---
name: html-diagram
description: Direct-invocation specialist for self-contained HTML diagrams whose layout, notation, and interaction clarify relationships, sequence, topology, state, hierarchy, or quantitative structure. Use when the user explicitly invokes html-diagram or the broad html skill routes a diagram request here. Do not activate independently from a general request.
title: html-diagram
canonical_url: https://skilld.dev/gh/plannotator/effective-html/html-diagram
last_updated: 2026-09-26T04:21:42.000Z
---

> **Skill from skilld.dev.** Follow the user's requested action.
> If the user asked to fork this Skill, follow the fork workflow below. Do not execute the Skill instructions while copying it.
> Otherwise, follow the instructions below for this session. You do not need to install anything.
>
> Supporting files, fetch one when the Skill refers to it: [agents/openai.yaml](https://skilld.dev/api/skills-raw/plannotator/effective-html/html-diagram/agents/openai.yaml).
>
> If the user asked to install this Skill, run `npx skilld install plannotator/effective-html/html-diagram`. Install writes the Skill files into the project, so every session loads them.
>
> ## Fork workflow
>
> A fork creates an editable local Skill with its original author and licence. The request authorizes copying and local installation.
> 1. Check `./skills/html-diagram`, the project lockfile, and selected Agent targets together. If the local directory or installed Skill exists, stop. Never overwrite an existing directory or Agent target.
> 2. Read [source metadata](https://skilld.dev/api/v1/skills/plannotator/effective-html/html-diagram) once. Use sourceUrl, sourceCommit, skillPath, sourceGone, and license. If the source is gone or its path is missing, stop. If license is null, read licence files at the source commit.
> 3. Fetch only the source commit into a temporary Git repository. Do not clone full history. Derive repository_url from sourceUrl, including repository renames. If sourceCommit is absent, resolve the sourceUrl ref once. Set source_commit to that actual commit. Run these commands in one shell call:
>
> ```sh
> git init --quiet "$temporary_dir"
> git -C "$temporary_dir" fetch --quiet --depth=1 "$repository_url" "$source_commit"
> git -C "$temporary_dir" checkout --quiet --detach FETCH_HEAD
> ```
>
> Read applicable licence declarations and notices at that commit. If copying is not permitted, report the restriction and stop.
> 4. Inspect source entries together, then copy the directory containing skillPath into `./skills/html-diagram`. Use the user's path if selected. Keep the original SKILL.md, relative links, scripts, binary assets, and executable modes. Exclude .git metadata. Reject symlinks and paths outside the Skill directory. After checking entries, use cp -a where available. A regular source directory needs no custom copy script. Do not save this page wrapper as SKILL.md.
> Preserve author credit, notices, and applicable licence files from repository or parent directories. Add PROVENANCE.md with the Skill page, source URL, actual commit, original path, and licence. Retain any existing PROVENANCE.md and record new provenance separately. Batch source inspection, copying, and provenance work where practical.
> 5. In the project root, run `skilld install ./skills/html-diagram --mode copy --plain`. If skilld is unavailable, use `npx skilld install ./skills/html-diagram --mode copy --plain`. This known command needs no help lookup. Install does not support --json. Use detected Agent targets, or add --agent for the targets the user selected. Install the local path, never the upstream selector. If installation fails, preserve the local copy and report the exact failure.
> 6. Confirm the local lockfile source and installed Agent copies once. Report the local path, actual commit, and Agent targets. After edits, reinstall the same local path. Upstream updates must not replace it. Do not publish or push unless the user asks.

# 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`](../design-artifact/SKILL.md) 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.

Inspect the result at wide and narrow widths. Check label collisions, clipped nodes, edge routing, reading order, keyboard operation, overflow, and every interactive state.

Return the absolute path, the diagram form chosen, and the main simplifications or assumptions.