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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is fully covered. The description adds one genuinely useful behavioral fact — that recipient_country triggers an additional treaty-rates dimension of the response — but says nothing about coverage gaps, result shape, or what happens if recipient_country equals the paying country.

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 tight sentences, front-loaded with the core resource and followed by the conditional extension. The trailing ellipsis in the payment-type list is slightly sloppy but costs little.

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 should hint at the return structure (e.g., per-payment-type rate pairs, treaty sub-object). It signals the treaty addition but leaves the overall response shape and the behavior for unsupported countries undocumented, which is a real gap for a lookup tool.

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 75%, and the description still adds meaning: it explains that recipient_country produces treaty maximum rates and enumerates the payment-type families the enum covers. It does not elaborate on the date parameter's 'not_covered' fallback beyond what the schema already states.

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 names a specific resource (withholding tax rates) and scopes it precisely: resident/non-resident by payment type, plus treaty maximum rates when recipient_country is set. It does not, however, distinguish itself from siblings like calculate_withholding_tax or get_tax_treaties, leaving the reader to infer the rates-vs-compute vs rates-vs-treaty split.

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 implied through the payment_type and recipient_country conditions, but there is no explicit instruction on when to call this instead of calculate_withholding_tax (to compute an amount) or get_tax_treaties (to inspect treaty text). No exclusions or prerequisites are stated.

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