# Link a card to something

`POST https://evohub.io/api/v1/board/cards/{cardID}/links`

Part of the [Board API](https://docs.evohub.io/board.md) reference · operationId `addCardLink`.

Links the card to a thing in another product, such as an incident or
a monitor. `service` and `entity_type` are lowercase identifiers
(letters, digits, and single `-`, `_` or `.` between them, at most 100
characters); `entity_id` is required (at most 100); `url` must be
`http://` or `https://` (at most 2,048); `title` is optional (at most
200).

A card holds one link per `service`, `entity_type` and `entity_id`:
linking the same thing again updates its `url` and `title`.

Requires the `board:card:write` scope.

## Authorization

Any one of:

- `bearerKey`
- `headerKey`

Where:

- `bearerKey`: HTTP Bearer — An EvoHub API key (`evohub_…`) as a bearer token.
- `headerKey`: API key in the header `X-API-Key` — An EvoHub API key (`evohub_…`).

## Path parameters

- `cardID` (string, required, example `crd_9f2e4d6c8b0a1e3f5d7c9b1a3e5f7d90`): The card's ID.

## Request body (required)

Content type: `application/json`

Type: `object`

- `service` (string, required, max length 100)
- `entity_type` (string, required, max length 100)
- `entity_id` (string, required, max length 100)
- `url` (string (uri), required, max length 2048)
- `title` (string, max length 200)

## Responses

### 201 — The card is linked.

Content type: `application/json`

Type: `object`

- `data` (object)
  - `link` (Link)
    - `id` (string)
    - `card_id` (string)
    - `service` (string, example `oncall`)
    - `entity_type` (string, example `incident`)
    - `entity_id` (string)
    - `url` (string)
    - `title` (string)
    - `created_by` (string)
    - `created_at` (string (date-time))

### 400 — The body is not JSON for this endpoint, or carries a field it does not know (`INVALID_BODY`), or a field breaks a rule (`VALIDATION_ERROR`; the message says which).

Content type: `application/json`

Type: `Error`

- `error` (object, required)
  - `code` (string, required, example `NOT_FOUND`)
  - `message` (string, required, example `not found`)
  - `request_id` (string)

### 401 — No API key was sent, or it is unknown, revoked or expired (`UNAUTHORIZED`).

Content type: `application/json`

Type: `Error`

- `error` (object, required)
  - `code` (string, required, example `NOT_FOUND`)
  - `message` (string, required, example `not found`)
  - `request_id` (string)

### 403 — The key lacks the scope this endpoint needs (`FORBIDDEN`).

Content type: `application/json`

Type: `Error`

- `error` (object, required)
  - `code` (string, required, example `NOT_FOUND`)
  - `message` (string, required, example `not found`)
  - `request_id` (string)

### 404 — It does not exist, or it is on a board the caller cannot see (`NOT_FOUND`).

Content type: `application/json`

Type: `Error`

- `error` (object, required)
  - `code` (string, required, example `NOT_FOUND`)
  - `message` (string, required, example `not found`)
  - `request_id` (string)

### 429 — Too many requests (`RATE_LIMITED`). Wait for `Retry-After` seconds.

Headers:

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

Content type: `application/json`

Type: `Error`

- `error` (object, required)
  - `code` (string, required, example `NOT_FOUND`)
  - `message` (string, required, example `not found`)
  - `request_id` (string)

### 500 — Something went wrong on EvoHub's side (`INTERNAL_ERROR`). Retry later.

Content type: `application/json`

Type: `Error`

- `error` (object, required)
  - `code` (string, required, example `NOT_FOUND`)
  - `message` (string, required, example `not found`)
  - `request_id` (string)

## Example request

```bash
curl -X POST 'https://evohub.io/api/v1/board/cards/crd_9f2e4d6c8b0a1e3f5d7c9b1a3e5f7d90/links' \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer <TOKEN>' \
  -d '{
  "url": "https://evohub.io/uptime/monitors/mon_8c1d0b52-6f3e-4a7d-9b21-0e5c4f7a3d19",
  "title": "Checkout API",
  "service": "uptime",
  "entity_id": "mon_8c1d0b52-6f3e-4a7d-9b21-0e5c4f7a3d19",
  "entity_type": "monitor"
}'
```