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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is covered. The description adds genuinely new behavioral scope: only 'standard' rates are returned (implying reduced/zero rates are excluded), every period is included, and each row carries the enacting law. Ordering and country coverage are not stated.

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 sentence that front-loads the resource and scope, then the returned fields, then the use cases. Nothing is redundant and nothing is padding.

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?

No output schema exists, and the description compensates by naming the returned tuple (from, to, rate) plus the legal basis, which is exactly what an agent needs to interpret results. For a single-parameter read tool this is sufficient; only ordering and jurisdictional coverage are left implicit.

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?

There is a single required parameter with 100% schema description coverage, including the ISO 3166-1 alpha-2 pattern and examples, so the schema carries the full burden. The description adds no meaning beyond 'for a country', which is the baseline for a fully documented parameter.

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 states a specific resource with clear scope: 'Every standard VAT rate period for a country (from, to, rate) with the law that set it.' The word 'history' plus the 'standard' qualifier separates it from the sibling get_vat (current rates), though it never names that sibling 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?

Three use cases are given ('audits, refunds and re-invoicing'), which implies a retrospective-lookup context, but there is no explicit 'use get_vat for current rates instead' routing and no statement of when not to call it. Usage is inferred rather than directed.

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