CLI reference — chartjs2img llm ​

This is a reference page, not a tutorial. Start with one of the tutorials (Claude plugin / gh skill / context7) if you haven't installed anything yet.

One chartjs2img subcommand exists specifically for LLM consumption: chartjs2img llm. It prints a self-contained Markdown reference of Chart.js core plus every bundled plugin. Pipe it into your agent's context on session start and configs come out right first try.

Usage ​

chartjs2img llm

• No network access.
• No arguments.
• Stdout only.

The output covers:

• Usage guide — how to invoke chartjs2img (CLI vs HTTP), input JSON shape, constraints (JSON only, no functions), and caveats.
• Chart.js core — all 8 built-in chart types (bar, line, pie, doughnut, radar, polarArea, scatter, bubble), dataset properties, scales, and the title / legend / tooltip plugin option trees.
• Bundled plugin options — 12 sections:
  • chartjs-plugin-datalabels
  • chartjs-plugin-annotation
  • chartjs-plugin-zoom
  • chartjs-plugin-gradient
  • chartjs-chart-treemap
  • chartjs-chart-matrix
  • chartjs-chart-sankey
  • chartjs-chart-wordcloud
  • chartjs-chart-geo
  • chartjs-chart-graph
  • chartjs-chart-venn
  • chartjs-adapter-dayjs-4

Each section includes option tables (property path, type, default, description) and a JSON example.

The Markdown is regenerated from source (src/llm-docs/*.ts) on every build, so it can never drift from the implementation.

Output shape at a glance ​

Approximate structure:

# Usage

<input JSON shape, HTTP vs CLI, JSON constraint, error feedback, exit codes>

## Chart.js core (chart.js@4.4.9)

<type, data, datasets, options, scales, title, legend, tooltip>

## Datalabels (chartjs-plugin-datalabels)

<display, anchor, align, color, font — including the chartjs2img-specific
 "off by default" policy>

## Annotation (chartjs-plugin-annotation)

<line, box, label, point, polygon, ellipse>

## Zoom (chartjs-plugin-zoom)

...

## Gradient (chartjs-plugin-gradient)

...

<plus the 7 additional chart-type plugins and the date adapter>

Total output: ~1400 lines, ~135 KB. Fits comfortably in modern context windows.

Agent prompt templates ​

Minimal — opening turn ​

You are going to author Chart.js configurations that chartjs2img will
render to images. The complete reference follows. When you produce a
JSON config:
1. Validate with `chartjs2img render -i <file> -o /tmp/check.png 2> /tmp/check.err`.
2. If /tmp/check.err is non-empty, fix and retry.
3. Report the final JSON plus the rendered image path.

---
<paste output of `chartjs2img llm`>
---

Richer — with explicit gotchas ​

<above>

Gotchas to remember:
- JSON has no functions — do not use `options.scales.y.ticks.callback` or `datalabels.formatter`.
- Animation is forced OFF internally — don't propose animated configs.
- Datalabels is disabled by default — set `options.plugins.datalabels.display: true` to show labels.
- Time-series axes need `"type": "time"` — the dayjs adapter is bundled.

Piping into standard LLM CLIs ​

OpenAI / generic llm CLI ​

chartjs2img llm \
  | llm -s "Generate a Chart.js config for monthly sales, Jan-Jun, values 12 19 3 5 2 15"

Clipboard (macOS) ​

chartjs2img llm | pbcopy

Then paste into your agent's system-prompt box.

File ​

chartjs2img llm > /tmp/chartjs2img-reference.md

Re-use across sessions.

Relationship to other AI channels ​

• llms-full.txt on the docs site has a superset — it appends every docs/en/ Markdown page to the same reference. Use it if your agent wants both the reference and the guide pages in one payload.
• context7 retrieves the same content via MCP when a full-bundle is too big for your context window.
• chartjs2img-author SKILL.md inlines the JSON shape, the error feedback contract, and a plugin catalog so the skill is self-contained. Agents fall back to chartjs2img llm only when they need the full option tables for a specific plugin.

Whichever channel an agent uses, the actual content is derived from the same src/llm-docs/*.ts files, so consistency is guaranteed.

Extending ​

To add / change what chartjs2img llm outputs, edit the relevant file under src/llm-docs/. See the Developer Guide → Adding LLM docs for the full format.

Troubleshooting ​

chartjs2img: command not found — install the binary first. See Install or run /chartjs2img-install if you have the Claude plugin.

Output is empty — that would be a bug; file an issue. The aggregator always has at least the usage section.

Output looks outdated — check chartjs2img --version. Each release rebuilds src/llm-docs/ from the pinned plugin versions in src/template.ts; old binaries reflect old plugin versions.

See also ​

• AI Guide overview — pick a tutorial.
• llms.txt — the same reference served as a static file.
• Developer Guide → Adding LLM docs — how to extend the output.