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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is fully covered without the description. The description adds the conversion direction (HT<->TTC), which is useful, but omits operational details such as rounding behavior or accepted rate constraints beyond what the schema states.

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 short sentences, front-loaded with the primary action, with no filler. The 'Returns:' enumeration is partly redundant against the existing output schema but stays compact and does not harm readability.

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, annotation-backed calculator with a full output schema, the description covers purpose, operation, and return shape adequately, so return values need not be re-explained. The only shortfall is the absence of guidance distinguishing it from sibling VAT tools.

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, rate) are fully documented in the schema, so the baseline of 3 applies. The description restates the HT/TTC concept but adds no new parameter meaning (e.g. how the rate enum interacts with mode) beyond the schema.

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 Belgian VAT') plus the core operation ('convert between HT and TTC'), which cleanly separates it from the many sibling VAT calculators (french/moroccan/swiss/uk/generic). The 'Belgian' qualifier does the jurisdictional disambiguation work, though it never explicitly contrasts the tool with calculate_vat_generic or calculate_vat_reverse.

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 only implied by the HT/TTC conversion framing; there is no explicit when-to-use or when-not-to-use statement and no routing against the neighboring VAT tools. The only pointer ('See list_bundles for related finance-belgique calculators') directs the agent to a bundle rather than clarifying which calculator to pick.

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