Do walls block a line?

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

Annotations already mark it readOnly, idempotent, and non-destructive. The description adds valuable behavioral detail beyond that: open doors do not block, and it explains the fallback between Foundry's live canvas test and stored walls. This is exactly the kind of context a caller needs.

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 sentences, tightly written, with the core action and result front-loaded. Every clause adds information: the purpose, the use cases, the wall list, the door exception, and the fallback behavior. No fluff.

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 read-only check with fully documented parameters despite no output schema, the description covers the key behavioral nuances: open doors, the canvas vs stored-wall fallback, and that a list of blocking walls is returned. It stops short of specifying the exact return shape, but this is a minor gap given the simple check semantics.

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 100%, so the input schema already documents all four parameters including tokenId vs x/y and the type enum. The description reinforces the 'tokens or points' concept but does not add meaningful parameter-level detail beyond the schema.

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 opens with a specific verb ('Test whether walls block') and a precise resource ('the straight line between two tokens or points'), then enumerates the use cases (movement, sight, light, sound) and the additional output ('list the walls on it'). This clearly distinguishes it from related tools like find-path or measure-distance.

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 names the intended use cases ('for movement, sight, light or sound'), providing clear context for when to use it. However, it does not explicitly contrast this with sibling tools such as find-path or measure-distance, nor does it state when not to use it.

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