Build a simple Gantt chart maker for one planner

The data behind the bars

Task: A name, a start date, and a duration in working days (or an end date), with an optional owner and colour.
Group: A phase that holds tasks (Discovery, Design, Build, Launch), drawn as a summary bar spanning its tasks.
Dependency: Finish-to-start is the common one: B can't start until A is done. Optionally a lag ("two days after"). Other types (start-to-start, finish-to-finish) are rarely needed in a simple tool.
Milestone: A zero-length point such as sign-off or launch day, drawn as a diamond.
Calendar: Working days per week and holidays to skip, so a five-day task starting on Thursday ends the next Wednesday.
Progress: Percentage complete per task, drawn as a fill inside the bar.

When one date moves

The reason to use a project timeline maker instead of drawing boxes in a slide is that it reflows. Move a task or lengthen it, and every task that depends on it shifts, skipping weekends and holidays, along with the summary bars and the end date. Two details make that trustworthy:

Circular dependencies are refused. If A depends on B and B on A, the app should say so and not save the link.
Pinned dates. A task fixed to a date (a venue booking, a contract deadline) shouldn't be pushed; instead, a conflict warning appears if its predecessors now finish late.
Critical path. The chain of tasks where any delay moves the end date, highlighted. It tells you where to watch closely, and it's straightforward to compute for a project of this size.
Baseline. A saved copy of the original plan drawn faintly behind the current bars, so slippage is visible.

Most editing happens in a table on the left (name, start, duration, depends on) with the chart on the right, and also by dragging bar ends on the chart. A zoom from days to weeks to months keeps long projects readable. Everything is saved in the browser on your device.

To share, there are two routes that need no network. Printing uses a print layout that fits the timeline to landscape pages, and the browser's print dialog can save it as a PDF. An image download draws the chart to a PNG file the app hands to your browser, ready to drop into an email, a proposal or a slide.

Describing it to Anticode

"A simple Gantt chart maker for planning website projects for clients. Tasks in phases with start, duration in working days, owner and progress; finish-to-start dependencies with optional lag; milestones; a Monday-to-Friday calendar with holidays. Moving a task reflows its dependents; pinned tasks warn instead of moving. Highlight the critical path and show a saved baseline. Table on the left, chart on the right, drag to resize bars, zoom days to months. Print to landscape and download as PNG. Saves on this device with JSON export. Technical, precise design."

For an agency, the timeline often goes into a proposal; see the website proposal workflow and the proposal generator. For tracking day-to-day work rather than dates, a Kanban board app fits better.

What it isn't

This is a planning and communication tool for one person on one device. It isn't a team project management system, and the sandbox it runs in rules out the parts that would make it one:

No shared editing or live updates. Team members can't update their own tasks; you'd collect updates and enter them.
No accounts or permissions. Anyone with the link to the published app gets their own empty copy, not your plan.
No resource levelling. It shows owners but doesn't balance workloads across people.
No integrations with issue trackers, calendars or time tracking.
Not for large programmes. Hundreds of interlinked tasks across teams belong in dedicated software. If you need a multi-user planner of your own, the project management prototype page and the Next.js export are the route a developer would take.

Questions people ask

Can a Gantt chart maker like this import from Excel?

Ask for a paste or CSV import with columns for name, start, duration and dependencies. The tasks then live on this device.

Can I share the live chart with a client?

Not live. Send an image or a PDF. If they open the app link, they see their own empty copy.

Does it count weekends?

Only if you want it to. Set the working days and holidays, and durations are counted in working days.