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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false) and openWorldHint=false, so the agent knows this is a pure local computation. The description confirms it supports all 4 rates and enumerates the return fields, but that return shape is largely redundant with the output schema, so it adds limited behavioral context beyond structured data.

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?

Two tight sentences, front-loaded with the primary purpose followed by a secondary navigation hint. Minor waste in restating the return fields already present in the output schema.

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 a full schema, an output schema, and complete annotations, the agent has everything needed to invoke correctly; the description's contribution is the jurisdiction scoping and conversion framing. Nothing critical is missing, though a rounding/locale note would be the one thing a French VAT tool might usefully add.

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 description coverage is 100%, and both enums (mode: ht/ttc, rate: 2.1/5.5/10/20) are already documented in the schema. The description restates HT/TTC and the rate coverage but adds no syntax, rounding, or edge-case detail, so baseline 3 is correct.

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 and resource ('Calculate French VAT (TVA)') and immediately names the two conversion directions (HT/TTC). It is clearly distinguishable from the many sibling VAT calculators (Belgian, Swiss, Moroccan, generic, reverse) by naming the French jurisdiction 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?

The HT/TTC conversion framing implies when the tool applies, but there is no explicit when-to-use versus the obvious alternatives (calculate_vat_generic, calculate_vat_reverse, calculate_belgian_vat). The only routing hint is a pointer to list_bundles for related 'finance-france' calculators, which is a discovery aid rather than usage guidance.

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