JSON to C# classes

How to use it#

1. Paste a JSON sample into the box above, such as a response from the API you are calling.
2. Name the root class, and choose classes or records.
3. Pick the library that will read the JSON, so each property gets the right attribute.
4. Copy the C# from beside the result, or download it as a .cs file.

How the C# types are chosen#

Text becomes string and true or false becomes bool. A number becomes int when every value seen in that place is a whole number that fits in 32 bits, long when one of them is larger, decimal when one is too big even for long, and double as soon as one has a fractional part. A price written as 12.0 counts as whole, since the zero is lost when the JSON is read, so include one real price such as 12.5 or change the type by hand. An object becomes a class of its own, named after the key it sits under, so a shipping_address key gives a ShippingAddress class, an array becomes a List of whatever it holds, and an object with no keys becomes Dictionary<string, object>.

Keys are turned into PascalCase property names, and every property keeps an attribute naming its JSON key exactly, so first_name maps to FirstName and still reads and writes as first_name. A key that would clash with its class name, or with another key once both are in PascalCase, is given a suffix rather than left to break the build.

A place that holds two different kinds of value, such as a number in one record and a string in another, or that the sample says nothing about, such as an empty array, becomes object. That compiles and deserializes, and it is the honest answer: the sample does not say which type it should be.

Nulls, missing keys, and nullable types#

A value that is null in the sample, or a key that some objects in an array leave out, gets a question mark: int? or string?. That is what lets the deserializer leave it empty rather than throw or silently store a zero. Keys present in every sample come out without one.

With nullable reference types switched on, the compiler warns about a string or List property that has no question mark and no value set in a constructor. Add the required modifier where the API always sends the field, or a default such as string.Empty, depending on how your project handles it. The sample alone cannot tell which fields the API promises.

Classes or records#

A class with get and set is the long-standing choice and works with every serializer and every version of .NET. A record with init accessors gives you value equality and properties that cannot be changed after the object is built, which suits a response you only read. System.Text.Json and Newtonsoft.Json both fill init properties, so pick whichever your codebase already uses.

When the JSON at the top level is an array or a single value rather than an object, C# has no way to name that type, so the output starts with a comment saying what to deserialize it as, such as List<RootItem>. Read the JSON into the model with JsonSerializer.Deserialize<Root>(json) in System.Text.Json, or JsonConvert.DeserializeObject<Root>(json) in Newtonsoft.Json. For the same model in TypeScript, use JSON to TypeScript, and for Go structs, JSON to Go.