# schema-no-additional-properties

Source: https://apigenie.pl/docs/linter/asyncapi/rules/schema-no-additional-properties

This rule ensures that object schemas explicitly disallow additional
properties.

## Rule Details

By default, JSON Schema allows objects to contain properties that are not
listed in `properties`. Messages containing unexpected properties are then
considered valid, which hides typos and makes it easy to leak data that was
never meant to be published.

The `schema-no-additional-properties` rule reports
`Object schema does not disable additional properties` for every schema of
type `object` that does not have `additionalProperties: false`.

## Configuration

None.

## Examples

**Good**.

```yaml
asyncapi: 3.0.0
info:
  title: User Events
  version: 1.0.0
components:
  schemas:
    UserSignedUp:
      type: object
      properties:
        user_id:
          type: string
      additionalProperties: false
```

**Bad**.

```yaml
asyncapi: 3.0.0
info:
  title: User Events
  version: 1.0.0
components:
  schemas:
    UserSignedUp:
      type: object
      properties:
        user_id:
          type: string
```

## Automatic fixes

When invoked with `--fix`, this rule sets `additionalProperties: false` on
every reported schema, replacing any other value of `additionalProperties`.

## When Not to Use It

You may disable this rule if your messages are designed to be extensible, or
if consumers are expected to ignore unknown properties.

## Compatibility

This rule is compatible with AsyncAPI 3.x documents. AsyncAPI 2.x documents
are rejected by the reader and are not linted.