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

With no annotations, the description carries the full burden, and it delivers unusually useful operational detail: the tool costs $0.001 USDC per call via x402, so the agent knows a payment/auth step is required before invoking. It also discloses the checks performed and the 0-100 score range. It stops short of covering failure modes, rate limits, or whether results are cached.

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 sentences, zero filler. The verification scope is front-loaded and the cost constraint is appended as a distinct, actionable fact.

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?

No output schema exists, so the description carries some return-value burden, which it partly meets by naming the quality score 0-100 and the check categories. The payment model is also covered. It could say more about the exact response fields, but for a one-parameter read tool this is close to complete.

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?

There is a single parameter and schema description coverage is 100%, so the schema already documents 'email' fully. The description adds no format or validation nuance beyond that (e.g., whether aliases or international addresses are accepted). Baseline 3 is appropriate when the schema does the work.

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 (verify) and resource (email address), then enumerates exactly what is checked: syntax, MX records, disposable-domain and role-address detection, plus a 0-100 quality score. The lone sibling, 'health', is a completely different concern, so differentiation is trivially satisfied and an agent can route correctly 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?

The description makes the use case self-evident (validate an email before sending), but never states when to call it versus not calling it, nor any prerequisites. With only one unrelated sibling there is little routing ambiguity, so implied usage is adequate rather than deficient.

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