Printing valid JSON with a Swift script

I would recommend using do {} catch { () } block, and before serialization do check if its a valid JSON object.

           do {

                    if let result = responseObj.result, JSONSerialization.isValidJSONObject(result) {

                        let jsonData = try JSONSerialization.data(withJSONObject: result)

                        // Convert to a string and print
                        if let JSONString = String(data: jsonData, encoding: String.Encoding.utf8) {
                            print(JSONString)
                        }
                    }
                } catch {
                    ()
                }

Happy coding.

Swift 4.2 Extension
Looked up @smarx solution a lot of times to print my JSON string. Eventually ended up making an extension

extension Data
{
    func printJSON()
    {
        if let JSONString = String(data: self, encoding: String.Encoding.utf8)
        {
            print(JSONString)
        }
    }
}

Two issues:

1. You don't have the structure you ultimately want. You have an array with one item in it, and that item is a dictionary. Based on your expected output, you seem to just want a dictionary. You can fix this by dropping the extra square brackets.
2. JSON is a serialization format. You don't have "a JSON object." You have data that you would like to serialize as JSON. You can do that with JSONSerialization.

Here's working code that produces the expected output:

#! /usr/bin/swift

import Foundation

// Drop the extra brackets, and use a type annotation
let metadata: [String: Any] = [
    "iid": "org.albert.extension.external/v2.0",
    "name": "Tomboy",
    "version": "0.1",
    "author": "Will Timpson",
    "dependencies": ["tomboy", "python-pydbus"],
    "trigger": "tb"
]

// Serialize to JSON
let jsonData = try JSONSerialization.data(withJSONObject: metadata)

// Convert to a string and print
if let JSONString = String(data: jsonData, encoding: String.Encoding.utf8) {
   print(JSONString)
}

// Output:
// {"iid":"org.albert.extension.external\/v2.0","name":"Tomboy","version":"0.1","dependencies":["tomboy","python-pydbus"],"author":"Will Timpson","trigger":"tb"}

Swift 4:

If you want a quick dirty one liner just for example, checking the serialised JSON Data you are about to attach to a http request body then I use the following:

let json = NSString(data: myJsonObject, encoding: String.Encoding.utf8.rawValue)
print(json)

It prints as clear JSON, no added slashes or anything!