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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is fully covered. The description adds only the supported service systems, which largely duplicates the city enum, and says nothing about ordering, coverage completeness, or edge cases like a line serving multiple cities.

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 tight sentences, purpose front-loaded and the platform-coverage note following. Nothing is wasted and the reader gets the scope in the first clause.

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?

With an output schema and full annotations, the description needn't explain return values or safety. It is nearly complete for a simple filtered lookup; only the sibling-routing guidance and any ordering/limit behavior are absent.

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%, but the undocumented half is the city enum (dc/nyc), which the phrase 'Supports DC Metro and NYC Subway' maps to real systems — a modest value-add. The lineCode details are already exhaustively documented in the schema, so the description correctly does not repeat them; baseline 3 applies.

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?

States a specific verb and resource ('Get all stations on a specific transit line'), so the agent knows exactly what it returns. It does not explicitly distinguish itself from the sibling get_all_stations or search_stations, leaving the line-filtered scope as the only implicit differentiator.

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?

Usage is implied by 'on a specific transit line' — use this when you know the line and want its full station list. But no explicit when-not or named alternative (get_all_stations, search_stations, get_route_info) is given, so the agent must infer the boundary between siblings.

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