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

Even though annotations already indicate a read-only, non-destructive operation, the description adds valuable behavioral semantics: the meaning of each status, when ends_at is omitted, and that status 'none' with only_hobby true means a free account rather than a missing subscription. This goes well beyond the annotations.

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?

The description is dense but every sentence earns its place: scope, response format, ends_at semantics, the free-account caveat, and argument count. It is front-loaded with the essential scope and then provides structured detail.

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 parameterless read-only tool, the description is nearly complete: it documents the response shape, statuses, ends_at behavior, and a key edge case. The only small gap is that the 'only_hobby' field's general meaning is not fully defined outside the specific 'none' case.

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?

The tool takes zero parameters alert, and the schema coverage is 100% (empty schema). The description explicitly states "Takes no arguments," which reinforces the schema and prevents the agent from trying to pass parameters.

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 immediately identifies the tool as returning "the account's plan state — not a site's," which clearly distinguishes it from site-level sibling tools. It also enumerates the exact response shape, making the tool's purpose concrete and unambiguous.

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 description gives a clear scope and an explicit exclusion: it is for the account's plan state, not a site's. It does not name alternate tools, but no direct sibling alternative is obvious, and the exclusion helps an agent decide when this tool is appropriate.

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