draw_arc

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: it discloses units (mm), arc direction (counter-clockwise in sketch coordinates), two mutually exclusive construction modes (through a point or around a center), and the geometric constraint that start/end must be equidistant from the center. It omits prerequisites such as needing an active sketch/document and how failures surface.

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?

Front-loaded with the core action and a usage example, then a compact Args block that adds meaning rather than restating names. No filler sentences.

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 10-parameter geometry tool with no annotations and an output schema, the description covers the drawing semantics, modes, units, and direction well. It could add the context that a sketch must be active and note that xm/ym and cx/cy are optional alternatives, but nothing essential to invoking it correctly is absent.

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 only 10%, so the description must compensate, and it does: x1/y1/x2/y2 are start and end, xm/ym is a point on the arc between them, cx/cy is the center with the equidistance constraint, and sketch_index 0 means the latest sketch. Only 'instance' is not explained here, but the schema itself documents it.

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 ('Draw an open arc from (x1, y1) to (x2, y2) in mm') plus a concrete use case (closing a profile drawn with draw_line). It also explicitly distinguishes itself from the sibling draw_closed_profile, so the agent can separate the two without inspecting schemas.

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?

Gives explicit routing: use this for open arcs, e.g. to close a draw_line profile, and 'For closed shapes prefer draw_closed_profile.' That names the alternative and the condition selecting it, leaving little to inference.

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