# POST /api/v2/work-items/{work_item}/links

Link a work item to another

- MCP id: work-items.links.store
- Scope: api:write:project_management
- Permission: project_management::manage_work_items
- Rate cost: 1 unit, write bucket. A write costs the same whatever `view` you ask for.
- Cache-Control: private, no-store

Creates a link from the work item in the path to another work item in the same project, and returns it with a `Location` header pointing at the flat item path.

The body is exactly `link_type` and `target_work_item_id`: the source comes from the path, so `source_work_item_id` is not accepted, and `created_by` is the authenticated caller. To create the inverse of a relationship ("this item is blocked by ACM-9"), post to ACM-9's own collection instead: `POST work-items/ACM-9/links` with `link_type=blocks` and this item as the target stores the identical row, which both ends then read from their own side. Three refusals mirror plnnrly: a work item in another project is refused exactly as a nonexistent one is, linking an item to itself is `422` `unprocessable-relationship`, and repeating an existing (source, target, `link_type`) triple is `409` `duplicate-resource`.

## Parameters
- work_item (integer or string, path): The WorkItem's numeric id. Or its issue_key, matching `[A-Z][A-Z0-9]*-[0-9]+`.
- view (string, optional): Which field set to render.
- X-Request-Id (header, optional): A correlation id of your own. It is recorded in our logs next to the server's request id but never returned: the response header always carries the server's id. A value that does not match the pattern is discarded silently, never rejected.
- Idempotency-Key (header, optional): A caller-chosen key that makes this POST safe to retry. Replaying it returns the original response with Idempotency-Replayed: true.

## Request body
- link_type (string, required): The relationship, stored from the source item's point of view: `blocks`, `clones`, `duplicates`, `merged_into`, `causes`, `relates_to` or `split_to`. Only `relates_to` is symmetric.
- target_work_item_id (integer → WorkItem.id, required): Work item the link points at. Always in the same project as the source.

Unknown keys are refused with `422` validation-failed, naming the key.

## Response 201
- id (integer, required): Unique identifier.
- source_work_item_id (integer, required): Work item the link points away from. On a link created through `POST work-items/{work_item}/links` this is always the work item named in the path.
- target_work_item_id (integer, required): Work item the link points at. Always in the same project as the source.
- link_type (string, required): The relationship, stored from the source item's point of view: `blocks`, `clones`, `duplicates`, `merged_into`, `causes`, `relates_to` or `split_to`. Only `relates_to` is symmetric.
- created_by (integer or null, required, server-assigned): User who created the link, or `null` where that account has since been deleted. Resolve it with `GET /api/v2/users/{user}`; it is not includable.
- created_at (timestamp (YYYY-MM-DDThh:mm:ssZ), required): Creation timestamp.
- updated_at (timestamp (YYYY-MM-DDThh:mm:ssZ), required): Last-write timestamp; use for incremental sync.
- direction (string, required): Which way this link points relative to the work item you asked about: `forward` when that item is the source, `inverse` when it is the target. On the flat `GET work-item-links/{work_item_link}` there is no work item in the path, so the link is read on its own terms and this is always `forward`.
- relationship (string, required): The relationship in words, from the point of view of the work item you asked about: `blocks` from the source end, `is blocked by` from the target end. Always in English: the API pins the locale.
- source_work_item (Ref or WorkItemSummary, required): Work item the link points away from.
- target_work_item (Ref or WorkItemSummary, required): Work item the link points at.
- links (WorkItemLinkLinks, required)
  - self (url, required): The canonical URI of this record.

## Errors
- 403 forbidden-by-policy | insufficient-permission | insufficient-token-scope: Forbidden.
- 409 duplicate-resource | idempotency-key-in-flight | idempotency-key-reused: Conflict.
- 415 unsupported-media-type: Unsupported media type.
- 422 unprocessable-relationship | validation-failed: Unprocessable content.
- 400 idempotency-key-required | invalid-cursor | invalid-query-parameter | malformed-request | unsupported-parameter: Bad request.
- 401 token-expired | unauthenticated: Unauthenticated.
- 404 endpoint-not-found | resource-not-found: Not found.
- 406 not-acceptable: Not acceptable.
- 429 rate-limit-exceeded: Too many requests.
- 500 internal-error: Server error.
- 503 tenant-unavailable: Service unavailable.

## Example
```bash
curl -X POST \
  'https://<your-url>/api/v2/work-items/1/links' \
  -H 'Authorization: Bearer <token>' \
  -H 'Accept: application/json' \
  -H 'Content-Type: application/json' \
  -H 'Idempotency-Key: <key>' \
  -d '{
    "link_type": "blocks",
    "target_work_item_id": 1
  }'
```