JSON to C# Class

How the JSON to C# Class works

The generator parses your JSON and records the kinds of values found at every position. All objects at the same position, such as every item of an array, are merged into one class, so a sample with several items gives better results than a single item. Nested objects become their own classes named after the property, and array item classes use the singular form of the property name, so items produces an Item class.

Types are chosen as follows: string, bool, int for whole numbers that fit in 32 bits and long for larger ones (decided from the original digits, so large IDs are not rounded), double or decimal for numbers with a fraction or exponent, DateTime for strings that are all ISO 8601 dates, and List<T> for arrays. When a property holds different kinds of values, or only null, its type is object. A value type becomes nullable, such as int?, when the property is null in any sample or missing from some of the merged objects.

Property names are converted to PascalCase. With System.Text.Json or Newtonsoft.Json attributes selected, each property also gets an attribute with the original JSON key, so user_name still maps to UserName. When the top-level JSON is an array, the root class describes its items and a comment reminds you to deserialize it as a list.

How to use the JSON to C# Class

1. Paste a sample JSON object or array of objects into the input box, open a .json file, or select Load example.
2. Set the root class name and an optional namespace, choose System.Text.Json, Newtonsoft.Json or no attributes, and pick the types for whole and decimal numbers.
3. Select Generate C#, or press Ctrl + Enter (Cmd + Enter on a Mac).
4. Copy the classes into your project or download them as a .cs file.

Example

This input:

{"id": 90071992547409931, "user_name": "ann", "createdAt": "2024-05-01T10:30:00Z",
 "items": [{"sku": "KB-1", "qty": 1}, {"sku": "MS-2", "qty": null}]}

produces, with the default options:

using System;
using System.Collections.Generic;
using System.Text.Json.Serialization;

public class Root
{
    [JsonPropertyName("id")]
    public long Id { get; set; }

    [JsonPropertyName("user_name")]
    public string UserName { get; set; }

    [JsonPropertyName("createdAt")]
    public DateTime CreatedAt { get; set; }

    [JsonPropertyName("items")]
    public List<Item> Items { get; set; }
}

public class Item
{
    [JsonPropertyName("sku")]
    public string Sku { get; set; }

    [JsonPropertyName("qty")]
    public int? Qty { get; set; }
}

Common use cases

• Creating DTOs for a third-party REST API from an example response.
• Generating request and response models for ASP.NET Core or ASP.NET Web API controllers.
• Building classes to deserialize JSON configuration or message queue payloads.
• Starting a strongly typed client for a webhook whose documentation only shows sample JSON.

Common errors and how to fix them

The JSON must be an object, or an array of objects, to generate C# classes

A bare string, number, or an array of primitives has no properties to turn into a class. Paste a sample object, or an array whose items are objects.

A property was generated as object

That field was null in every record you supplied, so there is no type information to infer from. Provide a sample where the field has a real value, or set the property type by hand afterwards.

Deserialisation returns nulls at runtime

Check the attribute option you generated with. Without attributes, your serialiser must be configured with a naming policy that matches the JSON keys; choosing the System.Text.Json or Newtonsoft option emits explicit attributes instead, which removes the guesswork.

A number came out as the wrong type

Types are inferred from the sample you provide, so a value of 1 is inferred as int even if the same field holds a decimal elsewhere. Supply a representative sample, or widen the type after generating.

Frequently asked questions