jsonantt 2026.10

Generate Gantt charts from JSON descriptions using matplotlib

jsonantt

jsonantt generates beautiful Gantt chart images from a simple JSON description.
Charts are rendered with matplotlib so they can be saved as .png, .pdf, .svg, and more.

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Features

• Infinitely nestable tasks — define sub-tasks, sub-sub-tasks, etc.
• Auto date computation — parent task start/end are derived automatically from children when not specified.
• Milestone markers — easy "milestone": true flag with chart-level defaults and per-milestone marker overrides.
• Optional task descriptions and extra fields — add long-form context per task, plus arbitrary metadata like assignee or cost for table output.
• Fully colourable — set colours per-task; children inherit their parent's colour.
• Recursive child colour lightening — inherited subtask colours can optionally lighten at each nested level.
• Clean, indented y-axis labels — task names are left-aligned with proper indentation per depth level.
• Table output mode — render a task summary table with the same hierarchy and colour cues.
• PNG / PDF / SVG output — whatever matplotlib supports.

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Installation

pip install jsonantt

Or, directly from source:

git clone https://github.com/briday1/jsonantt.git
cd jsonantt
pip install -e .

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Quick start

1. Create a JSON description

{
  "title": "My Project",
  "dateformat": "%Y-%m-%d",
  "style": {
    "milestone_color": "#FFD700",
    "milestone_marker": "D"
  },
  "tasks": [
    {
      "name": "Phase 1 – Planning",
      "children": [
        { "name": "Requirements", "start": "2024-01-08", "end": "2024-01-19" },
        { "name": "Architecture",  "start": "2024-01-15", "end": "2024-01-31" }
      ]
    },
    { "name": "Planning done", "milestone": true, "date": "2024-01-31" },
    {
      "name": "Phase 2 – Build",
      "color": "#70AD47",
      "children": [
        { "name": "Backend",  "start": "2024-02-01", "end": "2024-03-01" },
        { "name": "Frontend", "start": "2024-02-12", "end": "2024-03-08" }
      ]
    },
    { "name": "Launch", "milestone": true, "date": "2024-04-01", "color": "#FF5757" }
  ]
}

2. Generate the chart or table

CLI:

jsonantt project.json project.png
jsonantt project.json project.pdf   # vector PDF
jsonantt project.json project.svg   # scalable SVG
jsonantt --dpi 300 project.json project.png   # high-resolution PNG
jsonantt -r 1 project.json project.png   # top-level tasks only
jsonantt --renderdepth 2 project.json project.png   # include one child level
jsonantt -t project.json project-table.png   # task name / description table
jsonantt -t project.json project-table.csv   # CSV table export
jsonantt agreed.json compare.png --compare actual.json   # outline vs actual compare chart
jsonantt -t agreed.json compare-table.csv --compare actual.json   # compare table with signed offsets
jsonantt project.json project.png --date-line today --date-line-color "#C00000"   # single target line

Python API:

from jsonantt import load_chart, render_chart, render_compare_chart, render_compare_table, render_table

config = load_chart("project.json")
actual = load_chart("actual.json")
render_chart(config, "project.png", dpi=150)
render_chart(config, "summary.png", dpi=150, render_depth=1)
render_table(config, "project-table.png", dpi=150)
render_compare_chart(config, actual, "compare.png", dpi=150)
render_compare_table(config, actual, "compare-table.csv", dpi=150)

render_depth=0 renders all nested levels. 1 renders only top-level tasks, 2 includes one level of children, and so on.

--table / -t switches the output to a table view. By default it renders Task, Name, and Description. The Task column keeps hierarchy numbering, the Name column stays unindented, style.table_colorize controls the side color accent, and style.table_show_markers controls whether milestone rows use a diamond marker in that gutter.

You can customize the table columns with style.table_columns. Each entry can be either a string field name or an object with field and optional title. The special fields task, name, and description preserve the existing behavior; any other field is read from the task object, including extra task keys like assignee or cost.

{
  "style": {
    "table_columns": [
      "task",
      "name",
      { "field": "assignee", "title": "Owner" },
      { "field": "cost", "title": "Cost" },
      "description"
    ]
  },
  "tasks": [
    {
      "name": "API Design",
      "start": "2024-01-01",
      "end": "2024-01-10",
      "assignee": "Morgan",
      "cost": 1200,
      "description": "Finalize endpoints and review contracts."
    }
  ]
}

Description and Name cells wrap to the measured rendered width of the column, and the row height expands to fit the wrapped lines. Very long unbroken tokens are not split mid-word, so they can still clip horizontally.

--milestones-only works with --table to render only milestone rows in a dedicated milestone table. --no-milestones does the opposite and excludes milestones.

If the table output path ends in .csv, jsonantt writes CSV instead of an image.

--compare turns the first JSON input into the planned/agreed baseline and overlays the second JSON as the updated/actual state. In compare charts, planned bars are drawn as slightly larger unfilled outlines, actual bars are drawn normally, removed planned tasks are struck through with no actual bar, and actual-only tasks render as normal filled bars. In compare tables and CSV output, the Offset column shows signed duration changes like +2d, -1w, +3mo, or +1y; milestones use the signed date shift instead.

Use --date-line to draw a single vertical reference line on chart outputs. It accepts either a date in the input file's dateformat or the special value today. Use --date-line-color to control its color.

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JSON reference

Field	Type	Description
title	string	Optional chart title shown at the top
dateformat	string	strptime format string (default: "%Y-%m-%d")
start	date string	Optional chart x-axis start date (overrides task dates)
end	date string	Optional chart x-axis end date
style	object	Visual style overrides (see below)
tasks	array	Top-level list of task objects

Task object

Field	Type	Description
name	string	Required. Task label
description	string	Optional long-form text used by table output
any other key	any JSON value	Preserved on the task and available to style.table_columns for table output
id	string	Unique identifier used for not_before references
start	date string	Bar start date
end	date string	Bar end date
duration	string or int	Duration from start (or resolved not_before end): "14d", "2w", "3m", "2y", or a plain integer (days)
not_before	string	id of another task — this task starts immediately after that task ends
color	CSS hex string	Bar colour, or milestone colour override for an individual milestone (e.g. "#4472C4")
milestone	boolean	Render as a diamond milestone instead of a bar
date	date string	Milestone date (used when milestone: true)
marker	string	Milestone marker override for an individual milestone (matplotlib marker symbol such as "D", "o", "s", "*")
marker_size	number	Override milestone diamond size in points
bold	boolean	Render label in bold (top-level tasks are auto-bolded by default)
children	array	Nested sub-tasks (infinitely nestable)

Auto date computation: When a task has children but no explicit start/end, the dates are computed automatically as the earliest child start and latest child end, recursively.

Duration formats: d/day/days, w/week/weeks, m/month/months, y/year/years — e.g. "14d", "2w", "3m", "1y".

Style object

Field	Default	Description
width	14	Figure width in inches
row_height	0.3	Height of each task row in inches
bar_height	0.5	Bar height as a fraction of row_height
font_size	12	Base font size in points
indent_size	3	Spaces added per depth level in labels
label_fraction	0.0	Fraction of figure width used for labels; 0 means auto-size from measured text width
subtask_lightening_pct	0.0	Percentage to lighten inherited subtask colours at each nested level; 20 means each inherited step moves 20% toward white
colors	palette	Array of default hex colours cycled per top-level task
background	"#FFFFFF"	Figure background colour
grid_color	"#E0E0E0"	Vertical gridline colour
row_band_color	"#F5F5F5"	Alternating row band colour
milestone_color	"#FFD700"	Default milestone colour
milestone_marker	"D"	Default milestone marker symbol
milestone_size	14	Default milestone marker size in points
major_tick	null	Major tick unit: "year", "quarter", "month", "week"
minor_tick	null	Minor tick unit: "quarter", "month", "week", "day"
major_grid_width	2.0	Major gridline linewidth
minor_grid_width	1.5	Minor gridline linewidth
tick_position	"top"	X-axis label position: "top", "bottom", or "both"
bold_tasks	true	Auto-bold top-level (depth 0) task labels
number_tasks	true	Prefix task labels with hierarchy numbers like 1, 1.1, 1.2
table_colorize	true	Show a task-coloured accent bar in table output; when false, both accent bars and milestone markers are suppressed
table_show_markers	true	Replace the accent bar with a milestone diamond for milestone rows in table output when table colours are enabled
table_columns	[]	Ordered table column definitions. Empty means the default Task, Name, Description columns. Entries can be field-name strings or objects like { "field": "cost", "title": "Cost" }

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Examples

See the examples/ folder for ready-to-run JSON files.

Simple project

examples/simple.json — a five-phase project with milestones

Dependencies

examples/dependencies.json — id, duration, and not_before

Render depth

examples/renderdepth.json — nested tasks that are useful with -r / --renderdepth

Full depth, render_depth=0:

One child level, -r 2:

Top level only, -r 1:

Table output, -t:

Milestones only, -t --milestones-only:

No milestones, -t --no-milestones:

Try the same file with different depth limits:

jsonantt examples/renderdepth.json examples/renderdepth-all.png      # full depth
jsonantt -r 1 examples/renderdepth.json examples/renderdepth-top.png # top-level only
jsonantt -r 2 examples/renderdepth.json examples/renderdepth-mid.png # one child level
jsonantt -t examples/renderdepth.json examples/renderdepth-table.png # task table view
jsonantt -t --milestones-only examples/renderdepth.json examples/renderdepth-milestones.png # milestones only
jsonantt -t --no-milestones examples/renderdepth.json examples/renderdepth-no-milestones.png # exclude milestones
jsonantt -t examples/renderdepth.json examples/renderdepth-table.csv # CSV table export

Color schemes

examples/colors.json — custom palette, background, grid, row band, milestone colours, and custom milestone markers

Compare mode

examples/compare-planned.json and examples/compare-actual.json — planned vs actual comparison with a CLI date line

Compare chart:

Compare table image:

CSV export:

examples/compare-table.csv

Description wrapping

examples/description-wrap.json — demonstrates normal word wrapping in table output and the edge case where a single unbroken token will not wrap

Table output, -t:

CSV export:

examples/description-wrap-table.csv

Custom table fields

examples/costs.json — shows style.table_columns with custom Owner and Cost columns sourced from task fields like assignee and cost

CSV export:

examples/costs-table.csv

Complex roadmap

examples/complex.json — a multi-year roadmap with deep nesting, task descriptions, and custom colours

Table output, -t:

Milestones only, -t --milestones-only:

No milestones, -t --no-milestones:

How to Run

jsonantt examples/simple.json examples/simple.png                    # basic milestones
jsonantt examples/dependencies.json examples/dependencies.png        # not_before scheduling
jsonantt examples/renderdepth.json examples/renderdepth.png          # full nested view
jsonantt -r 1 examples/renderdepth.json examples/renderdepth-top.png # top-level only
jsonantt -r 2 examples/renderdepth.json examples/renderdepth-mid.png # one child level
jsonantt -t examples/renderdepth.json examples/renderdepth-table.png # task table with descriptions
jsonantt -t --milestones-only examples/renderdepth.json examples/renderdepth-milestones.png # milestone table
jsonantt -t --no-milestones examples/renderdepth.json examples/renderdepth-no-milestones.png # table without milestones
jsonantt -t examples/renderdepth.json examples/renderdepth-table.csv # CSV export
jsonantt examples/colors.json examples/colors.png                    # custom palette and background
jsonantt examples/compare-planned.json examples/compare.png --compare examples/compare-actual.json --date-line 2024-03-01 --date-line-color "#C00000" # compare chart with target line
jsonantt -t examples/compare-planned.json examples/compare-table.png --compare examples/compare-actual.json # compare table image
jsonantt -t examples/compare-planned.json examples/compare-table.csv --compare examples/compare-actual.json # compare table CSV
jsonantt -t examples/description-wrap.json examples/description-wrap-table.png # wrapped descriptions table image
jsonantt -t examples/description-wrap.json examples/description-wrap-table.csv # wrapped descriptions CSV
jsonantt -t examples/costs.json examples/costs-table.csv                # custom cost/owner columns CSV
jsonantt examples/complex.json examples/complex.png                  # deep roadmap example
jsonantt -t examples/complex.json examples/complex-table.png         # full complex table
jsonantt -t --milestones-only examples/complex.json examples/complex-milestones.png # complex milestones only
jsonantt -t --no-milestones examples/complex.json examples/complex-no-milestones.png # complex without milestones