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

With readOnlyHint and openWorldHint already declared, the description adds genuine non-schema context: the operation costs 5 credits, and the result is framed as the ordered SERP users actually see. It omits pagination/size behavior, but the cost disclosure is the kind of 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?

Two tight sentences: the definition comes first, the use case and cost follow. Nothing is redundant with the title and nothing is wasted.

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, so the description must convey the return shape — 'the search results a user sees' implies a ranked app list, which is adequate. Combined with the cost note, only the limit/paging implications of the optional limit param are left implicit.

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%, with each parameter documented in-schema including store enum values, ISO country code, and a keyword example. The description adds no parameter-level meaning beyond restating store/country/keyword, so the 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?

The description gives a specific verb and resource ('List the apps that rank highest for a keyword in a store/country') and clarifies it means 'the search results a user sees.' That framing distinguishes it from metric-style siblings like keyword_metrics, though it never names keyword_app_competitors or app_search, which intuitively overlap.

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?

'Use it to find the incumbents / competitors for a keyword' gives a positive usage context, but there are no exclusions and no routing to alternatives, even though keyword_app_competitors sounds like it addresses the same need. The agent is left to infer which of the two to pick.

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