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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive). The description adds beyond them: it discloses the auth model ("calling user's stored Figma token"), the failure mode ("actionable error if Figma is not configured"), and the return shape (image plus a text line with frame name and sizes). That is meaningful context, though render latency/rate behavior is not addressed.

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-loads the core action in the first clause, then packs inputs, return value, auth, and a practical tip. A few details (max 2000, 0.5–4 default 2) duplicate the schema verbatim, which is mild redundancy, but overall it is tight and well-ordered.

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?

For a no-required-param, no-output-schema render tool, it covers inputs, auth, error behavior, and a correctness caveat, which is close to complete. The only gap is the lack of explicit routing against the sibling figma_frame_spec, which shares the Figma domain.

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 100%, so the baseline is 3, but the description earns more: it explains *why* width matters ("e.g. the width of a device screenshot you want to compare against") and that scale "controls how sharp Figma renders it" with default 2, adding intent beyond the schema's bare ranges.

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: "Render one Figma frame (or any node) to a PNG". It adds the reason ("so you can look at the design") and distinguishes itself from the sibling figma_frame_spec by being the image-producing tool.

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 clear operational context: how to obtain the link (right-click → Copy link), the url vs file_key+node_id paths, and a tip about comparing by eye. However, it never names or excludes the sibling figma_frame_spec or visual_compare, so the agent must infer when an image is preferable to a spec dump.

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