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

Adds substantial context annotations do not carry: 3 free calls/day across all tools, then $0.0025 USDC via x402 or card credits, with the in-band payment parameter path (params._meta["x402/payment"]) disclosed. It also discloses the no-DNS/fastest trait. Minor tension: openWorldHint=true sits alongside an 'offline, no DNS' claim that is left unexplained, which slightly muddies the external-contact picture.

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?

Front-loads the pricing/quota constraint, then the capability, then the when-to-use routing; all sentences earn their place. Slightly dense and repeats the 'quick' framing across the purpose and usage sentences, but no filler.

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?

Given an output schema exists, the description needn't explain return values, and it covers quota, payment, capability scope, and alternatives. The one loose end is the unexamined relationship between the 'offline' behavior and openWorldHint=true, which leaves the agent guessing about external data sources.

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% for the single 'email' parameter, so the schema already does the work. The description only implies single-address scope through "for one email", adding no syntax, normalization, or validation details beyond the schema. 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?

States a specific resource and the exact checks performed: offline syntax check, ~9,900-domain disposable list, role address and free-mail flags, explicitly "no DNS". It names and contrasts the two sibling tools (email_verify adds MX, email_verify_batch for lists), so an agent can pick it without opening a 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?

Has an explicit "When to use" clause plus a direct alternative: "Use email-verify for MX checks" and "email-verify-batch for lists". The condition that selects each sibling is spelled out rather than inferred.

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