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

Annotations only declare readOnlyHint and idempotentHint, but the description adds rich behavioral details: accent-insensitive matching, every-word-must-match semantics, sorting by renown with route-name matches first, no-query behavior, and the output format (compact per-route facts with id and URL). No contradiction with 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?

Three dense sentences with no filler. The first sentence establishes scope and filters, the second covers matching and output, and the third gives usage guidance. The structure front-loads the key information.

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 search tool with no output schema, the description covers what fields are matched, how filtering works, result format, sorting, no-query behavior, and provides follow-up tool suggestions. The only remaining detail (limit constraints) is already in the schema. Complete enough for an agent to use correctly.

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 100%, but the description significantly enriches parameter meaning by explaining matching semantics (accent-insensitive, every word must match), sorting behavior, and that omitting the query browses all routes. This goes beyond the schema's property descriptions.

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 this is a free-text search over every atlas route, enumerates the matched fields (name, cities, train name, operator, countries), and lists optional filters. It distinguishes itself from siblings by explicitly pointing to get_route, famous_routes, and city_pair for other use cases.

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 explicitly says when to use this tool and names alternatives: use get_route for full detail, famous_routes for a ready-made top list, and city_pair for A-to-B journeys. It also explains no-query behavior. However, it doesn't mention the sibling routes_in_country or night_trains, so it's not fully exhaustive.

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