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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description still contributes real behavior: newest-month-first ordering, the returned field set, caller-dependent filtering to issued/paid, a PDF link only once issued, and a null return when invoicing is off. It does not mention pagination or volume limits, which is the main remaining gap for a list operation.

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?

One dense sentence that leads with the resource and then enumerates fields, ordering and edge cases. Every clause carries information; the only weakness is that return-shape detail and the null condition are packed in without visual separation.

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 carries the burden of describing returns and does so: line items, totals in cents, status enum values, PDF link and the null case. Combined with the ordering and visibility rules, an agent has nearly everything needed, short of pagination behavior.

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 is a single parameter, workspaceId, and schema coverage is 100%, so the schema already defines it. The description adds no scoping detail about how workspaceId constrains the result set, leaving this at the baseline for a fully documented single parameter.

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?

Names the resource (a client's invoices) and the shape of what comes back, so an agent can tell it apart from get_invoice or list_requests. It is a noun phrase rather than a verb, but the listing semantics are unambiguous from the field inventory that follows.

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?

There is no when-to-use or when-not-to-use guidance and no named alternative such as get_invoice for a single invoice. The clause 'Clients see only issued and paid ones' describes a visibility rule applicable to callers, not a condition for selecting this tool, so the agent must infer usage from the name alone.

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