---

name: gantt-planner description: "Generate interactive HTML Gantt charts with Critical Path Method (CPM) analysis from task lists and dependencies, highlighting the critical path and calculating float times. Use when the user asks to create a Gantt chart, schedule project tasks, analyze the critical path, visualize dependencies, or mentions project timelines, milestones, or task scheduling." license: MIT

gantt-planner -- Interactive Gantt Chart & Critical Path Analysis

Automatically performs Critical Path Method (CPM) analysis on task lists and their dependencies, generating interactive HTML Gantt charts. Supports zooming, critical path filtering, hover details, and dependency arrow visualization.

Quick Start

Simplest usage — pass JSON directly:

python3 scripts/gantt_generator.py --json '{
  "project": "New Product Launch",
  "tasks": [
    {"id": "T1", "name": "Requirements Analysis", "duration": 5, "dependencies": []},
    {"id": "T2", "name": "UI Design", "duration": 4, "dependencies": ["T1"]},
    {"id": "T3", "name": "Backend Development", "duration": 8, "dependencies": ["T1"]},
    {"id": "T4", "name": "Frontend Development", "duration": 6, "dependencies": ["T2"]},
    {"id": "T5", "name": "Integration Testing", "duration": 3, "dependencies": ["T3", "T4"]},
    {"id": "T6", "name": "Deployment", "duration": 2, "dependencies": ["T5"]}
  ]
}' --output gantt.html

Read from a file with a specified start date:

python3 scripts/gantt_generator.py --file tasks.json --start-date 2026-05-01 --output gantt.html

Methodology: Critical Path Method (CPM)

Core Concepts

Term	Abbreviation	Meaning
Earliest Start	ES	The earliest point at which a task can begin
Earliest Finish	EF	The earliest point at which a task can be completed (ES + Duration)
Latest Start	LS	The latest a task can start without delaying the project
Latest Finish	LF	The latest a task can finish without delaying the project
Total Float	TF	LS − ES; the number of days a task can be delayed
Critical Path	—	The sequence of tasks with zero float, determining the project's minimum duration

Calculation Steps

1. Topological Sort: Order tasks by dependencies, detecting any circular references
2. Forward Pass: Starting from the initial tasks, compute ES and EF for each task
   • ES = max(EF of all predecessors)
   • EF = ES + Duration
3. Backward Pass: Working back from the final tasks, compute LS and LF
   • LF = min(LS of all successors)
   • LS = LF - Duration
4. Identify the Critical Path: Tasks where float (LS − ES) equals 0 form the critical path

Input Format

A JSON object with the following fields:

{
  "project": "Project Name",
  "start_date": "2026-05-01",
  "tasks": [
    {
      "id": "T1",
      "name": "Task Name",
      "duration": 5,
      "dependencies": ["T0"]
    }
  ]
}

Field	Required	Type	Description
project	No	string	Project title; defaults to "Project Gantt Chart"
start_date	No	string	YYYY-MM-DD format; can be overridden by the CLI --start-date flag
tasks	Yes	array	List of tasks
tasks[].id	Yes	string	Unique task identifier
tasks[].name	Yes	string	Task name
tasks[].duration	Yes	number	Duration in days; must be > 0
tasks[].dependencies	No	array	List of predecessor task IDs; defaults to []

Output Features

The generated HTML file is fully self-contained (no external dependencies) and includes the following interactive features:

• Gantt Chart Visualization: Bar chart with time on the horizontal axis and tasks on the vertical axis
• Critical Path Highlighting: Critical tasks in red, non-critical tasks in blue
• Dependency Arrows: SVG-drawn dependency lines; critical dependencies are bold red
• Float Time Display: Semi-transparent orange areas showing how much a task can be delayed
• Hover Details: Hover over a task to see full CPM analysis data
• Task Highlighting: Click a task to highlight its direct predecessors and successors
• Zoom Control: Slider to adjust timeline granularity
• Critical Path Filter: Toggle to show only critical path tasks
• Today Marker: Green vertical line indicating the current date
• JSON Export: Export the complete dataset with CPM annotations

Script Arguments

python3 scripts/gantt_generator.py [options]

Required (one of):
  --json TEXT          Task data as a JSON string
  --file PATH          Path to a JSON file containing task data

Optional:
  --start-date DATE    Project start date (YYYY-MM-DD); defaults to today
  --output, -o PATH    Output HTML file path; defaults to stdout
  --title TEXT         Override the project title

Full Example

Scenario: Software Development Project Schedule

{
  "project": "CRM System v2.0 Development",
  "start_date": "2026-05-05",
  "tasks": [
    {"id": "A", "name": "Requirements Research", "duration": 5, "dependencies": []},
    {"id": "B", "name": "Architecture Design", "duration": 3, "dependencies": ["A"]},
    {"id": "C", "name": "UI/UX Design", "duration": 4, "dependencies": ["A"]},
    {"id": "D", "name": "Database Design", "duration": 2, "dependencies": ["B"]},
    {"id": "E", "name": "Backend API Development", "duration": 10, "dependencies": ["D"]},
    {"id": "F", "name": "Frontend Development", "duration": 8, "dependencies": ["C", "D"]},
    {"id": "G", "name": "Unit Testing", "duration": 3, "dependencies": ["E"]},
    {"id": "H", "name": "Integration Testing", "duration": 4, "dependencies": ["F", "G"]},
    {"id": "I", "name": "User Acceptance Testing", "duration": 3, "dependencies": ["H"]},
    {"id": "J", "name": "Deployment", "duration": 2, "dependencies": ["I"]}
  ]
}

Analysis results:

• Total duration: 32 days
• Critical path: A → B → D → E → G → H → I → J
• UI/UX Design (C) has float time and can be delayed without affecting the total duration

Notes

• Circular dependencies (A depends on B, B depends on A) are not allowed; the script detects and reports them
• Duration is measured in calendar days; weekdays and holidays are not distinguished
• All task IDs must be unique
• The generated HTML can be opened offline — no internet connection required