JSON to C# Model Generator

JSON to C# Model Generator

The JSON to C# Model Generator converts JSON into C# classes so you can build .NET applications faster. It infers types from your JSON and produces class definitions with properties and getters/setters. This is ideal for ASP.NET APIs, client SDKs, and DTOs. The tool runs locally in your browser, so your data stays private.

Strongly typed models improve reliability by catching data mismatches at compile time. They also make serialization and deserialization easier with libraries like System.Text.Json or Newtonsoft.Json. Generating models from real JSON samples ensures your code matches the data you actually receive.

What this generator produces

• C# classes with auto-properties for each JSON field.
• Nested classes for nested objects.
• Lists for arrays (e.g., List<string>).
• Basic types: string, double, bool, object.

How to use the C# generator

1. Paste JSON on the left.
2. Click Generate Models.
3. Copy the C# output on the right.

Example: JSON to C#

Input JSON:

{
  "id": 1,
  "name": "Avi",
  "active": true,
  "roles": ["admin", "editor"],
  "profile": {
    "email": "avi@example.com",
    "score": 9.5
  }
}

Generated C# (simplified):

public class Root {
  public double id { get; set; }
  public string name { get; set; }
  public bool active { get; set; }
  public List<string> roles { get; set; }
  public Profile profile { get; set; }
}

public class Profile {
  public string email { get; set; }
  public double score { get; set; }
}

Handling arrays and nested objects

Arrays become List<T>, and nested objects become separate classes. If arrays contain objects, the generator creates a class for the object type and uses it in the list.

Common errors and fixes

• Invalid JSON: Fix syntax with JSON Validator.
• Mixed array types: Arrays with inconsistent types may cause object output. Normalize arrays.
• Null values: Nulls may become object. Provide non-null samples or use nullable types manually.
• Unexpected property names: JSON keys are used as property names. Rename or add [JsonPropertyName] attributes if needed.
• Missing fields: Include optional fields in your sample if you want them generated.

Best practices for C# models

• Use representative JSON samples that cover all fields.
• Add nullable types (e.g., int?, double?) for optional fields.
• Apply serialization attributes for naming mismatches.
• Validate JSON with JSON Schema Validator for strict contracts.
• Store models in a shared project for reuse across services.

Serialization attributes

When JSON keys do not match C# property naming, add [JsonPropertyName] for System.Text.Json or [JsonProperty] for Newtonsoft.Json. This ensures stable mapping without changing property names. For example:

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

Nullability and optional fields

In modern C#, enable nullable reference types to catch missing fields early. If a property can be absent, mark it nullable (e.g., string? or int?). This improves safety when working with real-world APIs where fields can be omitted.

Records vs classes

If you prefer immutable models, convert generated classes into records. Records offer value-based equality and concise syntax, which is helpful for DTOs and API responses. Use classes when you need mutable models or serialization frameworks that expect setters.

Use cases

ASP.NET APIs: Generate DTOs for request and response payloads.

Client SDKs: Build typed models for client applications.

Data ingestion: Deserialize JSON feeds into C# objects.

Testing: Create strongly typed fixtures for unit tests.

Common pitfalls

• Dates as strings: Dates are inferred as strings. Parse to DateTime manually if needed.
• Mixed array types: Normalize arrays to ensure a single element type.
• Numbers as strings: If numeric values arrive as strings, adjust types manually.
• Deep nesting: Consider splitting models into smaller classes.

.NET integration tips

Use System.Text.Json with [JsonPropertyName] attributes for custom JSON names. If you prefer Newtonsoft.Json, use [JsonProperty]. For validation, combine models with data annotations like [Required] or [StringLength].

If you use ASP.NET, model binding will automatically map JSON to your classes. For strict validation, enable model validation filters so invalid payloads return clear errors.

Nullable reference types

Enable nullable reference types in your project to catch missing fields at compile time. Mark optional reference properties as string? and use ? for nullable value types. This helps you avoid null reference exceptions when dealing with partial API responses.

Naming policies

System.Text.Json uses camelCase by default. If your JSON uses snake_case, set a naming policy or use [JsonPropertyName] attributes. Keeping naming consistent reduces mapping errors and makes debugging easier.

Workflow checklist

1. Validate JSON input.
2. Generate C# models.
3. Refine property names and add attributes.
4. Use in serializers or API clients.
5. Update models when the API changes.

Testing and validation

Create a quick unit test that deserializes a sample JSON into the generated model. This confirms property mapping works as expected. If you have a JSON Schema, validate the JSON before deserialization to catch issues early.

Use cases

Web APIs: Bind incoming JSON to strongly typed DTOs.

Desktop apps: Parse JSON configs into typed objects.

Integration services: Validate and transform JSON data safely.

Testing: Generate fixtures and compare outputs reliably.

FAQs

Does this generate classes or records?
It generates classes with properties. Convert to records if you prefer.

Is my JSON uploaded?
No. Everything runs locally in your browser.

How do I handle enums?
Define enums manually and replace the generated property types.

Can I generate models for arrays?
Yes. Arrays are represented as List<T>.

Can I use this for API clients?
Yes. The output works well with HttpClient and serializers.

What about nullable fields?
Add nullable types manually based on your API rules.

Does it handle nested arrays?
Yes. Nested arrays generate nested list types.

How do I keep models updated?
Regenerate models when payloads change and compare diffs.

Can I use these models in EF Core?
Yes, but add EF Core attributes manually if you want entity mapping.

Does it support records?
The generator outputs classes. Convert to records manually if desired.

Can I add validation attributes?
Yes. Add data annotations like [Required] after generation.

Do I need to regenerate for every change?
Regenerate when the JSON contract changes, and compare diffs.

Can I generate one model per file?
Yes. Split classes into separate files after generation if preferred.