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

Goes well beyond the readOnly/destructive annotations: explains that SANDBOX environments mean test purchases underpin the verdict, that cancellation only flips will_renew while access persists to expires_at, and that unknown users return 'none' instead of erroring. This is exactly the non-obvious behavior an agent needs.

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?

Front-loads the verdict definition, then packs three valuable caveats into one dense sentence. No filler, though the multi-clause sentence is slightly heavy to parse.

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 still surfaces the key response fields (environment, will_renew, expires_at) and the unknown-user case, so the agent knows what to expect. It doesn't enumerate the full return shape, but it covers what matters for correct use.

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?

Only one parameter (`user_id`) with 100% schema coverage, so the schema already documents it as a device, account, or RevenueCat id. The description says 'one user' but adds no format or resolution detail beyond the schema — baseline 3.

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 — 'authoritative paid/not-paid verdict for one user' — and names the unified backends plus the REST endpoint it mirrors. An agent can immediately distinguish it from get_user or get_analytics without opening a schema.

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 decision guidance: always inspect `environment` before granting production access, and treats unknown users as a valid 'none' rather than an error. It doesn't name a sibling as an alternative, so it falls just 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.