Widgets are rich, multi-featured mobile applications that are easy to create, fast to deploy, and run instantly across a wide selection of devices. Developers and publishers use Widgets to mobilize their content and services for their own customers, as well as gain instant reach to Yahoo!’s millions of mobile users.

Mobile Widgets allow you to get any content or service you desire into potentially millions of consumers hands on every device that Yahoo! supports. It's never been this easy to get so much coverage with such relatively little effort. Down the road, Mobile Widgets will be even more powerful as they start to run directly on the devices, giving access to all of the more interesting features our devices have today.

The Blueprint SDK has the information you seek. You can also get an overview here.

Users can find and get Widgets through Yahoo! Go 3.0 and Yahoo!’s new mobile homepage. Any user can simply visit the Widget Gallery via the gears icon in Go 3.0 or the Yahoo! mobile homepage to find and save your Widget. To distribute your Widget to Yahoo’s large mobile audience, submit it to the Widget Gallery here

We are constantly working to increase the number of supported devices for Yahoo! Go 3.0. You can always find the latest list of supported devices here

We do not charge any fees to use the Yahoo! Mobile Developer Platform.

You can always find the latest, constantly updated collection of Mobile Widgets in the Widget Gallery.

We chose simple XML over Java or AJAX for several reasons:

• It’s easy. We provide much of the layout and formatting. You just provide your content.
• No scripting. Many of the devices Yahoo! supports don’t have any scripting ability. We need to be able to still deliver content in those environments.
• It simply provides us with the widest possible array of devices on which to run by allowing us to control the implementation.

In subsequent releases, there will be more flexibility as devices get more powerful.

You can put whatever content your heart desires in your Widget. However, we do have some guidelines around Widgets we will not accept in the Yahoo! Mobile Widget Gallery:

• No illegal or prohibited content. Use of the Yahoo! Mobile Widget Gallery must comply with all applicable local, state, and federal rules, regulations, and laws. Don’t upload content that is illegal or prohibited. This includes content protected by any intellectual property rights, including but not limited to copyright, trademark, or other proprietary rights, without permission from the owner. If we find you doing that, your account will be deleted and we'll take appropriate action, which may include reporting you to the authorities.
• No inappropriate content. Because the Yahoo! Mobile Widget Gallery is open to people of all ages, Widgets containing sexually explicit or vulgar language or images are not welcome. Violent, racist, or incendiary content are similarly not allowed. If you’re not sure whether you’re crossing the line, we encourage you to solicit opinions in the Yahoo! Mobile Developer Group. We’ll reject or remove any Widget we find to be inappropriate, and repeat offenders may have their accounts deleted.
• No harmful content. Using a Widget for fraudulent or malicious purposes in any way is prohibited. This includes, but is not limited to, phishing, invasion of privacy, installation of malware or spyware, and any other unauthorized activity on a user’s computer. If we find you doing that, we'll delete your account and take appropriate action, which may include reporting you to the authorities.

Sure, go for it. We don’t support it directly at present, but in the future there will be a simple way to drop in an ad into your Mobile Widget using any ad service you prefer.

We will be adding tracking and reporting features into the platform in future releases—watch this space.

Our Yahoo! Mobile Developer Group may help you find the answers.

Yahoo! Groups : Yahoo! Mobile Developers