Claude Slides runs on a closed HTML subset, not free code

Anthropic's announcement sits inside a broader consolidation: Claude Cowork, previously a separate workspace, was merged into the normal Claude chat under the framing of "One Claude," so users no longer choose between chatting and working. The editorial team went past the announcement and wrote files directly from the developer-facing environment that powers the feature, generating a four-slide deck from rough meeting notes. Each slide turned out to be a single HTML file, and the whole deck a single JSON index.

The internal design is unusual in where it puts the constraint. Allowed CSS properties are a fixed list, and the values each may take are limited to px ranges, enumerated keywords, or hex/rgb/hsl colors; margin, float, grid-template-areas, :hover, and keyframe animations are excluded. Custom tags such as <x-shape>, <x-icon> and <x-connector> replace freehand SVG drawing, and SVG itself is capped at 52KB with scripts banned and local references only. Contrast is specified numerically — 4.5:1 for body text against the background, 3:1 for large text — and typography is limited to 4–5 reusable sizes and at most four typefaces per deck, usually two.

The trade-off is legible: expressive range is narrowed so that every output fits the canvas and follows the same visual rules, which is coherent with producing internal, standardized materials in volume. The main open question is whether that design survives contact with the real product — the team could not open the chat UI, so response speed and Japanese rendering quality are unconfirmed, and the ChatGPT Canvas contrast is explicitly framed as inference from public behavior rather than verified internal access.