This page takes text entered into the box above and adds a "zero-width space" after each period (.) character. Adding the zero-width space does not change the appearance of the text, but it causes Twitter to ignore the period and not construct any URLs from the text. Note that this process increases the character count by one per period.
If you which to add a URL, simply insert the URL once the text has been pasted into Twitter.
Use the "Copy" button to copy the updated text for pasting into Twitter. Using any other method to copy the text from the textbox will not insert the zero-width spaces as desired.