# parameter-description-defined

Source: https://apigenie.pl/docs/linter/asyncapi/rules/parameter-description-defined

This rule checks whether every channel parameter of an AsyncAPI document has a
meaningful description.

## Rule Details

Channel parameters are the variable parts of channel addresses, such as
`userId` in `users.{userId}.signedUp`. A description explains what the
parameter identifies and which values it may take.

The `parameter-description-defined` rule checks the entries of the
`parameters` map of every channel (in the root `channels` map and in
`components/channels`), as well as the entries of `components/parameters`.
References are checked where the referenced parameter is defined.

The rule reports `Parameter '<name>' has no meaningful description` for every
parameter whose description:

- is missing, empty or blank,
- is shorter than the configured minimal length,
- is a placeholder: `TODO`, `FIXME` or `TBD` (case-insensitive).

## Configuration

The configuration block is a positive integer: the minimal length of a
description, in characters. The default value is `10`.

**Configuration Example**. The following configuration requires parameter
descriptions to be at least 20 characters long.

```yaml
version: "1.0"
commands:
  lint:
    asyncapi:
      rules:
        parameter-description-defined: [warning, 20]
```

## Examples

**Good**.

```yaml
asyncapi: 3.0.0
info:
  title: User Events
  version: 1.0.0
channels:
  userSignedUp:
    address: users.{userId}.signedUp
    parameters:
      userId:
        description: Identifier of the user who signed up.
```

**Bad**. The first parameter has no description at all, the second one has
a placeholder.

```yaml
asyncapi: 3.0.0
info:
  title: User Events
  version: 1.0.0
channels:
  userSignedUp:
    address: users.{region}.{userId}.signedUp
    parameters:
      region: {}
      userId:
        description: TODO
```

## When Not to Use It

We recommend to always enable this rule.

## Compatibility

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