Inputting erroneous input such as https://www.google.co.uk/ returns a 404 with no description.
Although this isn't a specific use case I had copied a pasted a number of the format
And this also returned the same page.
Thanks for the report.
It looks as if URI::encode does not percent-encode / to %2F. We'll need a more robust escaping/encoding solution in lib/sundial.rb. I'll fix this later on.
Fixed on master in 4ea7384.
The fix has been deployed to (my live hosted copy)[http://sundial.benjaminasmith.com], too.