chart-design

A guide to designing honest, accessible charts for numerical data as inline SVG images. It covers common charts such as bars, lines, distributions, scatter plots, and small multiples.

In plain words
What is it for?
Use it to choose chart types, label data, select colors, and build charts for measured values, trends, distributions, and comparisons.
Why use it?
It helps charts communicate comparisons accurately and avoids misleading choices such as truncated bar axes or unnamed percentage denominators.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/avinava/document-design-system/chart-design
Any agent
npx skills add Avinava/document-design-system --skill chart-design
Clone the repo
git clone --depth 1 https://github.com/Avinava/document-design-system

Made for: Claude Code, Codex.

Per session 131 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,848 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00131 $0.01848
Opus 5 $0.00066 $0.00924
Sonnet 5 $0.00026 $0.00370
Haiku 4.5 $0.00013 $0.00185

Measured 2d ago against content hash a547aa940a56, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

chart-design scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/chart-design/SKILL.md · 131 lines

How it starts

The opening of the file, as written. The whole thing — 131 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Chart Design

A chart is an argument about numbers. Its job is to make one comparison faster than a table would — and to make the wrong reading hard.

Choose a chart only when it reveals a relationship faster than a table. A chart of four values is slower to read than four labelled numbers, because the reader has to decode the encoding before they get the data.

The honesty rules

These are not stylistic. Breaking them changes what the reader concludes.

  • Bar and column charts start at zero. A truncated bar axis multiplies apparent differences by an arbitrary factor. If small differences matter, use a line chart, a dot plot, or state the values.
  • Line charts may use a non-zero axis — they encode position, not length — but the axis must be labelled and the truncation visible.
  • Area encodes one quantity, not two. Doubling both width and height quadruples the area for a doubled value.
  • Percentages name their denominator, near the chart, not buried in a footnote.
  • Equal visual weight means equal comparability. Do not put two different units on one axis.
  • Time on an axis is continuous. Missing months appear as zero or as a marked gap, never by silently closing up.
  • State when a scale is logarithmic, in the axis label, not the caption.
  • Categories are categories, even when they look like numbers. Years, quarters, ports, and version numbers are labels, not measurements. Put them on a categorical (band) scale. Left on a continuous scale, 2020…2025 gets positioned by arithmetic distance, and a missing year silently becomes a gap the data never had.

If the data does not support the chart's implicit claim, change the chart, not the axis.

Choosing a form

The reader needs Form
Rank and compare categories Horizontal bars, sorted descending
Compare a value across time periods Columns, chronological
A trend, or many series over time Line
Used versus available against a limit Limit ledger (single track)
Composition of a whole, 2–3 parts Stacked bar, labelled
Composition of a whole, many parts Ranked bars — not a pie
Relationship between two measures Scatter
The same comparison across groups Small multiples
Distribution shape Histogram or box plot

Read the full file on GitHub · 131 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 131 lines · 131 tokens per session scan A a547aa940a56

Subscribe to this mod's changes

chart-design is a skill published in the GitHub repository Avinava/document-design-system (2 stars, last pushed 7d ago), licensed MIT. It adds 131 tokens to every session and 1,848 once invoked, about $0.0007 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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