Reachable area (isochrone)

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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, covering safety and idempotency. The description adds behavioral detail about the return format: 'a compact summary of the reachable area: bounding box and reach per compass direction.' It also discloses the exclusivity constraint on minutes/kilometers, which is not in the schema. This is valuable context beyond annotations.

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 with zero waste. The main purpose is front-loaded, followed by an example, output summary, and a crucial constraint. Every sentence serves a purpose, and the description is compact and easy to parse.

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?

Given the tool's moderate complexity (5 params, 2 required) and the presence of an output schema (which covers return details), the description covers the essential usage and output summary. It does not discuss error handling or edge cases like invalid coordinates, but that is not expected for a well-documented tool. The constraint on minutes/kilometers is clearly stated. It is sufficiently complete for an agent to call it 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?

Schema description coverage is 60%, with minutes and kilometers lacking descriptions. The description clarifies these as mutually exclusive budget parameters ('time or distance budget') and gives an example that ties profile and minutes together. It also explains the output meaning, which indirectly helps interpret parameters. This adds meaning beyond the schema, though it doesn't detail all parameters (e.g., language) – but those are already described in 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 states a specific verb ('Shows how far you can get') and resource ('from a place within a time or distance budget'), and gives a concrete example ('what is reachable in 15 minutes on foot?'). This clearly distinguishes it from siblings like route (path) or route_matrix (multiple paths) by focusing on the reachable area rather than a specific route.

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 provides a clear use case with an example and explicitly instructs 'Give exactly one of minutes or kilometers,' which is a critical usage constraint. It does not explicitly name alternatives like route or suggest when not to use it, but the scenario is evident enough for an agent to infer appropriate selection.

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