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

With no annotations provided, the description carries the full burden. It discloses that the tool is paid ($0.02 per call via x402), which is a key behavioral trait. It also clarifies that it 'returns' information, implying no side effects. However, it does not explicitly state whether it is read-only or mention any rate limits or failure modes, but the cost and output transparency add significant value.

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 description is two sentences, with the first sentence densely packing all functional details and the second handling the cost. There is no redundancy or fluff; every word serves a purpose. It is front-loaded with the core functionality, making it easy to scan.

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?

Given that there is no output schema, the description fully enumerates the return values, including place of supply, VAT rate, BT-151, BT-121, bilingual wording, and legal article. It also covers supported standards and input parameters. This makes the tool's behavior and expected results completely clear, leaving no critical gaps.

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?

The schema has zero description coverage, so the description compensates by explaining the meaning of all four parameters: supplier country, customer country, B2B/B2C, and goods/service. It does not specify formats (e.g., ISO country codes), but it provides enough semantic clarity for an agent to map inputs. The mention of 'type' defaulting to 'service' further clarifies its purpose.

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 clearly identifies the tool as an 'EU VAT decision engine' for invoices and e-invoicing, listing specific inputs (supplier country, customer country, B2B/B2C, goods/service) and outputs (place of supply, VAT charge, rate, EN 16931 code, exemption code, wording, legal article). It distinguishes itself from sibling tools like validate_einvoice_eu by focusing on decision-making rather than validation.

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 provides clear context for when to use the tool: when an agent needs to determine VAT obligations for cross-border EU transactions. It implies usage through the listed inputs and outputs, but does not explicitly mention alternatives or exclusion scenarios. This is sufficient for an agent to select it appropriately.

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