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fenestra-mcp

fenestra-mcp

by richer-richard
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Rust
Local

render_ui

Render a fenestra/1 UI description to an accessibility tree, preview image, and warnings for contrast, labeling, and legibility.

Instructions

Render a fenestra/1 UI description to a typed accessibility tree, a downscaled preview image, and automatic accessibility warnings (contrast, labeling, per-text-node legibility). Read the access tree first; the full-resolution PNG comes back as a resource_link.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "description": "<description>"
    },
    "name": "render_ui"
  }
}

Input Schema

NameRequiredDescriptionDefault
sizeNoWindow size as `WxH` (default `800x600`).
themeNoOptional theme: a `ThemeSpec` object, or `{"preset":"dark"}`.
descriptionYesThe UI description: a `fenestra/1` JSON object.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A3.6/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, description discloses that tool returns a typed accessibility tree, downscaled preview, and automatic accessibility warnings. It also notes that full-resolution PNG comes as a resource_link and advises reading the access tree first. This provides useful behavioral context beyond a simple 'render' statement.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, no redundancy. First sentence lists core outputs, second sentence gives action guidance (read tree first), third clarifies image format. Front-loaded with most important info.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given no output schema, description adequately explains what the tool returns (tree, preview, warnings, resource_link). Siblings suggest alternative rendering/comparison tools, but description is sufficient for an agent to understand the tool's role.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, and the schema already describes parameters completely. The description adds no additional meaning beyond what the schema provides for 'description', 'size', or 'theme'. Baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states verb ('Render') and resource ('fenestra/1 UI description'), lists three specific outputs (accessibility tree, preview image, warnings). Does not explicitly differentiate from siblings like film_ui or match_screenshot, but the purpose is unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance on when to use this tool versus alternatives like film_ui or match_screenshot. No 'when not to use' advice or context about prerequisites. The description assumes the agent knows to use it for rendering, but lacks explicit selection criteria.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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