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

Annotations already declare readOnly/idempotent/non-destructive; the description adds real behavioral context beyond that — an external VIES lookup occurs, reverse charge applies only on a valid VAT ID, and the result is explicitly non-binding. It does not mention latency/fallback behavior when VIES is unavailable.

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?

One dense sentence with the key qualifier (non-binding) placed at the end as a caveat, and the priced scope front-loaded. The parenthetical and semicolon make it slightly run-on, but every clause adds information.

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 6-param calculation tool with no output schema, the description omits what the response contains (amount, currency, VAT rate, line items) and says nothing about `zip` or plan validity. Adequate to call correctly, but not complete for interpreting the result.

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?

With 50% schema coverage, the description compensates well: it clarifies period as monthly/annual, addon as an optional dpa package, vat_id as driving reverse charge, and country as the billing country. The `zip` parameter and the plan's example values are left unexplained in the description.

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+resource and narrows scope precisely: exact price of a *new* subscription, VAT-inclusive for the billing country. That implicitly separates it from create_quote and request_enterprise_quote (non-binding vs. binding), though no sibling is named explicitly.

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?

Usage is implied rather than stated: 'non-binding' and 'exact price' hint that this is a pre-quote estimate, not an order or a formal quote. There is no explicit when-to-use/when-not statement or named alternative (e.g. use recommend_plan first, use create_quote to commit).

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