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

Annotations already declare readOnly/idempotent/openWorld, and the description adds materially new behavior: free-tier daily limits per IP, and a throttling fallback that returns Sonar's stored copy as `{ data, meta }` with `meta.stale: true`, `meta.stale_as_of`, and a `meta.note` to relay to the user. That is exactly the kind of operational detail annotations cannot carry.

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 sentences, each earning its place: what it does and returns, the auth/rate-limit profile, then the stale-data contract. Front-loaded with the core action, no filler.

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?

There is no output schema, and the description compensates by naming the returned fields and the alternate `{ data, meta }` stale shape. Combined with the free-tier caveat, an agent has everything needed to call it and interpret the 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?

Schema description coverage is 100%, so store/country/store_id formats are fully documented in the schema. The description adds only the notion of a 'store ID' and the Android-vs-iOS metadata nuance, so 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 ('Look up a single app by its store ID') and enumerates what comes back (name, developer, category, rating, reviews, installs, price). This clearly separates it from the search-oriented sibling sonar_app_search, which returns many apps rather than one.

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?

Establishes the usage context: single-app lookup keyed by store ID, usable without an API key on the free tier. It also cross-references the workflow ('the storeId returned by sonar_app_search works as-is'). It stops short of explicitly excluding or routing against the near-sibling sonar_get_app, so it is strong context without full when-not guidance.

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