Change walls, lights and other canvas elements

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

Annotations already indicate destructive and idempotent behavior. The description adds specific guarantees: all IDs are checked first (one unknown ID changes nothing) and fields already holding the value are not written, which explains the idempotency. It also adds the 'change' scene permission requirement. This goes beyond the annotations without contradicting them.

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 description is a single dense paragraph that front-loads the core action and limit, then provides format, atomicity, and permission details. It is compact and avoids redundancy with the schema, though it could be slightly more structured.

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 mutation tool without an output schema, the description covers key operational aspects: element type, update format, limits, atomic validation, permission, and behavior on unchanged fields. It does not describe the return value, but that is a minor gap given the rich annotations and the clarity of the operation.

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 parameters are already documented. The description adds useful semantics: it clarifies the structure of the updates array as { id, changes }, gives an example of Foundry fields ('config.dim'), and references create-canvas-elements for wall format. This adds meaning beyond the schema's repetitive description.

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 states a specific verb ('Change') and resource ('up to 200 elements of one type on a scene'), and clarifies it updates existing elements. It is clearly distinct from sibling tools like create-canvas-elements or delete-canvas-elements based on the wording and scope.

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 description implies usage by saying 'Wall words as in create-canvas-elements', referencing a sibling for format, and notes the required 'change' permission level. However, it does not explicitly state when to use this tool instead of alternatives or when not to use it, leaving some choice implicit.

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