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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds the cost ($0.01) and the underlying route (GET /x402/email-check?q=), which is useful context, but it omits the notable behavior that a first call without payment returns a live 402 challenge — that is only explained inside the payment parameter description.

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 short sentences, front-loaded with what is checked and followed by cost/route. Nothing is padded, though 'outreach verdict' is left unexplained and costs a small amount of clarity for the terseness.

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 the paid x402 flow and absence of an output schema, the description leaves out the two behaviors an agent most needs up front: that an unpaid call returns a 402 challenge, and what the 'outreach verdict' actually contains. The schema compensates for the payment mechanics, but the top-level context is thin for a paid, multi-check tool.

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%; both q and payment are fully documented in the schema, including the x402 settlement flow. The description only reiterates that q accepts a domain or address, adding essentially no meaning beyond the schema, so the 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 the exact record types returned (MX, SPF, DMARC) plus an 'outreach verdict' for a domain or address, which is specific enough to separate it from the security/polymarket/weather siblings. The verb is only implied by the tool name rather than written into the description, so it falls just short of a 5.

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 names no alternatives and gives no conditions for choosing this tool over siblings like check_security_headers or check_webmcp. The use case is inferable from the purpose statement, but no explicit when-to-use or when-not-to-use guidance is provided.

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