# Export as JSON

`EventSchemaJsonWriter` serialises an `IEventSchema` to a JSON stream. It is included in the `Hermodr.Schema` package — no extra installation required.

## Usage

```csharp
using Hermodr;
using System.Text.Json;

var schema = EventSchema.FromDataType<OrderPlacedData>();

var writer = new EventSchemaJsonWriter(new JsonWriterOptions { Indented = true });

await using var stream = File.OpenWrite("order-placed-schema.json");
await writer.WriteToAsync(stream, schema);
```

## `JsonWriterOptions`

Pass a `System.Text.Json.JsonWriterOptions` instance to control formatting:

| Option     | Default | Effect                       |
| ---------- | ------- | ---------------------------- |
| `Indented` | `false` | Pretty-print the JSON output |
| `Encoder`  | `null`  | Custom character encoder     |

## Output format

```json
{
  "type": "order.placed",
  "version": "1.0",
  "contentType": "object",
  "description": "Raised when a customer places an order",
  "properties": {
    "OrderId": {
      "dataType": "guid",
      "required": true
    },
    "Amount": {
      "dataType": "money",
      "required": true,
      "min": 0.01,
      "max": 1000000
    },
    "Currency": {
      "dataType": "string",
      "required": true
    },
    "Notes": {
      "dataType": "string",
      "nullable": true
    }
  }
}
```

## Writing to a string

```csharp
await using var memStream = new MemoryStream();
await writer.WriteToAsync(memStream, schema);
var json = Encoding.UTF8.GetString(memStream.ToArray());
```

## `IEventSchemaWriter` interface

`EventSchemaJsonWriter` implements `IEventSchemaWriter`:

```csharp
public interface IEventSchemaWriter
{
    Task WriteToAsync(Stream stream, IEventSchema schema, CancellationToken cancellationToken = default);
}
```

You can register and resolve it via DI if you prefer not to instantiate it directly.

## Related pages

* [Export as YAML](/event-schema/export-yaml.md)
* [Export as AsyncAPI](/event-schema/export-asyncapi.md)
* [Fluent Builder](/event-schema/fluent-builder.md)
* [From Annotations](/event-schema/from-annotations.md)


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