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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety burden is covered. The description adds real value beyond that: the 400 m default radius, the accepted feed-slug pattern for agency ("dash", "vre", "wmata"), accepted place formats, and an explicit grounding constraint against supplementing results from memory. It omits return shape and any behavior on empty results.

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 purpose sentence is front-loaded and the Args block is compact and scannable, and the grounding sentence earns its place as a hard constraint. Minor redundancy: the Args block restates defaults that also appear in the schema, though that is justified given zero schema descriptions.

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 no output schema and a search tool, the description never says what a result looks like (stop names, IDs, distances, agency attribution) or how many results to expect, which leaves the agent guessing about response shape. Inputs and safety profile are complete, so the gap is confined to return-value expectations.

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 0%, so the description must carry all parameter meaning, and it does: place accepts a station name, a stop name, or "lat,lon"; radius_m is in meters with a default of 400; agency is an optional feed slug with concrete examples. That is meaningfully more than the bare schema titles provide.

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?

"Stops and stations within walking distance of a place, across all agencies" gives a specific verb-equivalent (proximity search) and resource (stops/stations), plus a scope note that separates it from agency-scoped or station-detail tools. It does not name a sibling explicitly (e.g. get_station_info, transfers_at), so it stops short of a 5.

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 the purpose: it is the tool for finding nearby stops, and the agency arg hints at narrowing scope. There is no explicit when-to-use / when-not-to-use guidance, no statement of when to prefer get_station_info or transfers_at instead, and no note on what to do if the place string fails to resolve (e.g. fall back to geocode_address).

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