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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered and the description does not contradict it. The description does add value by disclosing what the answer contains (the need/no-need rules, the $299 service, IRS processing time), which reveals a promotional component an agent should be aware of. It does not say whether the response is a verdict or prose, nor how the second parameter changes the answer.

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 sentences, front-loaded with the core question and then the required/not-required split, with no wasted preamble. The trailing sentence about the paid service and IRS processing time is slightly promotional but is legitimately part of what the tool returns.

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?

This is a read-only informational tool with no output schema, so the description must convey what comes back — and it does, naming the rules covered, the service offering, and processing-time content. Missing only a note on answer shape and on whether has_ssn_or_itin changes the response, which is a minor gap for a two-parameter advisory 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 description coverage is 100% and the enum values are self-explanatory, so the schema carries the parameter burden. The description does not mention any parameter, does not explain how 'situation' maps to the enumerated triggers, and does not say whether has_ssn_or_itin short-circuits the answer at all. Baseline 3 applies.

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 states a specific function: it explains when an ITIN is required and when it is not, and it lists the concrete triggers (tax return, US-source income, treaty benefits, bank/marketplace requests) plus the explicit non-trigger (LLC formation, EIN). The scope is clear, though it never names a sibling tool to contrast with, so the differentiation from tax_filing_estimate or ein_timeline is left implicit.

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 by the framing question ('Does a non-resident founder need an ITIN?'), and the enumerated situations suggest when the answer is relevant. But there is no explicit statement of when to call this tool versus the siblings, no mention of prerequisites, and no note on what to do with the answer.

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