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.
npx agentmods add skills/plannotator/effective-html/html-diagramnpx skills add plannotator/effective-html --skill html-diagramgit clone --depth 1 https://github.com/plannotator/effective-htmlWhat 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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00065 | $0.00514 |
| Opus 5 | $0.00032 | $0.00257 |
| Sonnet 5 | $0.00013 | $0.00103 |
| Haiku 4.5 | $0.00006 | $0.00051 |
Grade A, and why
html-diagram 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 yesterday.
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.
How it starts
The opening of the file, as written. The whole thing — 49 lines — stays where its author put it; the contents beside it link to each section on GitHub.
HTML Diagram
Build the smallest visual model that makes the relationship easier to understand than prose alone. Match the notation and visual language to the user's project and subject. Do not force every topic into the same SVG boxes and arrows.
Choose the right model
Identify the question the reader should answer, then select the form:
- topology for components and connections;
- sequence for ordered messages over time;
- process for steps, branches, and handoffs;
- state for transitions and conditions;
- hierarchy for containment or ownership;
- timeline for change over time;
- matrix for repeated relationships;
- quantitative view when magnitude matters.
Decide what must remain visible together and what can be revealed on demand. Use a simpler form when it carries the same meaning.
Choose the rendering method
Use HTML and CSS, SVG, Canvas, or WebGL according to the information and scale. Do not use SVG merely because the output is a diagram.
- Keep labels, grouping, direction, and connectors legible before adding interaction.
- Use stable node positions when readers must compare states or steps.
- Keep edge crossings and ambiguous arrowheads to a minimum.
- Put intentionally broad canvases in a contained pan or scroll region.
- Use legends only when notation is not self-explanatory.
Add sequencing, filtering, path tracing, pan and zoom, or animation only when it helps answer the stated question. Keep overlays dismissible, controls keyboard-accessible, and motion compatible with prefers-reduced-motion.
When design-artifact is available, read it for
the diagram's surrounding composition and visual register. Keep the chosen
diagram grammar, label legibility, and relationships authoritative over
decorative treatment.
Build and verify
Deliver one self-contained HTML file with essential CSS and JavaScript inline. Require no build step or external service. Use accessible text alternatives and keep important meaning available without animation or color alone.
What ships with it
1 file 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.
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.
- yesterday First seen · 49 lines · 65 tokens per session scan A a3641a37be2f
html-diagram is a skill published in the GitHub repository plannotator/effective-html (2,735 stars, last pushed 28d ago), licensed MIT. It adds 65 tokens to every session and 514 once invoked, about $0.0003 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 2026-08-30.
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