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

Annotations already declare readOnlyHint=true, openWorldHint=false, idempotentHint=true and destructiveHint=false, so safety is covered. The description adds real behavioral context beyond that: it is format-only with no government lookup, and it warns against submitting real identifiers, which is privacy context annotations cannot convey.

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?

Four short clauses, all front-loaded around the scope and safety constraint. 'Do not submit real identifiers' and 'synthetic ... fixtures' partially overlap, a minor redundancy in an otherwise tight description.

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 single-param read-only validator with no output schema, the description covers scope, safety, and the key limitation (no government lookup, no identity confirmation). It does not say the tool returns a boolean/pass-fail result, a minor gap given no output schema exists to state it.

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% and the single param is fully documented in the schema. The description adds a little by naming EIN/SSN/ITIN as accepted families, but does not describe expected input format or lengths beyond the schema's maxLength, so 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 verb and resource — format-only checks on US EIN/SSN/ITIN identifiers — and names the exact identifier families accepted. An agent can distinguish it from sibling validators like is-ssn-safe or is-vat-safe without opening the schema.

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?

It gives explicit when-to-use (only with synthetic EIN/SSN/ITIN fixtures) and when-not-to-use (do not confirm identity or IRS registration), which is exactly the routing guidance an agent needs. The scope limit is unambiguous.

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