fenestra-mcp

A Model Context Protocol server that lets an AI assistant render and verify native UIs described as fenestra fenestra/1 JSON.

Install

cargo install fenestra-mcp

The server speaks MCP over stdio — point your MCP client at the fenestra-mcp binary.

Related MCP server: precision-desktop

Tools

describe_vocabulary — the description grammar: every node type with a minimal example, and the theme color roles a color may name. Call this first.
describe_schema — the formal JSON Schema for a fenestra/1 description, the machine-checkable complement to describe_vocabulary.
render_ui — render to a typed access tree, a downscaled preview image, and automatic accessibility warnings.
query_ui — find nodes by a semantic selector (role, name, value, or id); a miss returns the nearest candidates to guide a retry.
interact — drive scripted interactions (click, type, key, tab, hover, wheel, drag) by semantic selector, never coordinates.
check_a11y — theme contrast, labeling of every interactive control, and per-text-node APCA + WCAG 2 legibility.
focus_order — the keyboard focus order: the refs a Tab cycle visits, in order, honoring a modal focus trap.
check_layout — layout geometry from the real frame: interactive targets below the minimum hit size, and signal-bearing nodes clipped off-screen.
match_aria_snapshot — assert an expected accessibility snapshot (partial / strict / regex).
match_screenshot — compare against a baseline PNG, pixel by pixel, with an optional tolerance, differing-pixel budget, and mask rectangles to ignore.
validate — validate a description without rendering; problems come back path-pointed.
run_scenario — drive a description + optional steps through a whole bundle of expectations (emitted intents, a11y, aria, screenshot, queries) in one pass, asserted against the post-interaction frame.
film_ui — drive optional steps (applied first, so a click can trigger the transition to watch), then capture frames with real motion on and compose them into one captioned filmstrip. The one tool that turns reduced motion off — every other tool stays reduced-motion for deterministic pixels.

Each tool leads with a typed structured result — query_ui, check_a11y, focus_order, check_layout, match_aria_snapshot, and describe_vocabulary carry a formal outputSchema so a client knows the result shape up front. The visual tools also attach a downscaled preview image and a resource_link to the full-resolution PNG (a file:// temp path), so a large image never bloats the response yet stays one fetch away.