I have a mobile app with a new-data-object form where you enter an URL and some other (non-textual) settings. The most common way to enter the URL is to paste it from the address bar of the browser. (As it's a mobile app, you can also scan a barcode or an NFC tag, but both those options are less commonly available.) I'm trying to streamline this screen and make it easier to use.

I first thought of adding a Paste button similar to [this question](https://ux.stackexchange.com/questions/37641/will-a-paste-button-increase-usability), to remove the long-tap step from pasting, but then I thought I could remove even that step by looking at the clipboard contents when the form is entered and automatically pasting into the text box if the clipboard contains a (usable) URL.

This seems really streamlined, but I wonder if it might cause problems.

1. Not having a button makes it less discoverable (that you'd want to paste into the field). I can deal with this by having a message: if there wasn't a usable URL on the clipboard, display the message next to the text box to warn/inform the user that they could copy it from a browser. This would replace my existing message telling the user that the easiest way to enter the URL is to paste it.
2. It seems unlikely, but on occasion the user might have an unrelated URL on the clipboard, maybe even a sensitive one. But it's easy enough for them to delete it if that's not what they want.
3. It might be too "clever", or unexpected: the user was happily using a website, then suddenly the URL is in my app! Even if that's exactly what they intended, it's surprising in a *How did it know? What just happened?* kind of way.

Are there any other potential UX issues I should be aware of before adding this behaviour? I can fall-back to the idea of a button if there's a good reason not to do it automatically, but I'd rather not add that extra step unnecessarily.

I'm particularly looking for an answer based on direct experience or a reasoned theoretical basis, and/or supported by examples. "I think it's a good/bad idea," is the kind of thing I could have come up with on my own.