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

With no annotations, the description carries the behavioral transparency burden, and it does well by explaining null-rate handling, non-EU countries being recognized but returning null rates, the absence of HS/NACE mapping, and the no-roll-forward behavior. It does not specify error behavior for unrecognized countries, which remains a small gap.

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 front-loaded with a concise summary, but the second paragraph contains some repetition: the disclaimer about not being a goods classification appears twice, and the motivation example, while illustrative, is somewhat tangential. Still, the remaining detail is relevant and compact.

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 lookup tool with no output schema, the description covers the key behavioral cases: null for missing dates, special handling of non-EU countries, and the no-goods-classification boundary. It does not describe the return shape or error behavior is not fully specified, but for this tool the context is largely complete.

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?

Input schema coverage is 100%, and the description adds meaningful context to both parameters: asOf governs point-in-time lookup with no fall-forward, and country is the EU/recognized-non-EU key. This goes beyond the schema's simple descriptions of ISO dates and country codes.

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 a point-in-time schedule of EU-27 VAT rates (standard, reduced, super-reduced, parking) plus the Union OSS threshold. It explicitly distinguishes itself from a goods classification and from sibling tools like eu_vat_validate by stating that it returns rates, not validation or goods classification.

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 makes it clear this is for looking up dated VAT rate schedules, not for classifying goods, and even explains how it should be used instead of hard-coding rates. It mentions the important limitation that the last known rate is not reused. It could be stronger by explicitly contrasting with eu_vat_validate, but the context is clear.

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