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

With no annotations, the description carries the burden and does well: it discloses that no raw records are returned, that sums are never mixed across currencies, and that results are grouped by the selected dimension. It omits cost/permission context and what an empty result looks like, keeping it short of a 5.

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?

Three sentences, front-loaded with the core action, then output shape, then the cost rationale. No filler and nothing buried.

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?

There is no output schema, but the description compensates by spelling out the return shape (count plus gross total, taxable base and VAT per currency, grouped by dimension). Slightly short of complete since the exact grouped-result keys and empty-result behavior are unspecified.

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 coverage is 100% and each parameter already documents its semantics (including the 'issued' alias and default), so the baseline of 3 applies. The description reinforces the grouping and currency-restriction concepts but adds no format or edge-case detail beyond the schema.

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 ('Aggregate invoice totals') plus a decisive negative scope ('without returning raw records'), which instantly separates it from the search_* siblings. An agent can tell what it produces (count + per-currency sums grouped by a dimension) without opening the 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?

Explicitly routes the agent away from 'search_invoices + manual aggregation' by framing this as the cheap alternative, which is a real when-to-use signal. It does not, however, distinguish itself from nearby report_* siblings (report_invoiced_by_period, report_vat_collected) that could plausibly overlap.

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