should be inputting?

Answer 1

In a case user entered an URL starting from ftp:// and you really want to explain to the user why FTP protocol is wrong you may show her something like this:

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It will not only explain the problem briefly but also suggest a fix.

Answer 2

From your explanation, it seems that you are talking about a small specific set or URLs, so you should also check for the rest of the URL and transform the wrong one into a good that the user can use or copy.

So for instance, if the user enters ftp://www.example.com/ and you know that the www.example.com is correct, then you can print a text like the this "The web address that you entered seems to be incorrect, it should be written this way http://www.example.com/".

Provide a friendly text with the URL in a bit bigger font size so it's clear. You can also add a little text explaining that the problem was using FTP instead of HTTP. Don't make it too technical if that would confuse the users.

Of course you have to be sure that the URL you are providing as a response is correct, so I recommend testing it, you can use any tool that your environment allows you. I would recommend cURL. That way, if the URL has more problems, for instance a typo, you can tell that to the user.

Even better would be to tell the user what is the right URL is he made a mistake, but I don't know how feasible is that for you.