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

Annotations already declare safe, idempotent, and non-destructive behavior. The description adds value by specifying that the output includes journey options with legs, durations, and modes, and that ambiguous locations trigger disambiguation responses instead of journeys. This enhances transparency 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?

The description consists of two efficient sentences. The first clearly states the tool's purpose, and the second covers input formats and an important edge case. There is no redundant information, and all content earns its place.

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 no output schema, the description adequately explains the return type (journey options with legs, durations, modes). It also covers ambiguous input behavior. While additional details like mode options or real-time data are omitted, the description is sufficient for a journey planning tool.

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% with both parameters having descriptions. The description adds meaningful nuance by elaborating that from/to can be stop names, postcodes, or 'lat,lon' coordinates, and by noting the disambiguation behavior tied to ambiguous inputs. This exceeds the baseline of 3.

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?

Description clearly states the verb 'Plan' and resource 'journey across London transport'. It distinguishes itself from siblings like arrivals, bike_points, disruptions, etc., by focusing on journey planning with flexible input types. The edge case of ambiguous locations is explicitly mentioned, adding precision.

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 clear context for usage: planning a journey across London transport with from/to inputs. It gives guidance on handling ambiguous locations by refining input or using more precise identifiers. However, it does not explicitly state when not to use this tool or list alternatives among siblings.

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