Reachable area (isochrone)

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

Annotations already declare readOnlyHint=true, indicating a safe read operation. The description adds value by stating that the tool returns a compact summary (bounding box and reach per direction), which informs the agent about the output format. However, it does not disclose any limitations, permission requirements, or error conditions, which would be expected for a tool with no output schema.

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 two sentences long, front-loaded with the core purpose, and includes an illustrative example. Every sentence is necessary and there is no redundant or extraneous text. It is well-structured for quick understanding.

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 has 5 parameters (2 required) and no output schema, the description covers the basic functionality and return type but lacks details on output structure, error handling, or behavior for edge cases like invalid coordinates. It does not explain the meaning of 'reach per compass direction' or how to interpret the bounding box. The description is adequate but not comprehensive for a tool with moderate complexity.

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% (center, profile, language have descriptions in schema; minutes and kilometers do not). The description compensates by clarifying that minutes and kilometers are mutually exclusive and by providing the unit context. It also reinforces the overall concept of the tool. For the uncovered parameters, the description adds meaningful guidance 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 clearly states the tool's purpose: showing reachable area within a time/distance budget. It uses a specific verb ('shows') and resource ('reachable area'), and gives an example query. However, it does not explicitly differentiate from sibling tools like route or route_matrix, which could be clearer given the context of multiple geospatial 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?

The description includes a usage constraint ('Give exactly one of minutes or kilometers') but provides no guidance on when to use this tool versus alternatives. It does not mention prerequisites, typical use cases, or when to avoid it. Compared to other sibling tools, there is no explicit differentiation or when-not advice.

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