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

Beyond the readOnlyHint/openWorldHint annotations, the description adds two pieces of real operational context: the credit cost ("Costs 5 credits") and the shape of the returned rows (title, developer, icon). It does not cover pagination behavior or whether results are ordered, which keeps it from a 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?

Two tight sentences with zero waste: the core behavior and return shape come first, then the value proposition, then the cost. Every clause earns its place.

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?

With no output schema, the description usefully names the returned fields and discloses the credit cost, which an agent needs to judge whether to call it. What remains missing is minor: result ordering and how many similar apps typically exist, neither of which blocks correct invocation.

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 the enum for store, the ISO country format, the limit bound, and the app_search fallback for package are all already documented in the schema. The description adds no parameter detail beyond that, 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?

States a specific verb and resource ("List the apps the store itself considers similar to a given app") and even previews the returned fields. The phrase "the store itself considers" implicitly distinguishes it from keyword-driven siblings like keyword_app_competitors, though no sibling is named explicitly.

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?

"The quickest way to build a competitor set from one seed app" gives a concrete use case, and the package parameter description routes the agent to app_search first when only a name is known. No explicit exclusions or named alternatives appear in the description itself, keeping it short of a 5.

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