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

With no annotations present, the description carries the full burden and does so well. It discloses that the computation is local, requires no network or quota, returns geodesic distance in metres, and that the closest point may lie between vertices. These are non-obvious behaviors that the schema does not convey.

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?

Three sentences, each earning its place: the first states the primary output, the second clarifies a subtle geometric behavior, and the third gives a use case and performance characteristic. Information is front-loaded and there is no redundant filler.

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 simple two-parameter geometry calculation, the combination of a 100% documented schema, an output schema, and a description covering purpose, behavior, units, and execution context is complete. An agent has enough information to select and call the tool correctly.

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?

The input schema documents both parameters fully with descriptions of the coordinate and polyline, so schema coverage is 100%. The description adds contextual framing ('coordinate' and 'polyline') but no additional parameter-level meaning beyond what the schema already provides, so the baseline of 3 is appropriate.

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?

Clearly states what the tool does: finds the closest position on a polyline to a given coordinate and returns the geodesic distance in metres. The added detail that the result may fall between vertices, not only on them, helps distinguish it from simpler point-in-polygon or point-to-point distance tools.

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 a concrete use case ('how far is this address from the route?') and highlights that it is a local computation with no network call and no quota, which helps an agent decide when to prefer it. It does not explicitly name alternative tools or state when not to use it, but the context is clear enough.

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