place_at_pixel

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

With annotations already declaring readOnlyHint=false and destructiveHint=true, the description still adds real behavior: the ray-cast fallback chain (plane_z, first scene surface with the object ignored, then the object's own bottom plane), and that size and rotation are preserved. It also discloses the return payload. The destructiveHint=true label is not reconciled with an operation framed as pure translation, which is a small gap, but nothing is contradicted.

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 action, then parameters, then output, then usage — a sensible order. The plane_z sentence is dense and takes a second read, but no sentence is padding; it is verbose without being wasteful.

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 six-parameter mutation with no output schema, the description covers behavior, coordinate conventions, fallback semantics, the return value, and sibling routing. Nothing an agent needs to invoke it correctly 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?

Schema description coverage is 0%, so the description carries the full burden and does: it defines the anchor fraction convention with a default example, pixel as [x, y] with y down, image_size as [width, height], and plane_z as the plane the camera ray intersects. That is the substantive semantics an agent needs for all six 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 first sentence names a specific verb and effect ('Move an object so that a point of its box lands where a picture pixel points'), and the closing line explicitly separates it from siblings (attach, move_to_contact, place_on, match_camera). An agent can distinguish this from the other placement tools without opening any 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?

States the positive precondition ('after match_camera', 'where the photo shows them') and the negative case with named alternatives ('Without a photo use attach, move_to_contact or place_on'). Routing is fully explicit.

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