charts

Design

Generate inline chart images (PNG) for embedding in chat responses. Use this skill when you need to create bar, line, or area charts for data visualization in chat.

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Chart Generation

How It Works

Charts are generated server-side as PNG images using chartjs-node-canvas (Chart.js) and served via /api/media/. The generate-chart script renders charts and returns a fully qualified URL for embedding in chat markdown.

Script Usage

pnpm action generate-chart --type=bar --title="Title" --labels='["A","B","C"]' --data='[1,2,3]' --color="#18B4F4"

Parameters

Param	Values	Default
`--type`	`bar`, `line`, `area`	`bar`
`--title`	Chart title (keep SHORT)	required
`--subtitle`	Optional subtitle — avoid unless needed	—
`--labels`	JSON array of x-axis labels	required
`--data`	JSON array of numbers, OR array of `{label, data, color}` for multi-series	required
`--color`	Primary hex color	`#18B4F4`
`--theme`	`dark`, `light`	auto from `/api/theme`
`--stacked`	`true` for stacked bars	`false`
`--filename`	Output filename (no ext)	auto from title
`--width` / `--height`	Image dimensions	800x400

Output

{ filename, url, width, height } — the url is fully qualified with cache buster.

Color Palette

Color	Hex	Use
Blue	`#18B4F4`	Default/primary for all charts
Purple	`#8b5cf6`	Secondary
Green	`#22c55e`	Tertiary
Amber	`#f59e0b`
Indigo	`#6366f1`
Red	`#ef4444`
Teal	`#14b8a6`
Orange	`#f97316`

Style Preferences (from Steve)

Minimal text on chart — short title only, no subtitle
Stats and context in chat text around the chart, not on the image
Large fonts: title 22px, axis 13px
Few axis labels: maxTicksLimit 8 on x-axis, 5 on y-axis
No rotated labels (maxRotation: 0)

Good pattern:

**Example Corp Product Usage — Last 30 Days**
![chart](https://...your-app.example.com/api/media/chart.png?v=123)
**528 messages** over 18 active days | Peak: **89** (Feb 14)

QuickChart Inline Styling (for non-script charts)

When using QuickChart (https://quickchart.io/chart/create) with Chart.js v2:

Background: #09090b (zinc-950)
Grid: horizontal only, dashed [3,3], color #27272a
Axis ticks: #52525b, 11px
Title: #fafafa, 16px bold
Legend: #a1a1aa, 11px
Default bar/line color: #18B4F4 (primary blue)
Tooltips: bg #09090b, border #27272a, text #fafafa

Multi-Series & Stacked Charts

Use --stacked=true flag
Pass data as --data='[{"label":"User A","data":[...],"color":"#..."}]'
Script sets stack: "stack1" on all datasets

Key Gotchas

Relative paths do NOT work — chat UI is on a different origin. Always use the fully qualified URL from script output (uses APP_ORIGIN)
Cache busting (?v=<timestamp>) auto-appended
chartjs-node-canvas depends on canvas native module — pnpm.onlyBuiltDependencies must include "canvas". If not built, run pnpm rebuild canvas
Theme auto-detected from media/theme.json (set by sidebar toggle via POST /api/theme)