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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description adds two things the structured data cannot: the cost ('Costs 6 credits') and the interpretation rule that a rank of 0 means the app is not in the results. It does not describe pagination or how many rows come back by default, but the added cost and result-semantics detail are genuinely useful.

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?

Four short sentences, each earning its place: what it does, why it is the direct answer, the prerequisite resolution path, and the zero-rank interpretation. The core scope statement is front-loaded and nothing is padded.

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 four-parameter read-only lookup with no output schema, the description covers purpose, identification path, cost, and one key return-value convention. The remaining gap — the shape of returned rows (keyword, rank, volume, etc.) — is minor given the flat schema and would be the only addition needed to reach full completeness.

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%, including the enum for store and the ISO country constraint, so the baseline is 3. The description only restates the package-id framing and repeats the app_search resolution note already present in the package parameter's schema description, adding no new format or edge-case guidance.

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 — lists the keywords an app is recommended for / ranks on, scoped by store and country and identified by package id. The phrase 'The direct way to answer "what keywords does this app rank for?"' makes the intent unmistakable and separates it from keyword_suggestions and keyword_top_apps, which operate on keywords rather than on an app.

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?

Gives an explicit prerequisite/alternative path: 'If you only have the app name, call app_search first to resolve it.' That routes the agent correctly at the point of ambiguity. It stops short of stating when NOT to use this versus keyword_app_metrics_rankings or keyword_app_competitors, so no exclusions are offered.

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