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

Annotations already declare readOnlyHint=true, so the safety profile is covered, but the description adds real context beyond them: it discloses the V1 auth constraint (works without a V3 token) and names the underlying endpoint (GET /tax). It says nothing about rate limits or latency, but for a static config lookup that is minor.

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, all front-loaded: what it returns, how to use the results, and the auth caveat plus endpoint. No filler, and the endpoint reference is compactly placed at the end.

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 and no parameters, the description carries the load well by naming the returned fields (name and percentage) and the auth requirement. The only loose end is that the overlap with the sibling smartbill_list_vat_rates is left for the agent to resolve from the '(V1)' title and the V3-token note.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The extra sentence about tax_name/tax_percentage describes how the returned values are consumed elsewhere, which is useful but belongs to usage rather than parameter semantics.

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 (list the VAT rates configured in the account) plus the returned fields (name and percentage), which is far more than the title alone. However, it never names the near-duplicate sibling smartbill_list_vat_rates, so the agent must infer from 'V1'/'Works without a V3 token' which of the two VAT-listing tools to pick.

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 clear context for when this tool is the right one ('Works without a V3 token'), which implicitly routes the agent here when no V3 token exists, and even explains downstream usage of the results (name as tax_name, percentage as tax_percentage on document lines). It stops short of explicitly naming the alternative to use when a V3 token is available.

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