Set an instance’s properties

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

Annotations already mark this as destructive, and the description adds useful behavioral details: it mutates the existing instance, tolerates keys missing their id suffix, and refuses invalid keys by returning the list of valid ones. No contradiction with annotations is present.

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 sentences in the first paragraph carry the core behavior and validation rules, and the second paragraph gives a helpful analogy to create_instance. It is efficient and front-loaded, though the analogy could be trimmed without losing essential content.

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 mutating instance-property tool with only two params, the description covers what the tool changes, where to get valid keys, how key matching works, and how failure behaves. The nodeId omission behavior is handled in the schema, so nothing critical is missing.

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 describes both parameters well, so a 3 is the baseline, but the description adds meaningful semantics: properties should use keys from figma_component_properties, variant values are option names, booleans are true/false, and text properties are strings. This enriches what the schema alone provides.

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 description clearly states the tool sets an instance's variant, text properties, and boolean properties. It also distinguishes itself from placing a component (figma_create_instance), so an agent can tell exactly what this tool does beyond its name.

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?

It explicitly instructs the agent to take keys from figma_component_properties, explains id-suffix matching behavior, and says what happens when a key matches nothing. It also names when to use this instead of figma_create_instance, making the usage boundary unambiguous.

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