---
title: contentRulesJSON()
framework: mailkit
role: symbol
role_heading: Instance Method
path: mailkit/mecontentblocker/contentrulesjson()
---

# contentRulesJSON()

The rules, as JSON data, that the system applies when it displays a message.

## Declaration

```swift
func contentRulesJSON() -> Data
```

## Return Value

Return Value A data object that contains valid JSON content.

## Discussion

Discussion MailKit relies on WebKit to block content. Therefore, the JSON structure is the same that a content blocker extension for Safari uses. For details about the structure of the JSON to specify the content-blocking rules, see Introduction to WebKit Content Blockers. The following code shows an example of a content blocker that uses a rule to hide all links from a specific domain: func contentRulesJSON() -> Data {     // A single rule that visually hides all links to example.com.     let rules = [         [             "action": [                 "type": "css-display-none",                 "selector": "a[href*='example.com']"             ],             "trigger": [ "url-filter": ".*" ]         ]     ]          // Serialize the array of rules to JSON.     let data = try? JSONSerialization.data(withJSONObject: rules, options: [])          // Return the encoded rules, or an empty data if encoding failed.     return data ?? Data() }