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

The annotations already mark readOnlyHint as true, so the description only needs to add behavioral context. It adds the useful scoping detail ('across the site, or for one account') and the exact GET endpoints, but it does not describe pagination behavior, response shape, or any operational caveats. This is consistent with the annotation, not contradictory.

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 two short sentences with no fluff. The core action and main scoping behavior are front-loaded, and the endpoint reference is useful without bloating. Every piece of text 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?

For a read-only list operation with 100% schema coverage and no required parameters, the description provides enough context: the action, scoping options, and endpoints. The lack of an output schema is mitigated by the predictable list semantics and the algorithm's existing Recurly API knowledge.

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 parameter descriptions already carry the full meaning for sort, type, limit, order, state, time bounds, and account_id. The description only re-itirates the account_id scoping concept already present in the schema, adding no new parameter semantics.

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 begins with a specific action and resource ('List invoices'), then immediately clarifies the scope: across the site or for one account when account_id is given. It also cites the Recurly endpoints, making the operation unambiguous and clearly distinguishing it from sibling tools that list accounts, plans, or subscriptions.

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 clear context for the two usage modes: site-wide listing vs. account-scoped listing triggered by account_id. It does not explicitly name alternative tools or state when not to use this tool, but the siblings are distinct resources, so confusion is unlikely.

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