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

Beyond readOnlyHint/openWorldHint, it discloses the default-selection algorithm (ended-and-unfiled, else running quarter), the full state taxonomy with definitions, and the computation formulas for totalVatOwed and netPayableEur including sign meaning. This is substantial behavioral detail an agent could not infer from annotations.

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 core purpose is front-loaded in the first clause, followed by default behavior, state definitions, and formulas. It is dense but nearly every clause carries needed information; the state enumeration and formulas could be slightly tightened but nothing is wasted.

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 compensates by naming the returned fields (state, deadline, figures, otherQuarters, totalVatOwed, netPayableEur) and their semantics. Combined with 100% schema coverage on the two optional params, an agent has everything needed to call and interpret it.

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%, so the baseline is 3, but the description adds real semantic value: it explains what happens when year/quarter are omitted (the fallback selection logic), which the schema only tersely states as 'defaults to current quarter.' That is meaningfully beyond the schema text.

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 opens with a specific resource and its payload: 'A BTW (VAT) return: its state, filing deadline and figures.' An agent knows exactly what this returns. It does not explicitly contrast with siblings like query_financials or query_expense_breakdown, so it stops 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?

It clearly explains the no-argument case ('returns the return that needs the user first, as the VAT page does'), which tells an agent when to call it bare vs. with year/quarter. There are no explicit exclusions or named alternative tools, so it is clear context without full when-not guidance.

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