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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered. The description usefully clarifies that the return is a 'rule' rather than a computed date, but says nothing about what happens for unsupported countries or what the rule contains.

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?

A single sentence with the primary lookup front-loaded and the optional qualifier trailing. No filler, nothing redundant.

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 two-parameter read-only lookup with fully described parameters and complete annotations, the definition is nearly sufficient. It stops short of saying whether a missing/unsupported country yields null or an error, which is the one operational detail an agent would still want.

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 coverage is 100%, so both parameters are already documented with ISO alpha-2 format and role. The description's 'source country' and 'residence (treaty partner) country ... for treaty exceptions' largely restate the schema's own wording, adding only mild framing.

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?

Specific verb ('Get') plus a precisely scoped resource ('withholding-tax reclaim deadline rule'), qualified by source country and optional treaty partner. None of the siblings (estimate_dividends, estimate_refund, list_countries) return a deadline rule, so the resource alone disambiguates it.

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?

The word 'optionally' signals when the treaty_partner argument applies, but there is no explicit when-to-use guidance, no stated precondition (e.g. only call after identifying the source country), and no mention of alternatives. Usage is implied rather than instructed.

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