# json5Allowed Specifies that reading serialized JSON data supports the JSON5 syntax. ``` static var json5Allowed: JSONSerialization.ReadingOptions { get } ``` ## Discussion The JSON5 Data Interchange Format is a superset of JSON that enhances human-readability of the JSON syntax. The JSON5 standard allows the following: - Single- or double-quoted strings. - Strings that span multiple lines. - Single- and multiline comments, using `//` and `/* … */` syntax. - Enhanced number formatting support, including hexadecimal, leading or trailing decimal point, explicit plus sign, and IEEE 754 positive infinity, negative infinity, and `NaN`. ### Using JSON5 in Attributed Strings The Markdown syntax supported by [`AttributedString`](/documentation/Foundation/AttributedString) uses JSON5 to support an extended attribute syntax. Automatic grammar agreement uses this syntax for its `inflect` attribute, as do custom attributes defined by third-party frameworks. Use the syntax `^[text](attribute: value)` to mark ranges of text decorated with a custom attribute, like this: ```other This is a [Markdown](https://commonmark.org) string with a ^[custom attribute](factor: 10). ``` This example applies a custom attribute called `factor` with a value of `10` to the text “custom attribute” in the resulting attributed string. The portion inside the parentheses is JSON5. [`AttributedString`](/documentation/Foundation/AttributedString) also uses the [`topLevelDictionaryAssumed`](/documentation/Foundation/JSONSerialization/ReadingOptions/topLevelDictionaryAssumed) option; without it, the Markdown string would have to wrap everything inside the parentheses with braces. --- 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)