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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description goes further by disclosing the default range (current month), inclusive bounds, and what the result contains (paid vs unpaid split, per-month breakdown) — valuable since no output schema exists. It omits edge behavior such as invalid or inverted ranges and empty results.

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 short sentences, front-loaded with what the tool returns, followed by scoping detail and then purpose. Every sentence adds information and there is no filler.

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 simple two-parameter, annotation-covered read tool with no output schema, the description supplies the defaults, date semantics, and result shape an agent needs to call it correctly. Minor gaps are edge-case handling and an explicit statement of which invoice states are counted beyond 'issued'.

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 0% and neither parameter is described in the schema, so the description carries the burden — and it does: it supplies the YYYY-MM-DD format, states the range is inclusive, and specifies the current-month default when dates are omitted. It never explicitly maps which bound is 'from' vs 'to', which is the only remaining ambiguity.

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 concrete resource and output ('Sales and VAT totals for issued invoices') plus the scoping dimension ('date range'), which clearly separates it from list-oriented siblings like list_unpaid_invoices. It does not name a sibling to contrast with, so it falls short of a 5.

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?

'Useful for VAT return preparation' gives a real use context, implying this is the reporting tool rather than the listing tools. However, there is no explicit guidance on when to prefer it over list_unpaid_invoices or how to handle cases needing invoice-level detail, so usage is only implied.

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