HTML

• Any session output becomes one self-contained, Artifact-safe HTML file that makes zero external requests and renders for the owner.
• Layout, typography and color come entirely from Tools/Render.ts registers; the model supplies only typed content JSON, so no hand-styled one-off ships.
• The artifact is verified before hand-off — published through the Artifact tool and pixel-checked.

No user configuration: registers are defined in Tools/Render.ts, which embeds fonts found in ~/Library/Fonts, /Library/Fonts or /System/Library/Fonts/Supplemental (macOS font folders; with none present it falls back to system font stacks). Publishing needs the Claude Code Artifact tool and its artifact-design skill; without them Render.ts still writes the local HTML file.

• DOM-render screenshot pipelines drop CSS pseudo-element generated content (counters, ::before labels render in the browser but vanish from DOM-render captures, and they're invisible to text extraction). Render.ts therefore emits all numbering and labels as real DOM text. Never add CSS counters to a register. (Discovered 2026-07-11.)
• Artifacts block all external requests — a Google Fonts <link> fails silently and you get the fallback stack. Embed via data-URI @font-face (Render.ts does this when the register's font file exists locally) or design on system stacks.
• The artifact viewer wraps your file in its own document skeleton — emit <title> + <style> + body content only; no <!doctype>/<html>/<head>/<body> tags.
• A published artifact is private to its owner's claude.ai account — verifying it in a browser signed into a different account/org 404s. Verify the render by serving the HTML file locally and capturing that; verify publication via the Artifact tool's list action.
• Numbered section markers must mean something. Render.ts numbers sections (document order — legitimate). Don't number list items unless the content is a true sequence; use list blocks with bold lead-ins instead.

Example 1: After a research or red-team session

User: "/HTML"
→ Render intent
→ The session's findings, quotes and sources are published as a `dossier` artifact, its local render pixel-checked, and the URL handed over with a one-line description

Example 2: Different subject, different register

User: "render the quarterly cost analysis as HTML"
→ Render intent
→ A `ledger` artifact with tables and callouts, the register that fits a cost report