create_gp_material

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

With no annotations, the description carries the full burden; it does add real behavioral context by disclosing the version-specific fill restriction and by describing the return value. It stops short of stating whether an active Grease Pencil object is required, whether the material is auto-assigned, or whether repeated calls create duplicates — significant for a creation tool.

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?

The core statement is front-loaded in a single sentence, followed by the constraint and then Args. The Returns line is largely redundant given an output schema exists, which is the only small piece of waste.

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 two-parameter creation tool with an output schema, the definition covers the resource, the parameter formats, and an important behavioral caveat. What is missing is the object-context requirement for a Grease Pencil material, which would matter operationally.

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 description coverage is 0%, so the description must compensate, and it does: it defines `name` as the material name and `color` as a four-component stroke RGBA with components 0.0–1.0, which the bare schema never says. It omits the black default (0,0,0,1) but that is visible 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 verb and resource ("Create a Grease Pencil material") and narrows the scope to the stroke colour, which separates it from the generic create_material / create_principled_material family. It never names a sibling explicitly, so the differentiation is inferable rather than stated.

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 fill limitation ("Fills are not offered: in Blender 5.2, strokes built from a script do not render their fill") is a genuine when-not-to-use signal that usefully bounds expectations. However, there is no guidance on when to reach for this tool versus create_material, assign_material, or create_grease_pencil — the agent must infer usage from context.

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