Looks cool. I corrected some of your spelling and grammar errors. Many US customers distrust sites that have poor English in their copy. Hope it helps.

ID and Password

We don't store your Dropbox and Google Drive passwords. (We cannot access this information.)

We store your OAuth token for Dropbox and Google Drive in our server.

We store a cookie in your browser.

We store your e-mail address for Dropbox and Google Drive in our server. This is for you to identify what account you use on Writebox.

File Contents

We don't store your file contents in our server, but save in your local cache.

We don't read your file contents, we just convert file encoding to show characters correctly.

We store the filepath of the thing you last opened in Writebox in our server. This is for syncing the last edit of the file across devices.

Logging

We collect analytics data through Google Analytics when you using Writebox. This is for the purpose of service improvement.

We don't track individual users.