| name | html-artifacts |
| description | Produce a self-contained HTML artifact instead of a markdown document when the request is for content that benefits from spatial layout, color, real diagrams, interactivity, or a round-trip editor. Use this skill aggressively whenever the user asks for a "doc," "writeup," "plan," "spec," "report," "explainer," "summary," "comparison," "review," "PR description," "mockup," "diagram," "flowchart," "deck," "slides," "status update," "post-mortem," "incident report," "playground," or a one-off "editor" or "tool" for triaging/reordering/tuning anything — even if they don't explicitly say "HTML" or "artifact." Also trigger when the user asks Claude to "explain," "summarize," "compare," "explore options for," "brainstorm directions for," or "walk through" a non-trivial topic. Stay in markdown only for short conversational replies, code-only outputs, terminal-style command answers, and content that's genuinely just a few sentences. |
HTML Artifacts
Markdown is the default agent output, but for anything longer than a handful of sentences it's a poor format. It can't show two options side by side, can't render a real diagram, can't be interactive, and can't be shared by link. HTML can do all of those — and when the artifact is the deliverable rather than something you'll skim and forget, the difference between "a document I'd skim" and "a document I'd actually read" is enormous.
The use cases below are not the only places HTML helps, but they cover most of the territory. The pattern in every category is the same: the agent picks a layout that makes the shape of the content visible, instead of flattening it into linear prose.
When to reach for HTML
Reach for HTML when any of the following is true. Don't wait for the user to ask explicitly.
- Comparison. Two or more options/approaches/designs the reader needs to weigh against each other. Side-by-side beats stacked.
- Spatial information. Diffs, call graphs, module maps, flowcharts, timelines, before/after — anything where position carries meaning.
- Interaction matters. Animations, easing curves, parameter tuning, state transitions — things the reader needs to feel, not read about.
- Reference material. A document the reader will navigate non-linearly: tabs, collapsible sections, glossary in the margin, jump links.
- Color or hierarchy carries meaning. Severity tags, status colors, syntax highlighting, design tokens.
- One-off editor. The reader needs to manipulate a thing (drag tickets, toggle flags, tune a prompt) and round-trip the result back into a prompt or a commit.
- The reader will share it. A spec going to leadership, a PR writeup going to reviewers, a status report going to a team. People are dramatically more likely to actually read an HTML page than a markdown file.
- Length. Anything longer than ~100 lines in markdown becomes hard to read. HTML's navigation and layout earn their keep past that threshold.
The heuristic, said another way: if the user is going to do something with the document — read it carefully, share it, refer back to it, hand it to an implementer, paste edits back in — make it HTML.
When to stay in markdown
Markdown still wins for:
- Short conversational replies inside chat.
- Code-only outputs (a function, a config block, a one-liner).
- Terminal/command-flavored answers ("run this, then that").
- Quick three-bullet summaries the reader will scan once and discard.
- Files that need to be diffed in version control regularly. HTML diffs are noisy. If the artifact will live in git and be reviewed in PRs over time, markdown is friendlier — though even then, generating an HTML view alongside is often worth it for review.
If the artifact is going to be edited by hand by a human afterward, markdown is also friendlier. But increasingly artifacts are edited by re-prompting Claude, which removes that advantage.
Universal rules for every HTML artifact
Every artifact this skill produces must satisfy all of these:
- Single self-contained
.html file. No build step, no bundler, no npm install. CSS goes in a <style> tag, JS goes in a <script> tag, images are inline SVG or data URIs.
- Works offline. No required network calls at view time. If a CDN is used (Tailwind, a font, a library), prefer well-known stable CDNs and assume the user might want to swap to inlined later. For Claude Code outputs that may be archived or shared via S3, lean toward fewer external dependencies.
- Mobile responsive. Include
<meta name="viewport" content="width=device-width, initial-scale=1"> and a layout that survives a narrow viewport. Greg or anyone else may open it on a phone.
- Real layout, not stacked headers. If the content is a comparison, lay it out in columns. If it's a timeline, draw a timeline. If it's a diff, render a diff. Don't translate markdown structure 1:1 into HTML — that's wasted effort.
- Readable on its own. Title at the top, a one-paragraph TL;DR or framing sentence right below, then the substance. The reader should know what they're looking at within five seconds.
- Tasteful by default. A neutral but considered design: legible serif or sans body, comfortable line length (60–75ch), generous spacing, restrained color, dark-mode-friendly if cheap. Resist the default-AI aesthetic of "everything is a card with a gradient." See
references/matching-your-style.md if the user has an existing design system to match.
- Editors export back to text. This one is non-negotiable for any artifact where the reader manipulates state. The artifact must end with a "copy as markdown" / "copy as JSON" / "copy as prompt" button that turns the UI state into something pasteable. The whole point of a throwaway editor is the round-trip.
Category index
Pick the matching reference file below before drafting. Each one has the per-category pattern (what the layout should look like, what's load-bearing, what mistakes to avoid) plus a sketch of a concrete example.
| If the request is about… | Read… |
|---|
| Brainstorming options, side-by-side comparisons, implementation plans, exploring directions before committing | references/exploration-and-planning.md |
| Annotated diffs, PR writeups, code review, module maps, "explain this code" | references/code-review-and-pr.md |
| Design systems, component sheets, mockups, prototyping animations or interactions | references/design-and-prototypes.md |
| Inline SVG figures, flowcharts, architecture diagrams, technical illustrations | references/diagrams-and-illustrations.md |
| Status reports, incident timelines, post-mortems, concept explainers, feature deep-dives, learning material | references/reports-and-research.md |
| Slide decks, arrow-key presentations | references/decks.md |
| One-off custom editors: triage boards, flag toggles, prompt tuners, dataset curators | references/custom-editors.md |
| Matching the user's existing visual style or design system | references/matching-your-style.md |
If the request spans multiple categories (e.g., "implementation plan with mockups and a flowchart"), read all the relevant references. They're short.
Output mechanics
Two environments, slightly different mechanics.
In Claude Code
Save the file to the working directory with a descriptive kebab-case name and a .html extension. Examples: onboarding-design-explorations.html, pr-streaming-review.html, cycle-14-triage.html. After saving, tell the user the path and offer to open it in their default browser (open <file> on macOS, xdg-open <file> on Linux). For shareable artifacts the user may upload to S3, Notion, etc. — that's their call, but mention the option once.
If the artifact is a member of a web of related files (explorations → mockups → plan), put them in a folder together so they can be opened/shared as a unit.
In Claude.ai
Use the artifact system. Output a single HTML artifact (text/html) — not React, not Mermaid, not SVG-only — unless the request specifically calls for one of those. The HTML artifact is the closest analog to what Claude Code would produce on disk and gives the user the same affordance: open, screenshot, share.
For Claude.ai's artifact environment, observe the platform's rules: no localStorage/sessionStorage (use in-memory state), no external script tags that aren't on the allowed CDN list, and the artifact must work as a single file.
A note on token cost and time
HTML artifacts cost roughly 2–4× the tokens of a markdown equivalent and take longer to generate. This is a real tradeoff. The skill is configured to err toward HTML because the reading experience is dramatically better and shareability matters, but if the user is iterating fast on something disposable ("just summarize what's in this file"), a markdown reply is fine. Don't manufacture a use case for HTML where there isn't one.
A note on taste
Bad-looking HTML is worse than good markdown. If the artifact would render as a wall of generic Tailwind cards with emoji headers, slow down. Read references/matching-your-style.md first. If the user has a frontend-design skill or design system file in the repo, lean on it. If not, default to a calm typographic layout — system serif body, restrained palette, real structure — rather than a busy "dashboard" look.
A note on what this skill is not
This skill is not "always answer in HTML." The point is not the format; the point is that for many of the things people ask agents to produce — plans, comparisons, reviews, explainers, editors — the format markdown forces (linear text, no spatial layout, no color, no interactivity) actively obscures the content. HTML lifts that constraint. Where markdown is genuinely the better medium, use markdown.
