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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: plan-gating behavior (403), the connection prerequisite, the meaning of every non-`ready` status value, the warning never to read an empty series as zero, the `reported: false` null-metric convention, and the static-FX approximation caveat on proceeds_usd_approx. That is exactly the behavioral context an agent cannot get from structured fields.

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?

Dense but front-loaded: what it returns first, then constraints, then the status-handling rules. Every sentence carries operational information, though the status paragraph is long enough that a bulleted treatment would scan faster.

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 and five parameters, the description carries the full burden and does so: it describes the returned metrics and breakdown shape, the time-window semantics, the gating conditions, and how to interpret empty or partial results. Nothing an agent needs to call and correctly interpret this tool is missing.

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 app_id, start, end, days and store are all documented in the schema with patterns, defaults and ranges. The description adds no parameter-level syntax or format detail beyond confirming iOS-only data, 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 resource (App Store Connect sales for one of your own iOS apps) and enumerates exactly what is returned: daily first-time downloads, redownloads, IAP units, approximate proceeds, window totals, and a per-country breakdown. The scope narrowing ('iOS only', 'your own apps', 'same numbers as the Performance page') makes it distinguishable from the broader revenue/overview siblings.

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 concrete preconditions and failure routing: requires the Agency plan (403 otherwise) and an App Store Connect connection at /settings/connections, plus the instruction to check `status` before trusting data. It does not name an alternative sibling (e.g. sonar_app_revenue) for the non-App-Store-Connect case, so the when-to-use-this-instead guidance is incomplete.

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