How to use it
- Paste a JSON object or array into the input panel.
- Choose record or class, then adjust nullability, type detection and the serializer.
- Copy the generated types straight into your project.
What the generator decides for you
Turning JSON into C# is mostly a series of small judgement calls, and this is what this tool picks.
Numbers. An integer becomes int, or long when it exceeds int.MaxValue. A number with a fractional part becomes double, or decimal if you ask for it. This is a genuine guess: JSON has exactly one number type, so 1 and 1.0 are indistinguishable in the payload even though they are different C# types. If a field is sometimes fractional, the sample you paste may not show it.
Strings that are not really strings. With detection enabled, a value matching the GUID format becomes Guid, and an ISO 8601 timestamp becomes DateTimeOffset — preferred over DateTime because it keeps the offset rather than silently reinterpreting it in local time.
Names. display_name becomes DisplayName with a [JsonPropertyName("display_name")] attribute. The attribute is only emitted when the C# name differs from the JSON name, so PascalCase payloads produce clean, attribute-free types. Names colliding with C# keywords get the @ prefix.
Shape merging. Two objects with identical keys and types become one type rather than two identical ones. This is what keeps output from a large payload readable.
Nullable reference types are the part people get wrong
With <Nullable>enable</Nullable> — the default in new .NET projects — the compiler tracks which references may be null. Deserializers ignore that entirely.
System.Text.Json will happily leave a non-nullable string Name { get; init; } as null if the JSON omits the property or sets it to null. The compiler thought it was guaranteed; at runtime it is not. You then get a NullReferenceException far from the cause, in code the compiler told you was safe.
Two honest options: mark properties string? and handle absence explicitly, or keep them non-nullable and validate immediately after deserialization. Silently initialising to string.Empty — which this generator does when you turn nullability off — hides missing data rather than surfacing it. Pick deliberately.
System.Text.Json versus Newtonsoft.Json
System.Text.Json is the default in modern .NET: faster, allocation-light, built in. Its strictness catches people migrating — it is case-sensitive unless configured otherwise, rejects trailing commas and comments by default, and will not coerce a JSON string into a number.
Newtonsoft.Json remains the pragmatic choice when you need TypeNameHandling, JsonConverter behaviour that has no modern equivalent, or a large existing codebase that relies on its permissive defaults. Switch the serializer option above and the attributes change from JsonPropertyName to JsonProperty accordingly.
Generated code is a starting point
Treat the output as scaffolding, not as a finished model. A generator sees one payload; it cannot know which fields are optional, which strings are really enums, which lists are never empty, or which double should have been decimal. Paste it in, then tighten the types against the API's actual documentation.