> ## 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. # Add a comment or reply > Add a Markdown comment or a nested reply using `parentId`. Top-level comments have depth zero; replies support at most three nested levels. Mention with `@email`, `@[Name](user:UUID)`, or `mentionIds`. Reuse the `Idempotency-Key` header on retries. Write access: a member/administrator with a write-enabled credential, or an authorized signed-in user. Add a Markdown comment or a nested reply using `parentId`. Top-level comments have depth zero; replies support at most three nested levels. Mention with `@email`, `@[Name](user:UUID)`, or `mentionIds`. Reuse the `Idempotency-Key` header on retries. Body is nonempty and at most 10,000 characters. Supports `@email`, `user:UUID` links and `mentionIds`. Root depth is zero; a fourth reply level returns 400 `COMMENT_DEPTH_LIMIT`. Comments advance board activity but do not produce activity-table rows. MCP clients can use [`add_comment`](https://www.mill.fyi/mcp-reference/add_comment) for this operation. [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 POST /api/tasks/{taskId}/comments 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/tasks/{taskId}/comments: post: tags: - Comments and activity summary: Add a comment or reply description: >- Add a Markdown comment or a nested reply using `parentId`. Top-level comments have depth zero; replies support at most three nested levels. Mention with `@email`, `@[Name](user:UUID)`, or `mentionIds`. Reuse the `Idempotency-Key` header on retries. Body is nonempty and at most 10,000 characters. Supports `@email`, `user:UUID` links and `mentionIds`. Root depth is zero; a fourth reply level returns 400 `COMMENT_DEPTH_LIMIT`. Comments advance board activity but do not produce activity-table rows. Write access: a member/administrator with a write-enabled credential, or an authorized signed-in user. operationId: post_api_tasks_by_taskId_comments parameters: - name: taskId in: path required: true schema: type: string format: uuid description: >- The taskId 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: parentId: 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)$ body: type: string minLength: 1 maxLength: 10000 mentionIds: default: [] maxItems: 50 type: array items: 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)$ required: - body additionalProperties: false example: parentId: 33333333-3333-4333-8333-333333333333 body: The isolated restore passed. responses: '201': description: >- Successful response. Examples are illustrative; field values vary by record. content: application/json: schema: type: object properties: comment: type: object properties: id: type: string taskId: type: string parentId: type: string replyCount: type: integer authorId: type: string authorKind: type: string authorName: type: string body: type: string version: type: integer createdAt: type: string updatedAt: 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: comment: id: 88888888-8888-4888-8888-888888888888 taskId: 22222222-2222-4222-8222-222222222222 parentId: 33333333-3333-4333-8333-333333333333 replyCount: 0 authorId: 66666666-6666-4666-8666-666666666666 authorKind: human authorName: Alex Morgan body: The isolated restore passed. version: 1 createdAt: '2027-01-18T09:30:00.000Z' updatedAt: '2027-01-18T09:30:00.000Z' 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.