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

Annotations already declare the operation as read-only, idempotent, and non-destructive, so the safety profile is already covered. The description adds behavior that the annotations cannot express: this build returns no records and is gated behind phase 2, which prevents wasted calls and explains an empty result. It stops short of saying whether a future build will accept filters or pagination.

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 short clauses, both of which earn their place: one identifies the resource and the other states the availability constraint up front. There is no filler, no repetition of the schema, and no hedging.

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 no-argument stub with no output schema, the description covers the essentials: what the tool will do and why it currently yields nothing. It does not say what fields an invoice record will eventually contain or when phase 2 lands, though both are moot while the tool is inert.

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?

There are zero input parameters, so there is no parameter meaning to document; the empty schema is fully self-describing. This dimension is a baseline case rather than a strength of the description.

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 states a specific verb and resource ('Lists customer invoices'), which is clear enough to distinguish it from unrelated siblings like whoami or request_appointment. However, it does not differentiate itself from the closely related get_invoice, list_billed_time, or list_subscriptions, so an agent must infer the distinction from the names alone.

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 strong negative signal, that this tool is unavailable and returns no records, which effectively tells the agent not to call it. It never names an alternative for retrieving a single invoice (get_invoice) or points the agent anywhere else, so the guidance is only half complete.

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