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

Despite annotations covering the safety profile, the description adds substantial context beyond them: cost ('included in every plan at no charge'), caching ('a re-check within 90 days reuses the cached verdict'), async execution model, the polling contract, and the semantic meaning of all four verdict states. The explicit 'Never treat catch_all as verified' warning is exactly the kind of behavioral nuance annotations cannot express.

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?

Every clause carries load — cost, caching, execution model, polling instructions, and state semantics — with no redundancy. The async contract is front-loaded before the state definitions, giving a natural reading order.

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 fully compensates by explaining the return value (a job id), the polling path, and the four possible verdict states plus the catch_all caveat. An agent can complete the call and interpret results without any missing information.

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 single parameter's max of 2,000 is already documented in the schema, so the description adds no syntax or format detail beyond it. Per the high-coverage baseline, a 3 is appropriate.

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 — 'SMTP-verify the business emails on saved leads' — and names the provider (MillionVerifier), which cleanly separates it from siblings like enrich_leads or find_contacts. An agent knows exactly what operation this performs 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?

Gives clear operational context: it runs in the background, returns a job id, and must be polled via get_job_status with kind "verify" until completed. It does not, however, state when to prefer this over alternatives such as enrich_leads, so it falls short of full when/when-not routing.

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