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

Annotations already declare readOnlyHint/idempotentHint/non-destructive, so the safety profile is covered. The description adds the bidirectional net↔gross nature of the operation and the three outputs, but since an output schema exists and 'Returns HT, TTC, and tax amount' restates it, the incremental behavioral value is modest.

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?

Three short sentences, front-loaded with purpose, then usage, then I/O, then a cross-reference. Every sentence carries information and nothing is padded.

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 read-only annotations, a full-coverage input schema, and an output schema, the description supplies what it must (purpose, usage context, a sibling pointer). It would be complete at 5 if it acknowledged rounding/precision or the vat_generic/vat_reverse alternatives.

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%, so the baseline is 3. The description restates the parameters and rate values, but it lists a rate of '0' that the schema enum (2.6/3.8/8.1) does not permit — a small inconsistency rather than added meaning.

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 ('Compute Swiss VAT (TVA/MWST)') and the exact operation ('convert between net (HT) and gross (TTC)'). This clearly distinguishes it from the numerous sibling VAT calculators (calculate_belgian_vat, calculate_french_vat, calculate_uk_vat, calculate_vat_generic) by jurisdiction.

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?

Gives a concrete use context ('invoicing or expense reimbursements in Switzerland') and points to list_bundles for related 'finance-suisse' calculators. However, it never states when to prefer this over calculate_vat_generic or calculate_vat_reverse, so the routing to sibling alternatives is only half-addressed.

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