# Data Chart

> Use when the user wants a data chart, graph, or plot in the clean editorial blog-figure look: line, bar, scatter, or dot-plot renderings of measured data, produced programmatically with matplotlib and exported to SVG/PNG. Trigger on "chart", "graph", "plot", benchmark-score figures, and requests for minimal blog-style data graphics. NOT for flowcharts, architecture diagrams, or box-and-arrow figures (use technical-diagram), and NOT for interactive dashboards or web-embedded live charts.

- Skill: `gigio1023/data-chart` (Agent Skill, multi-file: 5 files)
- Install (CLI): `npx skillmds@latest add gigio1023/data-chart`
- Raw SKILL.md: https://api.skillmd.com/api/skills/gigio1023/data-chart/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: gigio1023 (https://skillmd.com/u/gigio1023)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/gigio1023/data-chart

---


# Data Chart

Render measured data as static charts in the shared editorial figure language: gridless ink axes, restrained direct labels, and one accent family per page. Titles and legends are optional content, not a fixed page frame. SVG is the primary artifact (text preserved as text); inspect a PNG proof before claiming success.

## Routing: chart or diagram?

Decide by the figure's content, not its name:

- **Measured data** - real numbers, many points, true scales (log axes, distributions, time series) - this skill.
- **Structure** - boxes, arrows, layers, pipelines, or a few illustrative values inside a larger schematic - the sibling `technical-diagram` skill. Use `drawio-diagram` only when native draw.io format is part of the request.
- Borderline (3-8 bars): real measurements that may change → this skill (the chart regenerates from data); a decorative sketch inside a diagram → technical-diagram.

## Quick start

1. Read [`references/chart-language.md`](references/chart-language.md) for the full rule set (anatomy, tokens, marks, dark mode).
2. Write a small script that imports the style module [`scripts/editorial_mpl.py`](scripts/editorial_mpl.py): `ed.use()` → plot with family colors → `ed.mono_ticks` / `ed.axis_label` → optional `ed.header` → `ed.save(fig, stem)` (writes `stem.svg` + `stem.png`). The module reads the vendored canonical values from [`assets/editorial-tokens.json`](assets/editorial-tokens.json). [`scripts/example_chart.py`](scripts/example_chart.py) is a working reference for both a line chart and grouped bars; copy its margin setup (`subplots_adjust` with `top≈0.80` clears the header row).
3. Run it. No system matplotlib is assumed - use `uv run --with matplotlib python <script>.py` (add other deps the same way). `findfont` warnings about Inter/IBM Plex Mono are expected on machines without those fonts; fallbacks carry the voice and the SVG keeps the full stack.
4. **Look at the PNG before finishing.** Check: no clipped direct labels or tick text (widen margins, not the font), any required legend fits on one line, one accent family, and no gridlines or unrequested supporting text.

## Non-negotiables

- Data values come from the user or their files - never invent or "smooth" numbers. Inspect the supplied data before asking. Preserve missing values as gaps when that representation is valid; if omission would change the requested comparison, ask about that series while preparing the supported chart parts. Disclose an omitted series rather than silently dropping it.
- Emphasis comes from color and direct labels, never thicker strokes or bigger fonts.
- Direct value labels on endpoints or one emphasized point only - never every point. Axis and tick text stays ink.
- One y-scale per chart. Two measures of different scale become two charts.
- Deterministic scripts: no RNG, no timestamps in output filenames.
- Do not add a title when the embedding document already names the chart. Do not add a legend when direct labels make every series clear. Never add a subtitle, takeaway strip, source footer, badge, or decorative inset merely to fill the canvas.

## Brand safety

The look is modeled on openai.com editorial figures - geometry, palette, and typographic structure only. Never add the OpenAI logo, blossom mark, or wordmark; never label output as OpenAI-branded or imply affiliation. OpenAI Sans is proprietary - the Inter/IBM Plex Mono stacks in the style module are the approved substitutes.

## Verification before claiming done

1. The script ran cleanly and wrote both `.svg` and `.png`.
2. You rendered and actually viewed the PNG (step 4 above).
3. The SVG contains `<text` elements (fonts preserved), not outlined paths.
4. Every number in the chart traces to user-provided data.

Once these checks pass at the intended display size, deliver the script, SVG, and PNG. Rerender after a data, label, or layout correction; do not create additional chart types or style variants merely to prolong visual review.

## Gotchas

- matplotlib's default `svg.fonttype` is `path`: skipping `ed.use()` (or saving before it runs) silently outlines all text and kills editability. Verification step 3 catches this.
- Endpoint direct labels sit outside the axes and clip at the figure edge; reserve margin first (`subplots_adjust(right≈0.88)`). Fix clipping with margins, never smaller fonts.
- Coral mid (`#FF9365`) fails 3:1 contrast on white - keep coral series dashed or direct-labeled, and set coral value labels in `#804126`.
- `ed.header()` draws the canvas to measure each legend label, so call it after the figure size and margins are final; late `subplots_adjust` calls shift the plot under a already-placed header.
- `findfont` warnings for Inter/IBM Plex Mono are expected on machines without those fonts and are not a failure.