C#, how to validate JSON using Regex

Just an idea, why not deserialyze data first and then validate fields:

var serializer = new JavaScriptSerializer();
dynamic obj = serializer.Deserialize(json, typeof(object));

Then you can validate: obj.Id, obj.Value, obj.isGood

If you're not forced to use RegEx and you just need a syntax check of JSON data for debugging purpose, try the online tool

http://jsonlint.com/

which does the job fine (caution: do not paste sensitive data!).

Example: If you paste the data

{
    "Id": 123,
    "Value": "asdf",
    "Time": "adf",
    "isGood": false
}]

You're getting the result:

Parse error on line 6:

... "isGood": false}]

------------------------^ Expecting 'EOF'

If you do have to validate sensitive data, you can look at the source code, which is available at GitHub:

https://github.com/arc90/jsonlintdotcom.

There is also a pure JS version available: https://github.com/zaach/jsonlint.

If you intend to do a schema-based validation, e.g. to determine if the JSON data consists of the right data types, look here:

https://stackoverflow.com/questions/19544183/validate-json-against-json-schema-c-sharp

N.B. RegEx can only parse regular grammars; for anything context-free and higher you need a stack (i.e. a real parser). This is why the solutions shown here are not using RegEx - regular expressions are typically used to parse number formats, the format of domain names, email addresses etc. For this purpose, they are doing the job good. For real parsing tasks as mentioned above better use a real parser.

I tried to validate using what is commented in the accepted answer without success using this regex pattern:

 {("\w+":(\d+|"\w+"|true|false|null))+}\]

I tried with this pattern {[^}]+} and now I have a good validation:

            WebClient client = new WebClient();
            string myJSON = client.DownloadString(jsonFile);
         
            //var regex = @"{(\w+:(\d+|\w + |true|false|null))+}\]";
            var regex = @"{[^}]+}";
            var match = Regex.Match(myJSON, regex, RegexOptions.IgnoreCase);
            if (!match.Success)
            {
                Debug.WriteLine("* JSON NOT VALID.");                   
            }
            else
            {
                Debug.WriteLine("* JSON VALID.");                   
            }

I think this is already solved with above solutions, but if you are looking for a very clean approach to this where only a single line of code does your job then you might wanna check this open source library I have created:

Its open, scalable and provides enough utilities for most of the requirements. Define a class as you normally would, rest of things are taken care by the library. It will recursively search entire JSON while parallely comparing it to your predefined class.

https://github.com/anirudha-stack/JsonScrutinize

https://www.nuget.org/packages/JsonScrutinize

Nested json is supported, you can get Mismatched type keys, null keys and missing keys from this.

Quick Start Guide: Install via NuGet

Install-Package JsonScrutinize

Define your C# class with validation attributes:

public class User
{
    [Required]
    public string Name { get; set; }
    
    [RegularExpression(@"^[A-Za-z]+$")]
    public string Role { get; set; }
}

Validate your JSON:

string json = "{\"Name\": \"John Doe\", \"Role\": \"Admin123\"}";
JsonScrutinize scrutinizer = new JsonScrutinize();
var result = await scrutinizer.KeyTypeScrutinize(json, typeof(User));

Expected Output:

{
    "StatusCode": "S201",
    "Description": "Found 1 mismatched key in the provided JSON",
    "MismatchedKeys": [
        "Role"
    ]
}

You can also check the source code of it in the github release.

Happy coding :)