Opening MS Project

Opening MS Project (.mpp)

Besides MS Project XML (MSPDI), Open Planner Studio can also open Microsoft Project's native .mpp file directly — no export step needed first. The reader is a self-contained TypeScript implementation of the MPP14 container format (Project 2010 through 2021). This guide explains what comes along, where the limits are, and what happens when you save a file like this.

What you'll learn here

• How to open a .mpp file, and which paths support it.
• What exactly comes along: tasks, relations, calendars, resources and assignments.
• How accurate the imported start and finish dates are, and how splitting, leveling, manual scheduling and resource contouring are accounted for.
• What happens to progress: MS Project's own resumption convention for tasks in progress.
• One known calendar limitation: work weeks (a temporary alternate weekly pattern).
• What deliberately does not come along, and what you get for an unsupported file.
• What happens when you save or re-export an opened .mpp file.

What comes along

When you open a .mpp file, Open Planner Studio reads:

• Tasks, including the hierarchy (summary tasks/subtasks) and the WBS coding.
• Relations in all four kinds (finish-to-start, start-to-start, finish-to-finish, start-to-finish), with lag — both in working days and in elapsed days, as well as percentage lag.
• Calendars: working days, working hours per day, and the concrete exception dates (days off).
• Resources, of type Work or Material. MS Project also has a Cost type, but — same as with the existing MSPDI import — it's treated as Work.
• Assignments of resources to tasks, including progress (percent complete, actual start/finish where present).

This is the same field set as the existing MS Project XML import (MSPDI), except for the limitations listed below.

For hour-based projects (tasks that MS Project schedules at hour or minute precision, or a calendar with, say, a lunch break) durations and working times come along at that precision: a 2-hour task no longer comes out as 0 days, and start/finish times keep their real time of day instead of only the date. Open Planner Studio detects this automatically, per calendar — there's nothing to turn on. See Calendars & hour planning for how hour mode works elsewhere in the app.

Opening

You open a .mpp file the exact same way as any other project file:

• File → Open (or Ctrl+O), just pick a .mpp file.
• Via recent files once you've opened one before.
• Via the AI assistant, with the planner_import_schedule tool (see the guide Connecting an AI assistant (MCP)).

The file lands in a new document — like any import — unless the active tab is still empty and unchanged.

Date accuracy

Open Planner Studio schedules an opened .mpp file using the same calendar logic as MS Project itself (working days, working hours per day, days off, and — for an hour-based project — the exact clock time). Split tasks, leveling, manually scheduled tasks and contoured (resource-driven) assignments are no longer treated as a deviating exception here — they're fully implemented behavior, see the four sections below for what that means in practice. Across the full test corpus (216 readable files / 3413 tasks, from public MPXJ and OzBuild test material to real-world projects), the start and finish date match MS Project exactly, down to the minute for an hour-based project — for every file in the corpus, with no remaining deviation. An automated test guards this: if a change would cause even a single date in the corpus to drift, the test suite fails. If you're unsure about a specific file that isn't in the corpus, check the critical tasks against MS Project after opening it.

If the file contains tasks with a split, leveled, or resource-driven schedule, a one-time informational notification appears when opening it — not a warning, since those tasks are simply scheduled correctly; the notification only tells you the file contains them.

Split tasks

A task that MS Project split into work interruptions (say, 3 days of work, a 2-day pause, then more work) is read by Open Planner Studio as such: the breaks come from the file, and the Gantt bar shows them as separate blocks joined by a thin connector line — always visible, regardless of the Task bars at interruptions setting (Settings tab, ⚙ popup, or Backstage → Settings). A work interruption is data, not a display preference; that setting only controls whether tasks without their own splits are drawn broken up on non-working days (calendar necking). The print and PDF preview show the same broken bars. Scheduling is segment-aware: remaining work keeps counting past each gap, even for a task that's already partly done.

Manually scheduled tasks

A task that was set to Manually Scheduled in MS Project keeps its own stored start and finish date in Open Planner Studio — raw, with no calendar snap and with no relation or constraint moving it; even a hard Must-Start/Finish-On pin on such a task is then a dead letter. Its successors compute normally from those dates, following the ordinary relation rules (see the guide Relations & constraints). Such tasks therefore have zero float by construction (total and free float 0) and count as critical under the default setting — they don't show ordinary float the way an automatically scheduled task does. Recalculating (F5) changes nothing about a manually scheduled task: that's the whole point.

Leveling

If MS Project gave a task a leveling delay, Open Planner Studio counts it as a real shift of the early start — down to the minute for an hour-based project, including any elapsed-time delay (which counts around the clock, not just during working hours). The delay is applied on both sides of the calculation, so the float of the task (and of tasks waiting on it) still comes out right after leveling.

Contoured assignments

If a resource assignment in MS Project got its own work window that deviates from a flat, even distribution (resource contouring, or a task spread out over a longer period than its duration alone would require), Open Planner Studio follows that window on opening: the dates come from MS Project's own stored answer, not from a plain duration calculation. What doesn't come along is the shape of that distribution itself — the rising or falling load per day within the window. Open Planner Studio doesn't yet have a contour calculation engine: a task's resource load is always spread evenly across its working days, even for an imported contoured task.

If you then edit such a task yourself — its duration, dates, assignments, or calendar — Open Planner Studio lets go of the window captured at import: the task falls back to an ordinary, continuous duration calculation without the original contour shape. The first time this happens within an open document, an informative notification appears with a link to this section; later edits in the same document don't notify again. The task's properties panel now shows whether it's still actively steered by MS Project, or whether that steering was let go after an edit — with the same link. Neither touches the file itself: the originally read distribution always stays saved, even after saving; only the DERIVED steering the engine used is let go.

Milestones: MS Project's own finish-boundary convention for finish milestones

A milestone whose Milestone kind field is set to Finish milestone (see the guide Planning & WBS, Milestone kinds section) that's linked to a predecessor via a finish-to-start relation lands on that predecessor's finish boundary itself, rather than on the next working moment after it. With an hour-based calendar (see above) that means the exact finish clock time of the predecessor — for example Tuesday 17:00, if the predecessor finishes then — instead of Wednesday 08:00. In day mode the same distinction exists, just at day granularity: the finish milestone lands on the same working day the predecessor finishes, instead of the next working day. That's MS Project's own convention for finish milestones, and Open Planner Studio follows it wherever this kind of milestone occurs, not just for a .mpp import — a finish milestone in a manually created project behaves the same way. The default value for Milestone kind is Automatic: such a milestone (and an explicit Start milestone) simply lands on the next working moment, like an ordinary task — this convention applies only to a milestone you've explicitly set to Finish milestone. An ordinary task (with its own duration) after that same predecessor always starts on the next working moment regardless.

If a milestone in the source file itself carries a duration greater than 0, the Milestone checkbox stays on, but Open Planner Studio simply schedules it as a task with that duration — see the guide Planning & WBS, Milestone kinds section.

Progress: MS Project's own resumption convention

For a task that's already partly done when you open the .mpp file, Open Planner Studio determines the resumption point of the remaining work the same way MS Project itself does: based on the actual start time plus the time already elapsed, rather than (as with a project from Primavera P6 or another format) based on the status date or the pressure from preceding tasks. You usually won't notice this — the two approaches land on the same result for most tasks — but it's why a .mpp-imported task can sometimes show a slightly different resumption point than an otherwise identical task sourced from P6 or MS Project XML. This setting is a permanent property of the project: it stays intact across Save (as IFC) and a later Open, with no toggle anywhere to see or change it.

Calendar exceptions and work weeks

Concrete, one-off exception dates in a calendar (a specific day off on a fixed date) come along just fine, and so do yearly recurring exceptions with a repeat rule — for example a holiday like Christmas that's set up in MS Project to recur automatically every year. Open Planner Studio expands such a repeat rule itself into the concrete dates within the project period; there's nothing you need to do for this. This applies both to ordinary days off and to working exceptions (a day that's normally off but explicitly marked as working in the calendar — for example a scheduled Saturday).

What remains a known limitation are work weeks — MS Project's way of assigning an alternate weekly pattern to a calendar for a given date range (for example, "starting July 1st this team also works Saturdays"). Only the standard weekly pattern and the individual exception dates come along; a temporary alternate weekly pattern doesn't. In practice this affects few files — most MS Project calendars don't use work weeks — but if you know a calendar has one, double-check it after opening, under Planning → Calendar — see the guide Calendars & hour planning.

What doesn't come along

The .mpp import is read-only: there is no .mpp export format, not even in the source project (MPXJ) the reader is based on. In addition:

• No baselines, custom fields, outline codes, subprojects or cost fields. The field set is exactly what the MSPDI import also delivers, minus baselines.
• Older .mpp formats (MPP8/9/12 — Project 98 through 2007) are recognized but not read: you get a clear error message suggesting you export the file as XML in MS Project (File → Save As → XML) and open that file instead.
• Password-protected files give the same error with the same suggestion — the contents are not decrypted.

Saving and exporting

As everywhere in Open Planner Studio, Save always writes IFC — there's no separate .mpp project format to write back to. Because an opened .mpp file (just like an opened .csv or MS Project XML) therefore gets no save target of its own, Ctrl+S on such a document is always save-as: your source file is never silently overwritten with IFC content. To bring the schedule back into MS Project, use Backstage → Export → MS Project XML — see the guide Import/export for what does and doesn't come along there.

Origin

The .mpp reader is derived from the source code and structural knowledge of MPXJ (github.com/joniles/mpxj, Jon Iles et al.), a Java library under LGPL-2.1 — just like Open Planner Studio itself is open source under LGPL-3.0.

Further reading

• What each export and import format does and doesn't carry: Import/export.
• Checking working days, hours and holidays after opening: Calendars & hour planning.