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

Annotations already cover the read-only/destructive profile, and the description adds substantive behavior beyond them: the tool returns `confidence` and `note` that must be relayed verbatim, local/city taxes are excluded, and the merchant decides the final rate. That is exactly the extra context an agent needs.

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?

Front-loads the purpose and the not-a-mutation warning, then layers examples and output-handling instructions. Every sentence earns its place, though the output-handling clause is somewhat dense in a single sentence.

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 no output schema, the description compensates by explaining the `confidence` and `note` return fields and the exclusion of local taxes — the two things an agent would otherwise get wrong. Nothing needed to call it correctly is missing.

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 already documents both `country` and `state` including the 'needed for US and CA' caveat, so the schema carries the parameter burden. The description's mention of country/state/province adds no syntax beyond what the schema provides.

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 ('look up') and resource ('statutory headline rate for a country / US state / Canadian province'), and explicitly distinguishes itself from hub_create_tax_rate. The example phrasings ('what should I charge in Ontario') make the scope unambiguous.

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?

Explicitly states when to use it and when not to: 'this is a reference lookup — it changes NOTHING and creates nothing; use create_tax_rate to actually charge it.' Names the alternative tool and the condition that selects it.

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