# data(withJSONObject:options:) Returns JSON data from a Foundation object. ``` class func data(withJSONObject obj: Any, options opt: JSONSerialization.WritingOptions = []) throws -> Data ``` ## Parameters `obj` The object from which to generate JSON data. Must not be `nil`. `opt` Options for creating the JSON data. See [`JSONSerialization.WritingOptions`](/documentation/Foundation/JSONSerialization/WritingOptions) for possible values. ## Return Value JSON data for `obj`, or `nil` if an internal error occurs. The resulting data is encoded in UTF-8. ## Discussion If `obj` can’t produce valid JSON, [`JSONSerialization`](/documentation/Foundation/JSONSerialization) throws an exception. This exception occurs prior to parsing and represents a programming error, not an internal error. Before calling this method, you should check whether the input can produce valid JSON by using [`isValidJSONObject(_:)`](/documentation/Foundation/JSONSerialization/isValidJSONObject(_:)). Setting the [`prettyPrinted`](/documentation/Foundation/JSONSerialization/WritingOptions/prettyPrinted) option generates JSON with white space designed to make the output more readable. If this option isn’t set, [`JSONSerialization`](/documentation/Foundation/JSONSerialization) generates the most compact possible JSON. > Handling Errors in Swift: > In Swift, this method returns a nonoptional result and is marked with the `throws` keyword to indicate that it throws an error in cases of failure. > > You call this method in a `try` expression and handle any errors in the `catch` clauses of a `do` statement, as described in [Error Handling](https://docs.swift.org/swift-book/LanguageGuide/ErrorHandling.html) in [The Swift Programming Language](https://docs.swift.org/swift-book/) and `About Imported Cocoa Error Parameters`. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)