# tags-unique

Source: https://apigenie.pl/docs/linter/swagger/rules/tags-unique

This rule checks whether the tags in the root `tags` array of a Swagger 2.0
document have unique names, comparing names case-insensitively.

## Rule Details

The Swagger 2.0 specification requires tag names to be unique. Tags whose
names differ only in letter case are just as confusing: it is unclear whether
they describe one group of operations or two.

The `tags-unique` rule reports `Tag name is not unique (<name>)` for each
duplicate. Names are compared after converting ASCII letters to lower case.
The issue normally points at the later duplicate; when the earlier tag has
only a `name` and the later one has more properties, it points at the earlier
tag instead.

The `unique-tag` check of the `swagger-validation` rule reports exact
duplicates too, but it is disabled by default in favor of this rule.

## Configuration

None.

## Examples

**Good**.

```yaml
swagger: '2.0'
info:
  title: Pet Store
  version: 1.0.0
paths: {}
tags:
  - name: pets
  - name: users
```

**Bad**. Two tags differ only in letter case.

```yaml
swagger: '2.0'
info:
  title: Pet Store
  version: 1.0.0
paths: {}
tags:
  - name: pets
    description: Operations on the pets of the shelter.
  - name: Pets
    description: Is this another tag, or a typo?
```

## Automatic fixes

When invoked with `--fix`, the rule removes a duplicate tag from the root
`tags` array when it is safe to do so:

- a duplicate that has only a `name` is removed,
- when the earlier tag has only a `name` and the later duplicate has more
  properties, the earlier tag is removed,
- a duplicate whose properties other than `name` are equal to those of the
  earlier tag is removed.

Duplicates with different descriptions, external documentation or extensions
are reported, but left for manual resolution.

## When Not to Use It

We recommend to always enable this rule.

## Compatibility

This rule is compatible with Swagger 2.0 documents. OpenAPI 3.x and AsyncAPI
documents are linted by the OpenAPI and AsyncAPI linters, which have their own
`tags-unique` rules.