# Overview

The `Hermodr.Schema` package adds the ability to formally describe the structure of your events — what properties they carry, their types, and constraints — and to validate `CloudEvent` instances against those descriptions before publishing.

## Installation

```bash
dotnet add package Hermodr.Schema
```

## What's included

| Type                           | Role                                                        |
| ------------------------------ | ----------------------------------------------------------- |
| `IEventSchema` / `EventSchema` | The schema model                                            |
| `EventSchemaBuilder`           | Fluent API for building a schema in code                    |
| `EventSchemaCreator`           | Derives a schema from an annotated class using reflection   |
| `IEventSchemaFactory`          | DI-friendly factory wrapping `EventSchemaCreator`           |
| `IEventSchemaWriter`           | Abstraction for schema serialisation (JSON, YAML, AsyncAPI) |
| `EventSchemaJsonWriter`        | Serialises a schema to JSON                                 |
| `IEventSchemaValidator`        | Validates a `CloudEvent` against a schema                   |

## Pages in this section

| Page                                                   | Description                                      |
| ------------------------------------------------------ | ------------------------------------------------ |
| [Fluent Builder](/event-schema/fluent-builder.md)      | Build a schema programmatically                  |
| [From Annotations](/event-schema/from-annotations.md)  | Derive a schema from `[Event]`-annotated classes |
| [Export as JSON](/event-schema/export-json.md)         | Serialise a schema to a JSON document            |
| [Export as YAML](/event-schema/export-yaml.md)         | Serialise a schema to a YAML document            |
| [Export as AsyncAPI](/event-schema/export-asyncapi.md) | Generate complete AsyncAPI 2.x documents         |
| [Validation](/event-schema/validation.md)              | Validate `CloudEvent` instances against a schema |

## Schema model at a glance

An `IEventSchema` carries:

* **`Type`** — the event type string (e.g. `"order.placed"`)
* **`Version`** — the SemVer version of the schema
* **`ContentType`** — MIME type of the event data
* **`Description`** — human-readable description
* **`Properties`** — a collection of `IEventProperty` entries, each with:
  * `Name`, `DataType`, `Description`
  * Constraints: `Required`, `Nullable`, `Range<T>`, `Enum`


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