# standard-media-types

Source: https://apigenie.pl/docs/linter/asyncapi/rules/standard-media-types

This rule checks whether messages use only standard media types.

## Rule Details

Using non-standard media types can lead to interoperability issues:
consumers and tools may not know how to decode the messages.

The `standard-media-types` rule checks the following fields of an AsyncAPI
document:

- the root `defaultContentType`,
- the `contentType` of every message,
- the `contentType` of every message trait.

For every value that is not a recognized media type, the rule reports
`Non-standard media type is used (<value>)`. Media type parameters (such as
`; charset=utf-8`) are allowed and ignored.

A media type is recognized when it has the `type/subtype` form and its
subtype is one of the well-known subtypes, such as `json`, `xml`, `plain`,
`octet-stream`, `problem+json`, `vnd.api+json` or `x-www-form-urlencoded`.
Note that some media types commonly used with message brokers, for example
`application/vnd.apache.avro+json`, `application/x-protobuf` or
`application/cloudevents+json`, are not currently recognized.

## Configuration

None.

## Examples

**Good**.

```yaml
asyncapi: 3.0.0
info:
  title: Pet Events
  version: 1.0.0
defaultContentType: application/json
channels:
  petAdopted:
    address: pets.adopted
    messages:
      petAdopted:
        contentType: application/json; charset=utf-8
        payload:
          type: object
```

**Bad**. `json` is not a media type, and `application/pet` uses a subtype
that is not registered.

```yaml
asyncapi: 3.0.0
info:
  title: Pet Events
  version: 1.0.0
defaultContentType: json
channels:
  petAdopted:
    address: pets.adopted
    messages:
      petAdopted:
        contentType: application/pet
        payload:
          type: object
```

## When Not to Use It

You may disable this rule if your messages use vendor-specific media types,
or binary serialization formats that the rule does not recognize.

## Compatibility

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