Free offline Gantt chart tool — your data never leaves your browser

A security engineer built a personal Gantt chart tool after Excel became too slow and fragile beyond 300 rows. The standout feature is that project data never leaves your device. The tool enforces a Content Security Policy (CSP) that blocks all outbound requests at the browser level, so nothing is sent to any external server.

It works from a local file with no internet connection at all, and you can open your browser's developer tools to watch the network tab and confirm zero data leaves after the page loads. Feature-wise, it works like a spreadsheet grid linked to the chart: paste in rows, drag to reorder, and group tasks into a hierarchy. Task dependencies are set with simple text like "start 3 days after the task above finishes," and the tool automatically accounts for weekends and holidays.

Edits work both ways — double-click the chart to add a task, or type in the grid. There is no account, no login, no usage tracking, and the code is open source under the MIT license, meaning anyone can use or modify it for free.