set_material

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

Annotations already declare this is a non-read-only, idempotent, non-destructive write. The description adds behavior annotations do not carry: a missing material is created with the supplied color, while an existing material retains its color unless update_existing=true. It also surfaces the blast radius of recoloring (every entity using that material), which is important given destructiveHint=false.

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 tight sentences with the core action front-loaded and the conditional color/update rule immediately after. No filler, and the parentheses efficiently carry the default-selection behavior.

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 5-parameter mutation tool with no output schema and 40% schema coverage, the description covers the material/color/update_existing semantics well but says nothing about back_too or what the call returns. Adequate, with a visible gap on one parameter.

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 only 40%, so the description must carry weight, and it does explain the interaction between color, material, and update_existing. However back_too and the exact format of entity_ids/color are left entirely to the schema, which only partially documents them.

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?

Names a specific verb+resource (apply a material) and the target scope (entity_ids or current selection), which is enough to tell it apart from list_materials and from the analogous set_tag. It stops short of explicitly contrasting itself with sibling setters, so it lands at 4 rather than 5.

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 parenthetical '(entity_ids or the current selection)' implies the two invocation modes and the empty-list default, which is real usage guidance. There is no statement of when not to use it or which sibling to prefer for related operations, so usage is only implied.

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