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

Annotations already declare readOnly/openWorld/idempotent semantics, and the description adds genuinely useful context beyond them: the price ($0.0015 USDC on Base, x402) and the payment flow (returns payment requirements unless payment_signature is given). It also reinforces 'no side effects.' It stops short of describing rate limits or the actual verification result shape.

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?

Dense but front-loaded: purpose first, then usage, then price/payment mechanics and a sample link. Sentence count is justified, though the '[Data utilities]' tag and price echo the title.

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 clarify the return contract. It explains the payment-requirements return path well but never describes the actual verification result (deliverability verdict, disposable/MX flags), so an agent can't anticipate the output of a paid, successful call.

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%, so the schema already defines both parameters, giving a baseline of 3. The description adds meaning for payment_signature by explaining the x402 flow and what happens when it is omitted, plus the batching hint lives in the schema itself.

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 (check) and resource (email address) and clarifies the goal (looks real and deliverable), with the title adding the exact checks performed (syntax, MX, disposable, SPF/DMARC). It is unambiguously an email-verification tool, though the description body itself doesn't differentiate it beyond what the title already conveys.

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 usage context: 'before sign-up, outreach or invoicing' and 'Use when you need a quick check with no side effects.' This tells the agent when to reach for it, but there are no explicit exclusions or named alternatives.

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