We don't have this spelled out on the site (yet), but here are some evolving guidelines:
Search Boxes Your app have a search box? Yup, so do we. Take care in where you place your search box so its not right next to or below one of ours.
Branding Plan to have application branding via a logo or image in the upper left corner. Strongly recommend use of your logo. Yahoo! logo may not be used.
Application Size Your apps primary canvas should be w/in a tab. With subsequent task such as a picker or alerts in an overlay. Note the default visible size to avoid horizontal or excessive vertical scrolling.
Tab Application Dimensions 675 x 595px [1024x768 screen resolution] Overlay Dimensions 620 x 500 px max, may be smaller 300x250px
Gallery Image Icon = 128x128 graphic A .png with a white background.
Application Name • App Name = up to 32 characters total. Note: 25 characters visible in folder pane. • No direct reference to Yahoo!/Yahoo! Mail.
Application Description • Up to 256 characters total • Provide a 300 x 250 px sample image • Include developer name and link to relevant information. • Description may indicate application was developed “especially for Yahoo! Mail” and should identify added value, i.e. photo sharing/management, organization, event planning , etc.