As the comments have pointed out, just because you didn't write any server side code, it doesn't mean it's not a web app. So, "web app" actually does fit, but may be a little too vague for your purposes, due to the lack of server side code with the app itself, though technically, if you hook into any APIs at all, then someone had to write server side code somewhere, even if that someone wasn't you.
"Web tool" and "web script" might be able to work, but they're really vague (in my opinion). Likewise, "standalone webapp" doesn't mean much, either. Standalone from what? Does that mean it can run without a browser? Any webapp could be considered "standalone," if you think about it. "Client-only"? Again, seems rather vague, especially if you're dealing with non-technical people, or anyone who doesn't understand the client-server nature of the web.