[Canonical page](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/task-data/>)
[Full documentation index](<https://docs.dhtmlx.com/planning-engine/llms.txt>)


# TaskData

One task as the engine imports it: id, place in the hierarchy, dates, duration, scheduling flags and leveling inputs. It appears as an entry of [`ProjectData`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/project-data.md>)`.tasks` and of `tasks.add` in a [`SchedulingChanges`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/scheduling-changes.md>) set. To change an existing task, send a [`TaskUpdate`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/task-update.md>) instead.

Field names are snake_case and `type` is spelled without a prefix. A record must be a JSON object. Unknown fields are ignored, so task objects with extra UI properties can be sent as they are. `null` in any optional field reads as the default. See [Wire format](<https://docs.dhtmlx.com/planning-engine/wasm/wire-format.md#omitted-null-and-unknown-fields>).

## Fields

| Field | Type | Required | Default | Description |
|---|---|---|---|---|
| `id` | [`Id`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#id>) | yes | - | Task id. Unique among tasks; `1` and `"1"` are the same id |
| `parent` | [`Id`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#id>) \| `null` | no | no parent | Id of the parent summary. `""` and a value equal to `config.root_id` also mean no parent |
| `type` | `"task"` \| `"summary"` \| `"project"` \| `"milestone"` | no | `"task"` | `"task"` (leaf), `"summary"`, `"project"` (input alias of `"summary"`) or `"milestone"` |
| `start_date` | [`DateValue`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#datevalue>) \| `null` | no | absent | Start date |
| `end_date` | [`DateValue`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#datevalue>) \| `null` | no | absent | End date. Can't be before `start_date` |
| `duration` | `number` \| `null` | no | absent | Working time in `duration_unit`. Fractional values are allowed; negative ones are rejected |
| `duration_unit` | [`TimeUnit`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#timeunit>) \| `null` | no | `config.duration_unit` | Unit of `duration`, `leveling_delay` and `pauses`: `"minute"`, `"hour"` or `"day"` |
| `constraint_type` | [`ConstraintType`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#constrainttype>) \| `null` | no | none | `"asap"`, `"alap"`, `"snet"`, `"snlt"`, `"fnet"`, `"fnlt"`, `"mso"` or `"mfo"`. Acts only when `config.apply_constraints` is `true` |
| `constraint_date` | [`DateValue`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#datevalue>) \| `null` | no | absent | Date of a dated constraint. Required when `constraint_type` is anything other than `"asap"` or `"alap"` |
| `auto_scheduling` | `boolean` \| `null` | no | `true` | `false` fixes the task: it's never moved, but its links still push successors |
| `unscheduled` | `boolean` \| `null` | no | `false` | `true` leaves the task and its descendants out of the plan; no dates are needed |
| `progress` | `number` \| `null` | no | `0` | Completion from `0` to `1`. With `config.use_progress`, `1` marks the task completed and fixed |
| `priority` | `number` \| `null` | no | `500` | Leveling priority, a whole number from `0` to `1000`. `1000` means the task is never leveled |
| `leveling_delay` | `number` \| `null` | no | `0` | Elapsed time added before the task's driven start, in `duration_unit` (a day is 24 hours). Not negative |
| `pauses` | [`Pause`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#pause>)`[]` \| `null` | no | `[]` | Leveling splits, sorted by `at` and non-overlapping. Ignored on summaries, milestones and unscheduled tasks |
| `calendar_id` | [`Id`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/common.md#id>) \| `null` | no | `"global"` calendar | Calendar the task works on. Must name a calendar in `ProjectData.calendars`. With `calendar_mode: "task-inherited"`, a task without one uses its nearest ancestor's |

Which dates a task needs depends on `type`:

- `"task"`: two of `start_date`, `end_date` and `duration`. The third is derived. If all three are sent, they must agree on the task's calendar.
- `"summary"`: both dates or neither. Its span is rolled up from its children, so `start_date` + `duration` is rejected. A summary without dates needs a dated child.
- `"milestone"`: `start_date` or `end_date`. Its duration is `0`.

`leveling_delay` and `pauses` are normally written by [`level`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-level.md>). See [Leveling resources](<https://docs.dhtmlx.com/planning-engine/wasm/resources-and-assignment/leveling-resources.md#delays-and-pauses>) before setting them by hand.

The validation errors these fields produce, and their paths, are listed in [Project data](<https://docs.dhtmlx.com/planning-engine/wasm/scheduling/project-data.md#validation-rules>).

:::note
A `priority` outside 0..1000 or a malformed hour range fails the whole call with a `validation` error that has no `path`. In `apply`, this means no operation from that change set is applied.
:::

## Used by

- [`schedule`](<https://docs.dhtmlx.com/planning-engine/wasm/api/schedule.md>), [`JsonProject.solve`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-solve.md>) and [`JsonProject.analyze`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-analyze.md>): in `ProjectData.tasks`
- [`JsonProject.apply`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-apply.md>) and [`JsonProject.preview`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-preview.md>): in `SchedulingChanges.tasks.add`
- [`JsonProject.evaluate`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md>): in a candidate's `changes.tasks.add`

## Example

A summary with two leaf tasks, a milestone and a fixed task measured in hours:

```json
[
  { "id": "phase", "type": "summary" },
  { "id": "design", "parent": "phase", "start_date": "2026-08-10 08:00", "duration": 3 },
  { "id": "build", "parent": "phase", "start_date": "2026-08-13 08:00", "end_date": "2026-08-20 08:00", "priority": 800 },
  { "id": "release", "type": "milestone", "start_date": "2026-08-20 08:00" },
  {
    "id": "audit",
    "start_date": "2026-08-10 08:00",
    "duration": 12,
    "duration_unit": "hour",
    "auto_scheduling": false
  }
]
```

## Related

- [`ProjectData`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/project-data.md>) - the `tasks` array
- [`TaskUpdate`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/task-update.md>) - edits to an existing task
- [Project data](<https://docs.dhtmlx.com/planning-engine/wasm/scheduling/project-data.md>) - task dates and validation rules
- [Links, constraints and summaries](<https://docs.dhtmlx.com/planning-engine/wasm/scheduling/links-constraints-summaries.md>) - constraints, summaries and fixed tasks
- [Leveling Resources](<https://docs.dhtmlx.com/planning-engine/wasm/resources-and-assignment/leveling-resources.md>) - `leveling_delay`, `pauses` and `priority`