# Retrieve a tag

**GET /tags/{tag}**

Read one tag by `id`, retired or not. Creator scope, and only for a
newsletter the key is bound to.



## Servers
- Production. There is no separate sandbox host.
: https://api.usecommune.com (Production. There is no separate sandbox host.
)


## Authentication methods
- Api key


## Parameters
### Headers

- **Commune-Version** (string(date))
  The contract version this request is written against, as a release date
  (`YYYY-MM-DD`). Omitting the header pins the request to the version that
  was current when the API key was issued, so an integration keeps working
  when a newer version ships. An unknown value answers `400` with
  `invalid_version`.


### Path parameters

- **tag** (string(uuid))
  The tag's `id`. A tag has no short id.


### Query parameters

- **expand** (string)
  Comma separated list of relationship paths to inline in the response.
  Unexpanded relationships are returned as a reference object carrying
  only `id` and `object`. Each operation documents the paths it accepts,
  and an unknown path answers `400`. Nested paths use a dot, for example
  `article.newsletter`.

  One accepted path is not a relationship. `?expand=content` on
  `GET /articles/{article}` adds the Markdown rendition of the body
  beside the HTML one. It is the same trade the parameter always offers,
  a fuller response for a larger one, over a property that has more than
  one representation rather than over a reference.

- **fields** (string)
  Comma separated allow list of top level properties to return on each
  object, so a client can trim a response it does not need in full. `id`
  and `object` are always returned. An unknown property name answers
  `400`. Properties omitted by an operation, such as `content` on any
  article list, cannot be brought back with `fields`.

  A trimmed body is a subset of the schema this operation declares, and a
  property that schema marks required is absent when it was not asked for.
  That is the point of the parameter, so a client that validates responses
  against the schema either sends no `fields` or relaxes `required`.



## Responses
### 200
The tag.

#### Body: application/json (object)
- **object** (string)
  Always `tag`.

- **id** (string(uuid))
  Stable identifier.

- **newsletter** (object | null)
  The newsletter the tag belongs to. A tag never spans newsletters. A
  `Ref` unless `newsletter` is named in `?expand=`.

- **name** (string)
  What the creator calls the segment. Unique among the newsletter's
  live tags, and freed for reuse once a tag is retired.

- **known_subscriber_count** (integer)
  How many currently subscribed people Commune knows of who hold this
  tag. Counted at read time from Commune's own record of the
  audience, which for a newsletter connected to an outside provider
  is a partial cache of that provider's list. Named `known_` for that
  reason: it is a floor, never the segment's true size, and it must
  not be presented as one.

- **retired** (boolean)
  `true` when the creator removed the tag but an already sent issue is
  still addressed to it. Retired tags keep their assignments, because
  the audience of a sent issue does not change retroactively. Excluded
  from the tag list unless `include_retired=true`.

- **retired_at** (string(date-time) | null)
  When the tag was retired. Null while it is live.

- **created_at** (string(date-time))
  When the tag was created.


### 400
The request was malformed: an unknown query parameter, an unparseable
cursor, an unknown `expand` path, or an unrecognised `Commune-Version`.


#### Body: application/json (object)
- **error** (object)


### 401
No API key was presented, or the key is unknown, revoked or expired.

All four answer identically, down to the wording. Saying that a key was
revoked rather than never issued confirms to whoever is holding the
string that it was once real, which a legitimate caller does not need
and a thief should not get.

#### Headers

- **WWW-Authenticate** (string)
  The authentication scheme this API accepts. Always
  `Bearer realm="Commune API"`; there is no second scheme and no
  query-parameter fallback, because a credential that can travel in a
  URL ends up in access logs and referer headers.


#### Body: application/json (object)
- **error** (object)


### 403
The key is valid but is not allowed to read this. Either it carries
public scope and the operation needs creator scope, or it is bound to a
different newsletter than the one addressed.


#### Body: application/json (object)
- **error** (object)


### 404
No such resource, or the key is not allowed to know that it exists.
Commune answers `404` rather than `403` where distinguishing the two
would leak the existence of private content.


#### Body: application/json (object)
- **error** (object)


### 429
Too many requests. Back off and retry after the interval named by the
`Retry-After` response header.

#### Headers

- **Retry-After** (integer)
  Seconds to wait before retrying.


#### Body: application/json (object)
- **error** (object)


### 500
Something failed inside Commune. The request may be retried.

#### Body: application/json (object)
- **error** (object)



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