Json schema validation in .NET

Validating JSON documents against a JSON schema is useful in many scenarios, such as verifying data received from a REST API or validating a user-authored configuration file.

.NET doesn't support JSON schema validation out of the box. However, several third-party libraries are available for this purpose. This post uses the JsonSchema.Net library (GitHub).

Let's create the project:

dotnet new console
dotnet add package JsonSchema.Net

The following code snippet validates JSON data against a JSON schema:

using System.Text.Json.Nodes;
using Json.Schema;

var schema = """
    {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "$id": "https://example.com/product.schema.json",
      "title": "Product",
      "description": "A product from Acme's catalog",
      "type": "object",
      "properties": {
        "productName": {
          "description": "Name of the product",
          "type": "string"
        },
        "price": {
          "description": "The price of the product",
          "type": "number",
          "exclusiveMinimum": 0
        }
      },
      "required": [ "productName", "price" ]
    }
    """;

var invalidJson = """
    {
        "productName": "test",
        "price": -1
    }
    """;

// Validate the JSON data against the JSON schema
var jsonSchema = JsonSchema.FromText(schema);
var result = jsonSchema.Evaluate(JsonNode.Parse(invalidJson));
if (!result.IsValid)
{
    Console.WriteLine("Invalid document");
    if (result.HasErrors)
    {
        foreach (var error in result.Errors)
        {
            Console.WriteLine(error.Key + ": " + error.Value);
        }
    }
}

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