Use as mask

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

Annotations already declare mutating, non-destructive, idempotent behavior, and the description adds real context beyond them: masks crop the layers ABOVE in the same parent, ordering matters, grouping is needed, and editor support is Design (unverified FigJam/Slides). It does not contradict the annotations.

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 purpose, then the critical ordering/grouping caveat, then maskType values, then editor availability — each sentence carries distinct information. Slightly dense but no filler.

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?

Covers purpose, the non-obvious ordering requirement, maskType detail, and environment support. With no output schema and no return-value contract needed, the only untouched items (session, idempotencyKey) are already fully described in the schema, so it is complete enough to call safely.

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 60%, and the description compensates by explaining maskType semantics beyond the raw enum — alpha (default), vector defined as 'the shape's outline', luminance — and implies the isMask toggle via 'stop it being one'. It does not address session or idempotencyKey, but those are already documented in the schema.

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 action on a specific resource — 'Make a shape a mask (or stop it being one)' — including the toggle direction, so an agent knows both what it sets and how to undo it. No sibling in the list performs masking, so no further differentiation is required.

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 strong operational context: place the mask BELOW the layers it crops and group them via figma_group_nodes to keep it local, which tells the agent how to invoke it correctly. It does not state when-not-to-use or name an alternative, but no competing mask tool exists, so the practical guidance is adequate.

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