Percent encoding is the term for when a browser or other application changes characters from a URL into a three-character series starting with a percent symbol. This often happens with punctuation — for example, an exclamation point (!) may be replaced by %21.
When shortening a URL in Bitly, you may submit a URL that is percent encoded. We normalize most percent-encoded characters, changing them back to the original. For example:
Submitted URL
http://bitly.com/test?param=http%3A%2F%2Fdomain.com
Normalized URL
http://bitly.com/test?param=http://domain.com
The normalized version is the one you would see in your Links page. It looks different than the percent-encoded version, but they're the same thing.
When using the Bitly API, issues may arise if your server expects a percent-encoded URL. We won't return. In these cases, we recommend setting up your integration up to work with normalized URLs.