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

Discloses the case-insensitive behavior of the search, which is a meaningful behavioral trait not conveyed by annotations. However, no annotations exist, so the description carries full burden. It doesn't describe matching semantics beyond fields searched (fuzzy, prefix, substring) or what results return, leaving some ambiguity for the agent.

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 sentences, both load-bearing. The first states functionality and scope; the second provides workflow context tying to sibling tools. Zero waste.

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 2-param search tool with a clear output (list of metros with slugs), the description is essentially complete. It covers what's searched, case-insensitivity, and downstream usage. Minor gap: doesn't describe return ordering or that results may be partial, but these are minor for a discovery-oriented search 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 50% — the 'query' parameter has a meaningful example ('san fran', 'brazil') in the schema itself, and 'limit' has default/max/min constraints documented. The description adds little beyond the schema but examples are provided by the schema, warranting baseline. The description does clarify the query targets name, primary city, and country, adding some semantic value.

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 uses a specific verb ('case-insensitive search') over concrete resources (metro name, primary city, country). It clearly distinguishes itself from siblings by stating it's the way to find a metro's slug before calling get_metro or compare_metros.

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?

Explicitly states when to use this tool ('Use this to find a metro's exact slug before calling get_metro or compare_metros'), providing clear context and a workflow for why search precedes those tools. This effectively scopes its purpose relative to siblings.

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