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Chart Image

Generate publication-quality chart images from data.

Rating
4.3 (161 reviews)
Downloads
2,038 downloads
Version
1.0.0

Overview

Generate publication-quality chart images from data.

Complete Documentation

View Source →

Chart Image Generator

Generate PNG chart images from data using Vega-Lite. Perfect for headless server environments.

Why This Skill?

Built for Fly.io / VPS / Docker deployments:

  • ✅ No native compilation - Uses Sharp with prebuilt binaries (unlike canvas which requires build tools)
  • ✅ No Puppeteer/browser - Pure Node.js, no Chrome download, no headless browser overhead
  • ✅ Lightweight - ~15MB total dependencies vs 400MB+ for Puppeteer-based solutions
  • ✅ Fast cold starts - No browser spinup delay, generates charts in <500ms
  • ✅ Works offline - No external API calls (unlike QuickChart.io)

Setup (one-time)

bash
cd /data/clawd/skills/chart-image/scripts && npm install

Quick Usage

bash
node /data/clawd/skills/chart-image/scripts/chart.mjs \
  --type line \
  --data '[{"x":"10:00","y":25},{"x":"10:30","y":27},{"x":"11:00","y":31}]' \
  --title "Price Over Time" \
  --output chart.png

Chart Types

Line Chart (default)

bash
node chart.mjs --type line --data '[{"x":"A","y":10},{"x":"B","y":15}]' --output line.png

Bar Chart

bash
node chart.mjs --type bar --data '[{"x":"A","y":10},{"x":"B","y":15}]' --output bar.png

Area Chart

bash
node chart.mjs --type area --data '[{"x":"A","y":10},{"x":"B","y":15}]' --output area.png

Pie / Donut Chart

bash
# Pie
node chart.mjs --type pie --data '[{"category":"A","value":30},{"category":"B","value":70}]' \
  --category-field category --y-field value --output pie.png

# Donut (with hole)
node chart.mjs --type donut --data '[{"category":"A","value":30},{"category":"B","value":70}]' \
  --category-field category --y-field value --output donut.png

Candlestick Chart (OHLC)

bash
node chart.mjs --type candlestick \
  --data '[{"x":"Mon","open":100,"high":110,"low":95,"close":105}]' \
  --open-field open --high-field high --low-field low --close-field close \
  --title "Stock Price" --output candle.png

Heatmap

bash
node chart.mjs --type heatmap \
  --data '[{"x":"Mon","y":"Week1","value":5},{"x":"Tue","y":"Week1","value":8}]' \
  --color-value-field value --color-scheme viridis \
  --title "Activity Heatmap" --output heatmap.png

Multi-Series Line Chart

Compare multiple trends on one chart:
bash
node chart.mjs --type line --series-field "market" \
  --data '[{"x":"Jan","y":10,"market":"A"},{"x":"Jan","y":15,"market":"B"}]' \
  --title "Comparison" --output multi.png

Stacked Bar Chart

bash
node chart.mjs --type bar --stacked --color-field "category" \
  --data '[{"x":"Mon","y":10,"category":"Work"},{"x":"Mon","y":5,"category":"Personal"}]' \
  --title "Hours by Category" --output stacked.png

Volume Overlay (Dual Y-axis)

Price line with volume bars:
bash
node chart.mjs --type line --volume-field volume \
  --data '[{"x":"10:00","y":100,"volume":5000},{"x":"11:00","y":105,"volume":3000}]' \
  --title "Price + Volume" --output volume.png

Sparkline (mini inline chart)

bash
node chart.mjs --sparkline --data '[{"x":"1","y":10},{"x":"2","y":15}]' --output spark.png
Sparklines are 80x20 by default, transparent, no axes.

Options Reference

Basic Options

OptionDescriptionDefault
--typeChart type: line, bar, area, point, pie, donut, candlestick, heatmapline
--dataJSON array of data points-
--outputOutput file pathchart.png
--titleChart title-
--widthWidth in pixels600
--heightHeight in pixels300

Axis Options

OptionDescriptionDefault
--x-fieldField name for X axisx
--y-fieldField name for Y axisy
--x-titleX axis labelfield name
--y-titleY axis labelfield name
--x-typeX axis type: ordinal, temporal, quantitativeordinal
--y-domainY scale as "min,max"auto

Visual Options

OptionDescriptionDefault
--colorLine/bar color#e63946
--darkDark mode themefalse
--svgOutput SVG instead of PNGfalse
--color-schemeVega color scheme (category10, viridis, etc.)-

Alert/Monitor Options

OptionDescriptionDefault
--show-changeShow +/-% change annotation at last pointfalse
--focus-changeZoom Y-axis to 2x data rangefalse
--focus-recent NShow only last N data pointsall
--show-valuesLabel min/max peak pointsfalse

Multi-Series/Stacked Options

OptionDescriptionDefault
--series-fieldField for multi-series line charts-
--stackedEnable stacked bar modefalse
--color-fieldField for stack/color categories-

Candlestick Options

OptionDescriptionDefault
--open-fieldOHLC open fieldopen
--high-fieldOHLC high fieldhigh
--low-fieldOHLC low fieldlow
--close-fieldOHLC close fieldclose

Pie/Donut Options

OptionDescriptionDefault
--category-fieldField for pie slice categoriesx
--donutRender as donut (with center hole)false

Heatmap Options

OptionDescriptionDefault
--color-value-fieldField for heatmap intensityvalue
--y-category-fieldY axis category fieldy

Dual-Axis Options (General)

OptionDescriptionDefault
--y2-fieldSecond Y axis field (independent right axis)-
--y2-titleTitle for second Y axisfield name
--y2-colorColor for second series#60a5fa (dark) / #2563eb (light)
--y2-typeChart type for second axis: line, bar, arealine
Example: Revenue bars (left) + Churn area (right):
bash
node chart.mjs \
  --data '[{"month":"Jan","revenue":12000,"churn":4.2},...]' \
  --x-field month --y-field revenue --type bar \
  --y2-field churn --y2-type area --y2-color "#60a5fa" \
  --y-title "Revenue ($)" --y2-title "Churn (%)" \
  --x-sort none --dark --title "Revenue vs Churn"

Volume Overlay Options (Candlestick)

OptionDescriptionDefault
--volume-fieldField for volume bars (enables dual-axis)-
--volume-colorColor for volume bars#4a5568

Formatting Options

OptionDescriptionDefault
--y-formatY axis format: percent, dollar, compact, decimal4, integer, scientific, or d3-format stringauto
--subtitleSubtitle text below chart title-
--hlineHorizontal reference line: "value" or "value,color" or "value,color,label" (repeatable)-

Annotation Options

OptionDescriptionDefault
--annotationStatic text annotation-
--annotationsJSON array of event markers-

Alert-Style Chart (recommended for monitors)

bash
node chart.mjs --type line --data '[...]' \
  --title "Iran Strike Odds (48h)" \
  --show-change --focus-change --show-values --dark \
  --output alert.png

For recent action only:

bash
node chart.mjs --type line --data '[hourly data...]' \
  --focus-recent 4 --show-change --focus-change --dark \
  --output recent.png

Timeline Annotations

Mark events on the chart:

bash
node chart.mjs --type line --data '[...]' \
  --annotations '[{"x":"14:00","label":"News broke"},{"x":"16:30","label":"Press conf"}]' \
  --output annotated.png

Temporal X-Axis

For proper time series with date gaps:

bash
node chart.mjs --type line --x-type temporal \
  --data '[{"x":"2026-01-01","y":10},{"x":"2026-01-15","y":20}]' \
  --output temporal.png

Use --x-type temporal when X values are ISO dates and you want spacing to reflect actual time gaps (not evenly spaced).

Y-Axis Formatting

Format axis values for readability:

bash
# Dollar amounts
node chart.mjs --data '[...]' --y-format dollar --output revenue.png
# → $1,234.56

# Percentages (values as decimals 0-1)
node chart.mjs --data '[...]' --y-format percent --output rates.png
# → 45.2%

# Compact large numbers
node chart.mjs --data '[...]' --y-format compact --output users.png
# → 1.2K, 3.4M

# Crypto prices (4 decimal places)
node chart.mjs --data '[...]' --y-format decimal4 --output molt.png
# → 0.0004

# Custom d3-format string
node chart.mjs --data '[...]' --y-format ',.3f' --output custom.png

Available shortcuts: percent, dollar/usd, compact, integer, decimal2, decimal4, scientific

Chart Subtitle

Add context below the title:

bash
node chart.mjs --title "MOLT Price" --subtitle "20,668 MOLT held" --data '[...]' --output molt.png

Theme Selection

Use --dark for dark mode. Auto-select based on time:

  • Night (20:00-07:00 local): --dark
  • Day (07:00-20:00 local): light mode (default)

Piping Data

bash
echo '[{"x":"A","y":1},{"x":"B","y":2}]' | node chart.mjs --output out.png

Custom Vega-Lite Spec

For advanced charts:

bash
node chart.mjs --spec my-spec.json --output custom.png

⚠️ IMPORTANT: Always Send the Image!

After generating a chart, always send it back to the user's channel. Don't just save to a file and describe it — the whole point is the visual.

bash
# 1. Generate the chart
node chart.mjs --type line --data '...' --output /data/clawd/tmp/my-chart.png

# 2. Send it! Use message tool with filePath:
#    action=send, target=<channel_id>, filePath=/data/clawd/tmp/my-chart.png

Tips:

  • Save to /data/clawd/tmp/ (persistent) not /tmp/ (may get cleaned)
  • Use action=send with filePath — thread-reply does NOT support file attachments
  • Include a brief caption in the message text
  • Auto-use --dark between 20:00-07:00 Israel time
Updated: 2026-02-04 - Added --y-format (percent/dollar/compact/decimal4) and --subtitle

Installation

Terminal bash 

openclaw install chart-image
Copied!

💻Code Examples

--output chart.png

---output-chartpng.txt
## Chart Types

### Line Chart (default)

--title "Activity Heatmap" --output heatmap.png

---title-activity-heatmap---output-heatmappng.txt
### Multi-Series Line Chart
Compare multiple trends on one chart:

--title "Hours by Category" --output stacked.png

---title-hours-by-category---output-stackedpng.txt
### Volume Overlay (Dual Y-axis)
Price line with volume bars:

node chart.mjs --sparkline --data '[{"x":"1","y":10},{"x":"2","y":15}]' --output spark.png

node-chartmjs---sparkline---data-x1y10x2y15---output-sparkpng.txt
Sparklines are 80x20 by default, transparent, no axes.

## Options Reference

### Basic Options
| Option | Description | Default |
|--------|-------------|---------|
| `--type` | Chart type: line, bar, area, point, pie, donut, candlestick, heatmap | line |
| `--data` | JSON array of data points | - |
| `--output` | Output file path | chart.png |
| `--title` | Chart title | - |
| `--width` | Width in pixels | 600 |
| `--height` | Height in pixels | 300 |

### Axis Options
| Option | Description | Default |
|--------|-------------|---------|
| `--x-field` | Field name for X axis | x |
| `--y-field` | Field name for Y axis | y |
| `--x-title` | X axis label | field name |
| `--y-title` | Y axis label | field name |
| `--x-type` | X axis type: ordinal, temporal, quantitative | ordinal |
| `--y-domain` | Y scale as "min,max" | auto |

### Visual Options
| Option | Description | Default |
|--------|-------------|---------|
| `--color` | Line/bar color | #e63946 |
| `--dark` | Dark mode theme | false |
| `--svg` | Output SVG instead of PNG | false |
| `--color-scheme` | Vega color scheme (category10, viridis, etc.) | - |

### Alert/Monitor Options
| Option | Description | Default |
|--------|-------------|---------|
| `--show-change` | Show +/-% change annotation at last point | false |
| `--focus-change` | Zoom Y-axis to 2x data range | false |
| `--focus-recent N` | Show only last N data points | all |
| `--show-values` | Label min/max peak points | false |

### Multi-Series/Stacked Options
| Option | Description | Default |
|--------|-------------|---------|
| `--series-field` | Field for multi-series line charts | - |
| `--stacked` | Enable stacked bar mode | false |
| `--color-field` | Field for stack/color categories | - |

### Candlestick Options
| Option | Description | Default |
|--------|-------------|---------|
| `--open-field` | OHLC open field | open |
| `--high-field` | OHLC high field | high |
| `--low-field` | OHLC low field | low |
| `--close-field` | OHLC close field | close |

### Pie/Donut Options
| Option | Description | Default |
|--------|-------------|---------|
| `--category-field` | Field for pie slice categories | x |
| `--donut` | Render as donut (with center hole) | false |

### Heatmap Options
| Option | Description | Default |
|--------|-------------|---------|
| `--color-value-field` | Field for heatmap intensity | value |
| `--y-category-field` | Y axis category field | y |

### Dual-Axis Options (General)
| Option | Description | Default |
|--------|-------------|---------|
| `--y2-field` | Second Y axis field (independent right axis) | - |
| `--y2-title` | Title for second Y axis | field name |
| `--y2-color` | Color for second series | #60a5fa (dark) / #2563eb (light) |
| `--y2-type` | Chart type for second axis: line, bar, area | line |

**Example:** Revenue bars (left) + Churn area (right):

--x-sort none --dark --title "Revenue vs Churn"

---x-sort-none---dark---title-revenue-vs-churn.txt
### Volume Overlay Options (Candlestick)
| Option | Description | Default |
|--------|-------------|---------|
| `--volume-field` | Field for volume bars (enables dual-axis) | - |
| `--volume-color` | Color for volume bars | #4a5568 |

### Formatting Options
| Option | Description | Default |
|--------|-------------|---------|
| `--y-format` | Y axis format: percent, dollar, compact, decimal4, integer, scientific, or d3-format string | auto |
| `--subtitle` | Subtitle text below chart title | - |
| `--hline` | Horizontal reference line: "value" or "value,color" or "value,color,label" (repeatable) | - |

### Annotation Options
| Option | Description | Default |
|--------|-------------|---------|
| `--annotation` | Static text annotation | - |
| `--annotations` | JSON array of event markers | - |

## Alert-Style Chart (recommended for monitors)

--output recent.png

---output-recentpng.txt
## Timeline Annotations

Mark events on the chart:

--output annotated.png

---output-annotatedpng.txt
## Temporal X-Axis

For proper time series with date gaps:

--output temporal.png

---output-temporalpng.txt
Use `--x-type temporal` when X values are ISO dates and you want spacing to reflect actual time gaps (not evenly spaced).

## Y-Axis Formatting

Format axis values for readability:

node chart.mjs --data '[...]' --y-format ',.3f' --output custom.png

node-chartmjs---data----y-format-3f---output-custompng.txt
Available shortcuts: `percent`, `dollar`/`usd`, `compact`, `integer`, `decimal2`, `decimal4`, `scientific`

## Chart Subtitle

Add context below the title:

node chart.mjs --title "MOLT Price" --subtitle "20,668 MOLT held" --data '[...]' --output molt.png

node-chartmjs---title-molt-price---subtitle-20668-molt-held---data----output-moltpng.txt
## Theme Selection

Use `--dark` for dark mode. Auto-select based on time:
- **Night (20:00-07:00 local)**: `--dark`
- **Day (07:00-20:00 local)**: light mode (default)

## Piping Data

Tags

#image_and-video-generation #data

Quick Info

Category Content Creation
Model Claude 3.5
Complexity One-Click
Author dannyshmueli
Last Updated 3/10/2026
🚀
Optimized for
Claude 3.5
🧠

Ready to Install?

Get started with this skill in seconds

openclaw install chart-image

Resources

📂
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