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

Topological Sort: Order tasks by dependencies, detecting any circular references
Forward Pass: Starting from the initial tasks, compute ES and EF for each task
- ES = max(EF of all predecessors)
- EF = ES + Duration
Backward Pass: Working back from the final tasks, compute LS and LF
- LF = min(LS of all successors)
- LS = LF - Duration
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

gantt-planner

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

Quick Start