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

No annotations, so the description carries the burden and does well: it discloses that a host must have a native render lane, that the reply is NOT an McpResponseEnvelopeV1 with no released contract, and what the return contains (first frame, live-frame token, node ids). Still silent on failure modes, timeouts, or stream lifecycle beyond the token.

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

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

Front-loaded with the core action, but it is dense and packs stream mechanics, host requirements, contract caveats, and downstream-consumption notes into one paragraph. Some of this could be trimmed, and the sibling-differentiation clause is buried mid-sentence.

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

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

Given an output schema exists, the description needn't explain return values in full, yet it usefully flags the non-standard reply shape. It covers host prerequisites and the downstream catalog_get_preview_data linkage, leaving only error/stream details unstated.

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

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

Schema coverage is 67%; the token and revision params are already documented in the schema, including the header-vs-body preference. The description adds no per-parameter meaning beyond noting that node ids feed catalog_get_preview_data, so baseline 3 is appropriate.

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

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

States a specific verb and resource ('Compile a design and render it with real Compose on this host') and explicitly distinguishes itself from the browser/Wasm path and from catalog_render_preview by naming the native render lane. An agent can select this over sibling render tools without opening schemas.

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

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

Gives a clear purpose-based context ('the way to see what a design looks like on Android') and implicitly routes to catalog_get_preview_data for bounds. However, it does not state when NOT to use it versus catalog_render_preview / catalog_render_matrix, so selection among render siblings is left partly to inference.

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