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

readOnlyHint=true already tells the agent this is a safe read, so the description only needs to add context. It adds the GET endpoint path, which corroborates read-only behavior but is largely redundant; it says nothing about pagination, result volume, or whether taxes are merchant-scoped vs global beyond the phrase "set up for the merchant".

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 purpose, with the endpoint as secondary detail. Nothing wasted and nothing buried.

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 zero-parameter, read-only list tool this is close to sufficient. The only gap is that with no output schema, the description doesn't hint at what the returned tax-rate objects contain or whether the list is paginated — a small omission given the tool's simplicity.

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 the baseline is 4. The description correctly implies no filtering or pagination inputs are required, consistent with the empty 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 ("List the tax rates set up for the merchant"), which is unambiguous and clearly distinct from the other list_* siblings by resource. The API endpoint reinforces the resource mapping. It stops just short of a 5 because it does no explicit sibling routing, though none is really needed here.

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 — an agent can infer it should call this when it needs merchant tax rates, but there is no stated when/when-not, no prerequisites, and no mention of alternatives (e.g., fetching a single tax rate). Minimum viable guidance.

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