--- title: Defining file and data types for your app framework: uniformtypeidentifiers role: article role_heading: Article path: uniformtypeidentifiers/defining-file-and-data-types-for-your-app --- # Defining file and data types for your app Declare uniform type identifiers to support your app’s proprietary data formats. ## Overview Overview Apps that save, load, or transfer documents with proprietary data formats can define the file or data type for each format by: Declaring your app’s custom type in the project’s Info.plist file. Creating a new identifier for exported types, or using existing identifiers for imported types. Defining each type’s conformance to system-declared types Listing any associated file extensions or MIME types. Declare a custom type for your app When defining a type, you need to define it as an exported or imported type; this declaration indicates whether your app is the source of the type or whether it supports using a type defined elsewhere, respectively. If your app uses a type that this framework provides, don’t redeclare it in your app’s bundle. Define an exported type when your app is the canonical source of information for that type. For example, if your app uses its own proprietary document format, declare it as an exported type. Define an imported type if your app uses a type that another app defines, or if it’s a proprietary file format the system doesn’t declare. When importing a type from another app, don’t declare your own identifier; instead, use the same type identifier as the original. Choose an identifier for your type The identifiers you create for your app need to be unique. To ensure uniqueness, start by using a reverse DNS format that begins with com.companyName. Although the system supports different type identifier strings with the same specification, the reverse isn’t true. The identifier must contain only alphanumeric characters (a–z, A–Z, and 0–9), hyphens (-), and periods (.). For example, you might use com.example.greatAppDocument or com.example.greatApp-document for the UTTypeIdentifier string in the Info.plist file. important: Don’t use public, dyn, or com.apple as the prefix in your app’s types. The system reserves public for public domain or standard types. The framework reserves the prefix dyn for types that it generates dynamically when no other type is available, and the prefix com.apple for types that Apple declares. Define the conformance The type declaration can include a list of type identifiers that the type conforms to. For example, if your app uses a proprietary file format based on JSON, use public.json in the UTTypeConformsTo string in the Info.plist file. When defining a document type, make sure that it conforms to public.data or com.apple.package to ensure the Finder or Files app can represent it. If your type doesn’t conform to public.data or com.apple.package, the system can’t tell if a stored item has that type. For document types, conform to public.content, either directly or by conforming to a type that already conforms to public.content. This conformance allows users to share your type over AirDrop. You can also add conformance to functional types, such as public.database or public.spreadsheet. Conform your type to the most specific subtype applicable. Conforming to one or more functional types helps the system determine how best to display your app’s file types. If you specify conformance to a nonpublic type, make sure that you also declare that type in your bundle. Define the description, extensions, and MIME types In addition to declaring the identifier, the type can define a user-readable string describing the type that you can also localize. For example, you might use GreatApp Document for the UTTypeDescription string in the Info.plist file. Add a UTTypeTagSpecification dictionary in the Info.plist file to define the file extension or MIME types for your type. For example, add the string greatappdoc and greatapp into an array, and put it into the UTTypeTagSpecification dictionary with the key public.filename-extension to support both as file extensions for your type. The following sample shows the exported example type added to an Info.plist file: UTExportedTypeDeclarations UTTypeIdentifier com.company.greatApp-document UTTypeConformsTo public.json UTTypeDescription GreatApp Document UTTypeTagSpecification public.filename-extension greatappdoc greatapp Specify the keys for declaring a type The following table lists the available property keys that you use in type declarations: | | | | | | | | | | | | | | | | If both exported and imported declarations for a type exist, the exported declaration takes precedence over the imported declaration. ## See Also ### Essentials - [System-declared uniform type identifiers](uniformtypeidentifiers/system-declared-uniform-type-identifiers.md)