--- title: Discovering asset specifications framework: App Store Connect API role: article role_heading: Article path: appstoreconnectapi/discovering-asset-specifications --- # Discovering asset specifications Query the asset library reference data to learn the valid dimensions, formats, placement groups, and limits before you upload. ## Overview Overview The App Asset Library validates every asset against a catalog of specifications, and it exposes that catalog through the appAssetLibraryRefData resource. Reading it at runtime is the difference between an integration that keeps working and one that falls behind when Apple adds a device. An integration that hard-codes specifications or placement group identifiers can’t target a new device family, and may reject files that a new specification accepts, until you ship an update. The catalog is large. It holds dozens of image specifications, more than a dozen video specifications, and dozens of placement groups, and it changes as the App Store changes. Reference data is read-only, and its identifiers are strings rather than enumerations precisely so new device families can appear without an API change. Don’t hard-code them. For the resource reference, see App Asset Library reference data. For the concept, see Understanding the App Asset Library. Read the reference data Fetch the catalog with GET /v1/appAssetLibraryRefData (List app asset library ref data). The collection holds a single AppAssetLibraryRefDatum with attributes that are six parallel arrays: Narrow the response with filter[features], filter[placementTypes], filter[placementProfileGroups], or filter[specs], or use fields[appAssetLibraryRefData] to request only the arrays you need. Reading one array instead of all six keeps a routine specification check small: GET /v1/appAssetLibraryRefData?fields[appAssetLibraryRefData]=imageSpecs Follow the lookup chain The six arrays are designed for traversal in order. To find the file you need for an iPhone screenshot on an App Store version, walk them like this: Start with the feature. Find APP_STORE_VERSIONS in features. Its placementPolicies list the placement types that feature supports, and for each one, groupLimits gives the maxCount allowed per set of groupIds. Pick a placement group. Look up your target group in placementProfileGroups to confirm its platform and display class, for example, IPHONE_DYNAMIC_ISLAND_LARGE_PROFILE or MAC_PROFILE. Map the group to specifications. Find your placement type in placementTypes, then find your group in its specMappings. The specs array lists the specification IDs that group accepts. Read the specification. Look each ID up in imageSpecs or videoSpecs to get the actual requirements. An image specification looks like this: { "specId": "f56c777c-99ea-5760-97ae-27c5f8cbb884", "shortName": "i1290x2796a0", "dimensions": { "minWidth": 1290, "maxWidth": 1290, "minHeight": 2796, "maxHeight": 2796 }, "aspectRatio": "6:13", "compatiblePlacementTypes": ["APP_SCREENSHOT", "IMESSAGE_APP_SCREENSHOT"], "alphaAllowed": false, "fileExtensions": [".jpg", ".jpeg", ".png"], "mimeTypes": ["image/jpeg", "image/png"], "maxFileSize": 524288000, "universalAsset": false } For screenshots and previews, minWidth equals maxWidth and minHeight equals maxHeight, so the dimensions are exact, not a range. Resize to match before you upload. When you’re working backward from a file you already have, use compatiblePlacementTypes to skip the chain: Given a specification, it lists every placement type that accepts it. Understand universal assets A specification with universalAsset set to true satisfies several placement types at once. Check compatiblePlacementTypes on the specification to see which ones. Uploading one file at a universal specification and creating a placement per type is less work than producing a file for each. Respect the placement limits groupLimits caps how many assets a placement group holds. For APP_STORE_VERSIONS, the App Store allows 10 screenshots, 3 app previews, and 1 product page header asset per group. In-app events allow a single asset for each of their placement types. Read the limit rather than assuming it. Creating placements past the cap fails, and the limits differ by feature: custom product pages and product page optimizations carry their own policies, and they don’t always match the App Store version policies. Match the asset category Each entry in placementTypes lists an acceptsAssetCategories array. APP_SCREENSHOT and IMESSAGE_APP_SCREENSHOT accept APP_SCREENSHOTS_AND_PREVIEWS; the creative placement types such as EVENT_CARD_ASSET and PRODUCT_PAGE_HEADER_ASSET accept CREATIVE_ASSETS. Because you set an asset’s category when you reserve it and can’t change it afterward, check this before uploading. You can’t place an asset where you intend if it has the wrong category. note: AppAssetLibraryFeature enumerates more features than the reference data currently returns. Iterate over the features array you receive rather than over the enumeration, and treat a feature that’s absent as unavailable for your app. Cache with care The catalog is stable within a session but not permanent; Apple adds specifications and groups as new devices ship. Fetch it when your integration starts rather than embedding a copy, and key your logic on the identifiers you read back. Two habits make the difference: Resolve a specId returned on an asset by looking it up in the catalog, instead of comparing against a hard-coded list. Treat an unrecognized placement group or specification ID as a signal to refresh, not as an error. To read a specific reference data resource by ID, use GET /v1/appAssetLibraryRefData/{id} (Read an app asset library ref data). After you know the specification you need, upload the asset. For more information, see Uploading and managing image assets and Uploading and managing video assets. ## See Also ### Essentials - [Understanding the App Asset Library](appstoreconnectapi/understanding-the-app-asset-library.md) - [Uploading and managing image assets](appstoreconnectapi/uploading-and-managing-image-assets.md) - [Uploading and managing video assets](appstoreconnectapi/uploading-and-managing-video-assets.md) - [Placing assets on your App Store surfaces](appstoreconnectapi/placing-assets-on-your-app-store-surfaces.md) - [Migrating to the App Asset Library](appstoreconnectapi/migrating-to-the-app-asset-library.md)