Ganttly Project Timeline

Gantt charts and critical path schedules from a task list, with CSV, calendar and SVG exports.

Ganttly Project Timeline is a Gantt chart maker and critical path calculator for ChatGPT. Give it a task list with durations and dependencies and a start date, and it computes the schedule with the critical path method: early start, early finish, late start, late finish, total float and free float for every task, the critical path, milestones and the project end date. Durations count business days, skipping weekends and the public holidays of a country you choose, or plain calendar days. The interactive Gantt chart shows bars, dependency arrows, the critical path, milestones and a today line, and you can test what happens if a task slips. Downloads: a CSV schedule, an .ics calendar of milestones and task starts, and an SVG Gantt chart image.

What it does

Critical path method (CPM): forward and backward pass with early and late dates, total float and free float
Business days with weekends and public holidays for 200+ countries, plus your own days off; or calendar days
Finish-to-start dependencies with lags and leads, start-no-earlier-than dates and zero-length milestones
Clear errors for dependency loops and tasks that do not exist
Interactive Gantt chart with dependency arrows, critical path, milestones, today line and a what-if slip test
CSV schedule, .ics calendar of milestones and task starts, and an SVG Gantt chart image

Try asking ChatGPT

“Gantt chart starting 2026-11-02: Design 5d, Build 10d after Design, Test 4d after Build, Docs 3d after Design, Launch after Test and Docs”

“Find the critical path: A 3d; B 5d after A; C 2d after A; D 4d after B and C. Start 2026-11-02”

“If Build slips 5 days, when do we finish? Design 5d, Build 10d after Design, Test 4d after Build, start 2026-11-02”

Limitations

Finish-to-start dependencies only (with lags and leads); start-to-start and finish-to-finish links are not modelled
Schedules in whole days; resource levelling, hours, costs and progress tracking are not included
Public holidays come from the open-source date-holidays data; company closures need non_working_dates
Plans are not saved or synced with project tools; up to 150 tasks per plan

Connect

Install Ganttly Project Timeline from the ChatGPT plugin directory. Developers can connect the MCP endpoint directly: https://gantt-timeline.zovo.one/mcp