Current output looks like this:

error parsing JSON in the config file ~/config_invalid.json:
The file contains invalid JSON syntax: invalid character 'e' in string escape code

Here's an example output of how it would look if we were to highlight the syntax error

error parsing JSON in the config file ~/config_invalid.json:
The file contains invalid JSON syntax at ':"D:\\Users\e' <~
invalid character 'e' in string escape code

Thoughts? Not sure if it adds any more value.

Would it be possible to add full path to the config and number of line causing the error?

Each bit more of info you can supply to folks always helps, I say. :]

Would it be possible to add full path to the config and number of line causing the error?

@mtakac The full path will be displayed, I changed it for the example but it will look like

error parsing JSON in the config file /var/folders/_2/0wpr12717gg2g8btfc3fvr4w0000gn/T/485490851/config_invalid.json

Adding the line number should be trivial but the issue is that the config file is usually just 1 line unless the user modifies it to be pretty.

Each bit more of info you can supply to folks always helps, I say. :]

Definitely! Though I wanted to get feedback in case too much info can be overwhelming for the user but I guess it couldn't hurt in this scenario since they're already running into an issue.

👍 looks great and clear.

The latest commit makes the error output:

2015/04/02 19:42:21 error parsing JSON in the config file /Users/tonkpils/.exercism.json:
The file contains invalid JSON syntax at 'm.io", "foo"}' <~
invalid character '}' after object key

We could also write the config file pretty--it's not costly for such a small file, and if it would make it easier to give good error messages, that's a plus.

@kytrinyx sure, do you want me to get that in with this PR or in a different one?

pretty can happen in a separate PR, I was just thinking out loud :)

Thanks @Tonkpils!