I'm gonna guess at the functionality of the program (since I cannot see the actual inner workings from here) and guess you're doing something relatively awesome with http headers? Curl was my friend from a little while ago, and 000webhost let's ya use it too...I hope.
Anyway, ranting over. Onto a cruel critique of what you have going for you so far:
- A small, snappy interface. Granted, it could be smaller (for more, take a look at the somewhat hard-to-find-documentation META VIEWPORT tag/attribute). While it probably looks great on a computer, web browsers on your phone will probably always scale it too big until then.
- Pretty much as simple as you can make it... for now. Your instructions are a bit loquacious and may work better in a numbered list.
- Lose the http:// start. Enter it within the textbox (for a user typing it in the URL) so if it's pasted over, you only have one http:// left over.
- Or make sure the string has no http://http:// at the front. that's probably easier.
- Something specific to GetJar pages. There's gotta be a formula for how to download an app; you should try figuring out what it is by looking at the source of some of the GJ pages/links.
- A list of last-loaded apps. Not a necessity, but will increase cool factor immensely.
My thumbs hurt now.