Show it on the canvas

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

The description adds substantial behavioral context beyond the generic annotations: it changes no design data, works without Edits, leaves no undo step, and moves the viewport. It even warns the agent to narrate what it is showing the designer.

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?

Two compact paragraphs with the core action front-loaded. Every clause earns its place: timing, side effects, and a caveat about moving the viewport are all useful and non-redundant.

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 side-effect-only viewport tool with no output schema, the description covers effect, timing, mutation safety, and the viewport caveat. The optionality of nodeId/nodeIds is clear enough from the schema and description.

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?

The schema already fully describes both parameters: nodeId as one node and nodeIds as several nodes up to 20. The description adds no parameter-specific meaning beyond what the schema provides, so the baseline of 3 applies.

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?

The first sentence states a specific verb ('Selects'), resource ('one or more layers'), and the canvas-scroll effect. This clearly distinguishes it from data-mutation and tree-walking siblings like figma_set_fill or figma_get_tree.

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?

The description explicitly prescribes when to use it: before describing a tree-walked node and after an edit. It does not explicitly name alternatives or give when-not-to-use guidance, so it stops short of a 5.

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