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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the description only needs to add context — and it does, disclosing the return shape (citable peak IDs and URLs) and the semantics of an empty result set. It stops short of noting result-count limits or ranking behavior, which keeps it at 4 rather than 5.

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 tight sentences: capability first, then sibling routing, then the empty-result caveat. Every sentence carries distinct information and nothing is repeated.

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 one-parameter search tool with an output schema and rich annotations, the description supplies everything an agent needs: what to put in, what comes out, which sibling to prefer, and how to read a null result.

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?

The single query parameter is fully documented in the schema (100% coverage), including length bounds and an example. The description restates the same facets in near-identical wording, adding only the slightly broader 'climbing request' framing, so the schema is doing the heavy lifting.

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 (search) and resource (peaks.fyi catalogue) plus the accepted query facets: name, alternative name, country, range, or free-form climbing request. It also names what comes back (citable peak IDs and URLs), which lets an agent distinguish it from fetch and search_peaks without opening a schema.

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 routes the agent: use fetch to read a result, use search_peaks for explicit filters and pagination. It also pre-empts a common misinterpretation by stating that an empty result means no match in this catalogue, not that the mountain does not exist — a real when-not-to-conclude rule.

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