> ## Documentation Index > Fetch the complete documentation index at: https://www.mill.fyi/llms.txt > Use this file to discover all available pages before exploring further. # Update multiple tasks > Atomically updates 1–100 distinct tasks in this board. Every task needs its current version. Stale versions return 409; unavailable tasks return 404; either failure rolls back every selected change. Assignees must be active members, null unassigns. Dates accept null to clear. Actual status changes reset `statusChangedAt`; unrelated edits preserve it. Assignments respect notification preferences. Omitted fields are preserved. Write access: a member/administrator with a write-enabled credential, or an authorized signed-in user. Atomically updates 1–100 distinct tasks in this board. Every task needs its current version. Stale versions return 409; unavailable tasks return 404; either failure rolls back every selected change. Assignees must be active members, null unassigns. Dates accept null to clear. Actual status changes reset `statusChangedAt`; unrelated edits preserve it. Assignments respect notification preferences. Omitted fields are preserved. [Request conventions](https://www.mill.fyi/api-reference/overview.md) · [API keys](https://www.mill.fyi/api-keys.md) · [MCP connections](https://www.mill.fyi/mcp-connections.md) ## OpenAPI ````yaml api-reference/openapi.json PATCH /api/boards/{boardId}/tasks/bulk openapi: 3.1.0 info: title: Mill HTTP API version: 1.0.6 description: >- All registered task-board, account, OAuth, MCP transport and health operations. MCP tool schemas come from runtime validators; account operations follow their server handlers. Example data is fictional. Generation imports routes without issuing requests or connecting to a database. servers: - url: https://mill-api.example.com security: [] paths: /api/boards/{boardId}/tasks/bulk: patch: tags: - Tasks summary: Update multiple tasks description: >- Atomically updates 1–100 distinct tasks in this board. Every task needs its current version. Stale versions return 409; unavailable tasks return 404; either failure rolls back every selected change. Assignees must be active members, null unassigns. Dates accept null to clear. Actual status changes reset `statusChangedAt`; unrelated edits preserve it. Assignments respect notification preferences. Omitted fields are preserved. Write access: a member/administrator with a write-enabled credential, or an authorized signed-in user. operationId: patch_api_boards_by_boardId_tasks_bulk parameters: - name: boardId in: path required: true schema: type: string format: uuid description: >- The boardId from the corresponding list, record or authorization response. - name: Origin in: header required: false schema: type: string format: uri description: >- The exact configured Mill UI origin. Required for browser mutations carrying session cookies. - name: Idempotency-Key in: header required: false schema: type: string minLength: 8 maxLength: 128 pattern: ^[A-Za-z0-9._:-]+$ description: >- Reuse the same key and exact request bytes for retries of one logical mutation; different content conflicts. requestBody: required: true content: application/json: schema: type: object properties: tasks: minItems: 1 maxItems: 100 type: array items: type: object properties: id: type: string format: uuid pattern: >- ^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$ version: type: integer exclusiveMinimum: 0 maximum: 9007199254740991 required: - id - version additionalProperties: false changes: type: object properties: status: type: string enum: - backlog - todo - in_progress - in_review - done - wont_do assigneeId: anyOf: - type: string format: uuid pattern: >- ^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$ - type: 'null' priority: type: string enum: - none - low - medium - high - urgent startDate: anyOf: - type: string format: date pattern: >- ^(?:(?:\d\d[2468][048]|\d\d[13579][26]|\d\d0[48]|[02468][048]00|[13579][26]00)-02-29|\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\d|30)|(?:02)-(?:0[1-9]|1\d|2[0-8])))$ - type: 'null' dueDate: anyOf: - type: string format: date pattern: >- ^(?:(?:\d\d[2468][048]|\d\d[13579][26]|\d\d0[48]|[02468][048]00|[13579][26]00)-02-29|\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\d|30)|(?:02)-(?:0[1-9]|1\d|2[0-8])))$ - type: 'null' additionalProperties: false required: - tasks - changes additionalProperties: false example: tasks: - id: 22222222-2222-4222-8222-222222222222 version: 1 changes: assigneeId: null responses: '200': description: >- Successful response. Examples are illustrative; field values vary by record. content: application/json: schema: type: object properties: items: type: array items: type: object properties: id: type: string boardId: type: string identifier: type: string title: type: string description: type: string acceptanceCriteria: type: string type: type: string status: type: string priority: type: string assigneeId: type: - string - 'null' startDate: type: string dueDate: type: string version: type: integer statusChangedAt: type: string createdAt: type: string updatedAt: type: string createdBy: type: string additionalProperties: true additionalProperties: true description: >- Illustrative response shape. Fields can be absent in alternate successful flows; see the operation description and example. example: items: - id: 22222222-2222-4222-8222-222222222222 boardId: 11111111-1111-4111-8111-111111111111 identifier: ENG-1 title: Verify database restore description: Restore a recent backup into an isolated database. acceptanceCriteria: |- - Confirm task and comment counts match - Record the result type: task status: todo priority: high assigneeId: null startDate: '2027-01-18' dueDate: '2027-01-20' version: 2 statusChangedAt: '2027-01-18T09:30:00.000Z' createdAt: '2027-01-18T09:30:00.000Z' updatedAt: '2027-01-18T09:30:00.000Z' createdBy: 66666666-6666-4666-8666-666666666666 default: description: >- Request failure. Inspect code, message and requestId; respect Retry-After on HTTP 429. content: application/json: schema: $ref: '#/components/schemas/Error' security: - bearerAuth: [] - sessionCookie: [] components: schemas: Error: type: object required: - error properties: error: type: object required: - code - message - requestId properties: code: type: string message: type: string requestId: type: string securitySchemes: bearerAuth: type: http scheme: bearer description: Personal or team Mill REST API key sessionCookie: type: apiKey in: cookie name: mill_session description: >- Signed-in human browser session; mutation requests also need the exact UI Origin ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.