ap_set_brush

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

With no annotations, the description carries the behavioral burden and does well by revealing that these are direct context writes, immediate in effect, and that omitted values are preserved. It does not discuss potential failure states or prerequisites, but the disclosed partial-update semantics are valuable.

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 short sentences front-load the action and immediately explain the two most important behavioral nuances: partial updates and immediate application. No filler or repetition of schema details.

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 simple context setter, the combination of the explicit schema and the description covers what values to provide and how they apply. It could be more complete by noting prerequisites such as requiring an active painting context, but nothing critical about the core behavior 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 covers all 6 parameters with ranges and units, so the baseline is 3. The description adds meaningful merge semantics beyond the schema by stating that omitted values are left alone, which matters for a tool with zero required parameters.

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 names a specific verb and resource ('Set brush parameters on the painting context') and is distinct from painting-execution siblings like ap_paint_stroke and ap_paint_stroke_world. It also clarifies the scope of the operation as context configuration, not a stroke operation.

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 gives clear temporal context ('take effect immediately for the next stroke'), which implies it should be called before painting. It does not explicitly name alternatives or when-not-to-use conditions, 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.