Action Details
Requirements and how-to articles for Xbox's action:

If your game integrates Xbox Live and follows Microsoft's standard Store policies, you are ready to publish with no concept approval required.

You need this to get it done:

The markets which your app will be offered in. By default this is set to all possible markets.
The audience section lets you specify whether you want to restrict the visibility of your submission to a specific audience that you define. By default this is set to public audience.
The selections in the discoverability section indicate how customers can discover and acquire your app. By default this is set to make this available and discoverable in the Store
The schedule section on the pricing and availability page lets you set the precise date and time that your app should become available in the Store, giving you greater flexibility and the ability to customise dates for different markets. By default this is set to release as soon as possible.
Base Price
When you select your app's base price, that price will be used in every market where your app is sold, unless you override the base price in any market(s). You can set the base price to free, or you can choose an available price tier, which sets the price in all the countries where you choose to distribute your app. Price tiers start at 0.99 USD, with additional tiers available at increasing increments (1.09 USD, 1.19 USD, and so on). The increments generally increase as the price gets higher.
Free Trial
Many developers choose to allow customers to try out their app for free using the trial functionality provided by the store. By default, No free trial is selected, and there will be no trial for your app. If you’d like to offer a trial, you can select a value from the free trial dropdown.
Sale Pricing (optional)
You can promote your app or add-on in the Microsoft Store by putting it on sale for a limited time. You can choose to offer the product either at a lower price tier or with a percentage-based discount, and you can choose whether to offer the sale to everyone, or make it an exclusive offer for customers who own one of your other products.
Organisational Licensing
You can indicate whether and how your app can be offered for volume purchases through Microsoft Store for Business and Microsoft Store for Education in the organisational licensing section of the pricing and availability page of an app submission. By default this is set to allow volume acquisition by organisations.
Category and Subcategory
Listing your app in the right category and subcategory helps customers find your app and understand more about it. You must choose the category that best describes your app. You can optionally choose a subcategory, if available. If you choose "Games" for your category, you are required to select at least one subcategory (called "genre" for games).
Privacy Policy URL
You are responsible for ensuring your app complies with privacy laws and regulations, and for providing a valid privacy policy URL here if required.
Website (optional)
Enter the URL of the web page for your app. This URL must point to a page on your own website, not your app's web listing in the Store. This field is optional, but recommended.
Support Contact Info
Required if your product is available on Xbox; otherwise optional (but recommended.) Enter the URL of the web page where your customers can go for support with your app, or an email address that customers can contact for support.
Game Settings (optional)
This section will only appear if you selected Games as your product’s category. Here you can specify which features your game supports. The information that you provide in this section will be displayed on the product’s Store listing.
Display Mode (optional)
This section lets you indicate whether your product is designed to run in an immersive (not a 2D) view for Windows Mixed Reality on PC and/or HoloLens devices.
Product Declarations
The product declarations section of the properties page of the submission process helps make sure your app is displayed appropriately and offered to the right set of customers, and helps them understand how they can use your app. By default this is set to customers can install this app to alternate drives or removable storage; Windows can include this app's data in automatic backups to OneDrive.
System Requirements (optional)
In this section, you have the option to indicate if certain hardware features are required or recommended to run and interact with your app properly.
Age Ratings
The age ratings page of the app submission process lets you provide information about your app so it can receive the appropriate age and content ratings administered by the International Age Ratings Coalition (IARC) rating system. These ratings are about the suitability of the content in the app, rather than the age of the target audience for your app.
Package Upload Control
The packages page is where you upload all of the package files (.msix, .msixupload, .msixbundle, .appx, .appxupload, and/or .appxbundle) for the app that you're submitting. You can upload all your packages for the same app on this page, and when a customer downloads your app, the store will automatically provide each customer with the package that works best for their device. At least one package is required.
Device Family Availability
After your packages have been successfully uploaded on the packages page, the device family availability section will display a table that indicates which packages will be offered to specific Windows 10 device families (and earlier OS versions, if applicable), in ranked order. This section also lets you choose whether or not to offer the submission to customers on specific Windows 10 device families. By default, this is based on your packages.
Gradual Package Rollout (optional, for updates only)
When you publish an update to a submission, you can choose to gradually roll out the updated packages to a percentage of your app’s customers on Windows 10 (including Xbox). This allows you to monitor feedback and analytic data for the specific packages to make sure you’re confident about the update before rolling it out more broadly. You can increase the percentage (or halt the update) any time without having to create a new submission.
Mandatory Update (optional, for updates only)
If your submission is an update to a previously published app, you'll see a checkbox that says "Make this update mandatory." This allows you to set the date and time for a mandatory update, assuming you have used the Windows.Services.Store APIs to allow your app to programmatically check for package updates and download and install the updated packages. Your app must target Windows 10, version 1607 or later in order to use this option.
A great description can make your app stand out in the Microsoft Store and help encourage customers to download it. The description you enter when submitting your app is displayed in your app's Store listing. The first few lines may also be displayed in search results and algorithm lists in the Store.
Here are Microsoft's tips for writing a good app description:
Grab attention in the first few sentences.
Make it easy to learn about your app.
Use lists and short paragraphs.
Avoid dry language.
Use a length that is just right (somewhere over 200 words, but well under 3000.)
Be clear about free trials and add-ons.
Use standard capitalisation and punctuation.
Don't forget to check the spelling and grammar.
Don't include links or info that belongs elsewhere.
Don't use HTML tags.
Get ideas by reviewing descriptions of similar apps in the Store.
What's New in This Version (optional)
If this is the first time you're submitting your app, leave this field blank. For an update to an existing app, this is where you can let customers know what's changed in the latest release. This field has a 1500 character limit.
App Features (optional)
These are short summaries of your app's key features. They are displayed to the customer as a bulleted list in the features section of your app's store listing, in addition to the description. Keep these brief, with just a few words (and no more than 200 characters) per feature. You may include up to 20 features.
Screenshots are images of your app that are displayed to your customers in your app's Store listing. You have the option to provide screenshots for the different device families that your app supports so that the appropriate screenshots will appear when a customer views your app's Store listing on that type of device. Only one screenshot (for any device family) is required for your submission, though you can provide several; up to 9 desktop screenshots and up to 8 screenshots for the other device families.
Poster Art
This is used as the main logo image for customers on Windows 10 and Xbox devices, so Microsoft strongly recommends providing this image to ensure proper display. This image should include your app’s name, and any text on the image should meet accessible readability requirements (4.51 contrast ratio).
File format: .png
Maximum file size: 50MB
Aspect ratio: 9:16
Dimensions: 720 x 1080 or 1440 x 2160 pixels
Box Art
This image may appear in various Store pages for Windows 10 (including Xbox), and if you don't provide the 9:16 Poster art image it will be used as your main logo. This image should also include your app’s name.
File format: .png
Maximum file size: 50MB
Aspect ratio: 1:1
Dimensions: 1080 x 1080 or 2160 x 2160 pixels
App Tile Icon
This image is required for proper display on Windows Phone 8.1 and earlier. If your previously-published app supports Windows Phone 8.1 or earlier, and you don't provide this image, those customers will see a blank icon with your app's listing. If your submission only includes UWP packages, you don’t need to provide this image.
File format: .png
Maximum file size: 50MB
Aspect ratio: 1:1
Dimensions: 300 x 300 pixels
Trailers are short videos that give customers a way to see your product in action, so they can get a better understanding of what it’s like. They are shown at the top of your app's Store listing (as long as you include a 16:9 Super Hero Art image). Trailers are encoded with Smooth Streaming, which adapts the quality of a video stream delivered to clients in real time based on their available bandwidth and CPU resources. (Note that trailers are only shown to customers on Windows 10, version 1607 or later, which includes Xbox.) You can add up to 15 trailers to your store listing.
File format: .mov or .mp4 (if you're uploading 4K video, only .mp4 is supported)
Video length: Minimal length, should not exceed 60 seconds
Maximum file size: 2GB
Dimensions: 1920 x 1080 or 3840 x 2160 pixels
Note that you should not include age ratings in your trailers.
If your trailer video is in the .mov file format:
- 1080p ProRes (HQ where appropriate)
- Native framerate; 29.97 FPS preferred
If your trailer video is in the .mp4 file format:
- Codec: h.264 (AVC1)
- Progressive scan (no interlacing)
- High Profile
- 2 consecutive B frames
- Closed GOP. GOP of half the frame rate.
- 50 MB/s
- Color Space: 4.2.0
Trailer Audio
If your trailer video is in the .mov file format:
- Stereo audio required
- Recommended Audio Level: -16 LKFS/LUFS
If your trailer video is in the .mp4 file format:
- Codec: AAC-LC
- Channels: Stereo or surround sound
- Sample rate: 48 KHz
- Audio Bitrate: 384 KB/s for Stereo, 512 KB/s for surround sound
Trailer Thumbnail Image
Each trailer must have a thumbnail image. This is typically a still image taken from the trailer.
File format: .png
Dimensions: 1920 x 1080 pixels
Windows 10 and Xbox Image (16:9 Super Hero Art)
In the Windows 10 and Xbox image section, the 16:9 Super hero art image is used in various layouts in the Microsoft Store on all Windows 10 device types (including Xbox). Select a dynamic image that relates to the app to drive recognition and differentiation. Don't include text in the image. Avoid showing your app's UI, and do not use any device-specific imagery. Avoid political and national themes, flags, or religious symbols. Don't include images of insensitive gestures, nudity, gambling, currency, drugs, tobacco, or alcohol. Don't use weapons pointing at the viewer or excessive violence and gore.
File format: .png
Dimensions: 1920 x 1080 or 3840 x 2160 pixels
Branded Key Art (Xbox)
Must include the product’s title. A branding bar is required on this image. Keep the title and all key imagery in the top three-quarters of the image, as an overlay may appear over the bottom quarter.
Dimensions: 584 x 800 pixels
Trailer Title
Each trailer must have a title which can be a maximum of 255 characters long.
Titled Hero Art (Xbox)
Must include the product’s title. Keep the title and all key imagery in the top three-quarters of the image, as an overlay may appear over the bottom quarter.
Dimensions: 1920 x 1080 pixels
Featured Promotional Square Art (Xbox)
Must not include the product’s title.
Dimensions: 1080 x 1080 pixels
Short Title (optional)
A shorter version of your product’s name. If provided, this shorter name may appear in various places on Xbox One (during installation, in Achievements, etc.) in place of the full title of your product. This field has a 50 character limit.
Sort Title (optional)
If your product could be alphabetised or spelled in different ways, you can enter another version here. This allows customers to find your product more quickly if they type that version in while searching. This field has a 255 character limit.
Voice Title (optional)
An alternate name for your product that, if provided, may be used in the audio experience on Xbox One when using Kinect or a headset. This field has a 255 character limit.
Short Description (optional)
A shorter, catchy description that may be used in the top of your product’s Store listing. If not provided, the first paragraph (up to 500 characters) of your longer description will be used instead. Because your description also appears below this text, Microsoft recommends providing a short description with different text so that your store listing isn’t repetitive. For games, the short description may also appear in the Information section of the Game Hub on Xbox One. For best results, keep your short description under 270 characters. The field has a 1000 character limit, but in some views, only the first 270 characters will be shown (with a link available to view the rest of the short description).
Additional System Requirements (optional)
If needed, you can describe the hardware configurations that your app requires to work properly (beyond the info you provided in the system requirements section in app properties.) You can enter up to 11 items for both minimum hardware and recommended hardware. These are displayed to the customer as a bulleted list in your store listing. Keep these brief, with just a few words (and no more than 200 characters) per item.
Search Terms (optional)
Search terms (formerly called keywords) are single words or short phrases that are not displayed to customers, but can help your make your app discoverable in the Store when customers search using those terms. You can include up to 7 search terms with a maximum of 30 characters each, and can use no more than 21 separate words across all search terms.
Copyright and Trademark Info (optional)
If you'd like to provide additional copyright and/or trademark info, enter it here. This field has a 200 character limit.
Additional License Terms (optional)
Leave this field blank if you want your app to be licensed to customers under the terms of the Standard Application License Terms (which are linked to from the App Developer Agreement). If your license terms are different from the Standard Application License Terms, enter them here. If you enter a single URL into this field, it will be displayed to customers as a link that they can click to read your additional license terms. This is useful if your additional license terms are very long, or if you want to include clickable links or formatting in your additional license terms. You can also enter up to 10,000 characters of text in this field. If you do that, customers will see these additional license terms displayed as plain text.
Developed By (optional)
Enter text here if you want to include a Developed by field in your app's Store listing. (The Published by field will list the publisher display name associated with your account, whether or not you provide a value for the Developed by field.) This field has a 255 character limit.
Publishing Hold Options
By default, Microsoft will publish your submission as soon as it passes certification (or per any dates you specified in the schedule section of the pricing and availability page). You can optionally choose to place a hold on publishing your submission until a certain date, or until you manually indicate that it should be published. The following options are available:
Publish your submission as soon as it passes certification (or per dates you specify)
Publish your submission manually
Start publishing your submission on a certain date
Notes for Certification
As you submit your app, you have the option to use the Notes for certification page to provide additional info to the certification testers. This info can help ensure that your app is tested correctly. Including these notes is particularly important for products that use Xbox Live Services and/or that require logging in to an account. If Microsoft can't fully test your submission, it may fail certification. Make sure to include the following (if applicable for your app):
User names and passwords for test accounts
Steps to access hidden or locked features
Steps to verify background audio usage
Expected differences in behaviour based on region or other customer settings
Info about what's changed in an app update
The date you're entering the notes
Anything else you think testers will need to understand about your submission
Restricted Capabilities
If your app declares any restricted capabilities, you must provide info during the app submission process in order to be approved to publish the app to the Microsoft Store. You provide this info on the Submission options page of your submission, explaining how your app uses each restricted capability that it declares.
Compliance with Microsoft Store Policies
Ensure that your game follows Microsoft's Store Policies.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Microsoft Docs - Publish Windows apps and games
Information about using the Partner Center to publish apps and games to the Microsoft Store.
Microsoft Docs - App submissions
App submission checklist.
Microsoft Docs - Microsoft Store Policies
The most recent version of Microsoft's Store Policies.
Link missing here or found errors? Improve How-Tos