cadl/packages/json-schema/README.md

# @typespec/json-schema

TypeSpec library for emitting TypeSpec to JSON Schema and converting JSON Schema to TypeSpec

## Install

```bash
npm install @typespec/json-schema
```

## Usage

Add the `@jsonSchema` decorator to any types or namespaces you want to emit as JSON Schema.

```TypeSpec
import "@typespec/json-schema";

using TypeSpec.JsonSchema;

@jsonSchema
namespace Example;

model Car {
  make: string;
  model: string;
}
```

## Usage

1. Via the command line

```bash
tsp compile . --emit=@typespec/json-schema
```

2. Via the config

```yaml
emit:
  - "@typespec/json-schema"
```

The config can be extended with options as follows:

```yaml
emit:
  - "@typespec/json-schema"
options:
  "@typespec/json-schema":
    option: value
```

## Emitter options

### `file-type`

**Type:** `"yaml" | "json"`

Serialize the schema as either yaml or json.

### `int64-strategy`

**Type:** `"string" | "number"`

How to handle 64 bit integers on the wire. Options are:

- string: serialize as a string (widely interoperable)
- number: serialize as a number (not widely interoperable)

### `bundleId`

**Type:** `string`

When provided, bundle all the schemas into a single json schema document with schemas under $defs. The provided id is the id of the root document and is also used for the file name.

### `emitAllModels`

**Type:** `boolean`

When true, emit all model declarations to JSON Schema without requiring the @jsonSchema decorator.

### `emitAllRefs`

**Type:** `boolean`

When true, emit all references as json schema files, even if the referenced type does not have the `@jsonSchema` decorator or is not within a namespace with the `@jsonSchema` decorator.

## Decorators

### TypeSpec.JsonSchema

- [`@baseUri`](#@baseuri)
- [`@contains`](#@contains)
- [`@contentEncoding`](#@contentencoding)
- [`@contentMediaType`](#@contentmediatype)
- [`@contentSchema`](#@contentschema)
- [`@extension`](#@extension)
- [`@id`](#@id)
- [`@jsonSchema`](#@jsonschema)
- [`@maxContains`](#@maxcontains)
- [`@maxProperties`](#@maxproperties)
- [`@minContains`](#@mincontains)
- [`@minProperties`](#@minproperties)
- [`@multipleOf`](#@multipleof)
- [`@oneOf`](#@oneof)
- [`@prefixItems`](#@prefixitems)
- [`@uniqueItems`](#@uniqueitems)

#### `@baseUri`

Set the base URI for any schemas emitted from types within this namespace.

```typespec
@TypeSpec.JsonSchema.baseUri(baseUri: valueof string)
```

##### Target

`Namespace`

##### Parameters

| Name    | Type             | Description                                                              |
| ------- | ---------------- | ------------------------------------------------------------------------ |
| baseUri | `valueof string` | the base URI. Schema IDs inside this namespace are relative to this URI. |

#### `@contains`

Specify that the array must contain at least one instance of the provided type.
Use `@minContains` and `@maxContains` to customize how many instances to expect.

```typespec
@TypeSpec.JsonSchema.contains(value: unknown)
```

##### Target

`unknown[] | ModelProperty`

##### Parameters

| Name  | Type      | Description                      |
| ----- | --------- | -------------------------------- |
| value | `unknown` | The type the array must contain. |

#### `@contentEncoding`

Specify the encoding used for the contents of a string.

```typespec
@TypeSpec.JsonSchema.contentEncoding(value: valueof string)
```

##### Target

`string | ModelProperty`

##### Parameters

| Name  | Type             | Description |
| ----- | ---------------- | ----------- |
| value | `valueof string` | <br />      |

#### `@contentMediaType`

Specify the content type of content stored in a string.

```typespec
@TypeSpec.JsonSchema.contentMediaType(value: valueof string)
```

##### Target

`string | ModelProperty`

##### Parameters

| Name  | Type             | Description                           |
| ----- | ---------------- | ------------------------------------- |
| value | `valueof string` | the media type of the string contents |

#### `@contentSchema`

Specify the schema for the contents of a string when interpreted according to the content's
media type and encoding.

```typespec
@TypeSpec.JsonSchema.contentSchema(value: unknown)
```

##### Target

`string | ModelProperty`

##### Parameters

| Name  | Type      | Description                       |
| ----- | --------- | --------------------------------- |
| value | `unknown` | the schema of the string contents |

#### `@extension`

Specify a custom property to add to the emitted schema. Useful for adding custom keywords
and other vendor-specific extensions. Scalar values need to be specified using `typeof` to be converted to a schema.

For example, `@extension("x-schema", typeof "foo")` will emit a JSON schema value for `x-schema`,
whereas `@extension("x-schema", "foo")` will emit the raw code `"foo"`.

The value will be treated as a raw value if any of the following are true:

1. The value is a scalar value (e.g. string, number, boolean, etc.)
2. The value is wrapped in the `Json<Data>` template
3. The value is provided using the value syntax (e.g. `#{}`, `#[]`)

For example, `@extension("x-schema", { x: "value" })` will emit a JSON schema value for `x-schema`,
whereas `@extension("x-schema", #{x: "value"})` and `@extension("x-schema", Json<{x: "value"}>)`
will emit the raw JSON code `{x: "value"}`.

```typespec
@TypeSpec.JsonSchema.extension(key: valueof string, value: unknown | valueof unknown)
```

##### Target

`unknown`

##### Parameters

| Name  | Type                           | Description                                                   |
| ----- | ------------------------------ | ------------------------------------------------------------- |
| key   | `valueof string`               | the name of the keyword of vendor extension, e.g. `x-custom`. |
| value | `unknown` \| `valueof unknown` | the value of the keyword.                                     |

#### `@id`

Specify the JSON Schema id. If this model or a parent namespace has a base URI,
the provided ID will be relative to that base URI.

By default, the id will be constructed based on the declaration's name.

```typespec
@TypeSpec.JsonSchema.id(id: valueof string)
```

##### Target

`unknown`

##### Parameters

| Name | Type             | Description                                     |
| ---- | ---------------- | ----------------------------------------------- |
| id   | `valueof string` | the id of the JSON schema for this declaration. |

#### `@jsonSchema`

Add to namespaces to emit models within that namespace to JSON schema.
Add to another declaration to emit that declaration to JSON schema.

Optionally, for namespaces, you can provide a baseUri, and for other declarations,
you can provide the id.

```typespec
@TypeSpec.JsonSchema.jsonSchema(baseUri?: valueof string)
```

##### Target

`unknown`

##### Parameters

| Name    | Type             | Description                                         |
| ------- | ---------------- | --------------------------------------------------- |
| baseUri | `valueof string` | Schema IDs are interpreted as relative to this URI. |

#### `@maxContains`

Specify that the array must contain at most some number of the types provided
by the contains decorator.

```typespec
@TypeSpec.JsonSchema.maxContains(value: valueof int32)
```

##### Target

`unknown[] | ModelProperty`

##### Parameters

| Name  | Type            | Description                                            |
| ----- | --------------- | ------------------------------------------------------ |
| value | `valueof int32` | The maximum number of instances the array must contain |

#### `@maxProperties`

Specify the maximum number of properties this object can have.

```typespec
@TypeSpec.JsonSchema.maxProperties(value: valueof int32)
```

##### Target

`Record<unknown> | ModelProperty`

##### Parameters

| Name  | Type            | Description                                            |
| ----- | --------------- | ------------------------------------------------------ |
| value | `valueof int32` | The maximum number of properties this object can have. |

#### `@minContains`

Specify that the array must contain at least some number of the types provided
by the contains decorator.

```typespec
@TypeSpec.JsonSchema.minContains(value: valueof int32)
```

##### Target

`unknown[] | ModelProperty`

##### Parameters

| Name  | Type            | Description                                            |
| ----- | --------------- | ------------------------------------------------------ |
| value | `valueof int32` | The minimum number of instances the array must contain |

#### `@minProperties`

Specify the minimum number of properties this object can have.

```typespec
@TypeSpec.JsonSchema.minProperties(value: valueof int32)
```

##### Target

`Record<unknown> | ModelProperty`

##### Parameters

| Name  | Type            | Description                                            |
| ----- | --------------- | ------------------------------------------------------ |
| value | `valueof int32` | The minimum number of properties this object can have. |

#### `@multipleOf`

Specify that the numeric type must be a multiple of some numeric value.

```typespec
@TypeSpec.JsonSchema.multipleOf(value: valueof numeric)
```

##### Target

`numeric | ModelProperty`

##### Parameters

| Name  | Type              | Description                                        |
| ----- | ----------------- | -------------------------------------------------- |
| value | `valueof numeric` | The numeric type must be a multiple of this value. |

#### `@oneOf`

Specify that `oneOf` should be used instead of `anyOf` for that union.

```typespec
@TypeSpec.JsonSchema.oneOf
```

##### Target

`Union | ModelProperty`

##### Parameters

None

#### `@prefixItems`

Specify that the target array must begin with the provided types.

```typespec
@TypeSpec.JsonSchema.prefixItems(value: unknown[])
```

##### Target

`unknown[] | ModelProperty`

##### Parameters

| Name  | Type        | Description                                                                 |
| ----- | ----------- | --------------------------------------------------------------------------- |
| value | `unknown[]` | a tuple containing the types that must be present at the start of the array |

#### `@uniqueItems`

Specify that every item in the array must be unique.

```typespec
@TypeSpec.JsonSchema.uniqueItems
```

##### Target

`unknown[] | ModelProperty`

##### Parameters

None