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

Annotations already mark the tool as read-only and idempotent, so the description only needs added behavioral context. It provides useful behavior beyond the schema: a place aggregates all stations and airports, and typing a station code like 'CSMT' resolves to its city while reporting which terminal matched. This gives the agent a strong mental model of how results are grouped.

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 front-loaded with the core purpose and the critical usage instruction, followed by a concise explanation of the place concept and a concrete example. Every sentence earns its place with no fluff or redundancy.

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 read-only lookup with two parameters and no output schema, the description is largely complete: it explains input semantics, output-level behavior (city plus matched terminal), and how the tool fits before plan_journey. It could mention limit behavior or empty-result handling, but these are minor gaps given the tool's simplicity.

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 coverage is 50%: the query parameter is described in the schema, but limit is not. The description adds value by showing station-code input works and that the result is city-level with terminal matching, but it does not explain the limit parameter or its effect on results. This partially compensates for the schema gap but does not fully cover it.

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 uses a specific verb and resource: it 'turn[s] what somebody typed into RailRoute place ids'. It clearly distinguishes this lookup/geocoding tool from journey-planning and station-info siblings by explaining that a place is a city with stations and airports.

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 gives explicit usage context: 'ALWAYS call this before plan_journey.' This tells the agent when the tool is needed in the workflow. It does not, however, explicitly state when to choose an alternative like nearby_stations instead, so it stops short of full exclusion guidance.

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