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

Annotations already cover readOnly/idempotent/non-destructive, but the description goes well beyond them: statelessness, a 32 KB payload ceiling, a 60 RPM rate limit, demo-access via '?demo=true' or L402 payment of 150 sats, and an HTTP 400 failure mode for invalid input. These are operational facts an agent cannot obtain from the annotations and that directly affect retry and batching behavior.

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?

Purpose and the sibling exclusion are front-loaded, which is the right ordering. The final sentence is information-dense to the point of being a run-on, packing payload cap, rate limit, payment, and error semantics together, but nearly every clause carries operational value an agent needs.

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?

An output schema exists, so the description is not obliged to explain return values. Combined with the annotations covering the safety profile and the description covering limits, access modes, and error behavior, an agent has everything required to invoke this correctly and handle failures.

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 100%, so both parameters are already fully documented, including the coordinate_frame enum and its default. The description only restates the default value ('coordinate_frame' defaults to 'cartesian_xyz_meters') without adding syntax, format, or content guidance for the prompt body beyond what the schema says. Baseline 3 applies.

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 ('Computes') with three concrete output artifacts (3D spatial affordances, obstacle-avoidance waypoints, manipulator grasp sequences) and names the reasoning engine. It also draws a hard boundary against operate_computer_use_agent, so an agent can distinguish it from siblings without opening a schema.

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?

Explicitly enumerates the use cases ('physical robot arm kinematics, mobile navigation waypoints, or spatial scene task orders') and names the correct alternative for the adjacent-but-different case ('2D desktop or browser GUI screens, use operate_computer_use_agent instead'). Both when-to-use and when-not-to-use are given.

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