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

Even though annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, the description adds substantial behavioral context: pricing, non-intrusiveness, free refusal of invalid/private-only domains, scoring behavior for info checks, and MCP/x402 payment behavior. This is highly transparent for a paid external check.

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?

The description is front-loaded with the paid nature and primary use cases, then proceeds to output and payment details. It is information-dense and every major clause is relevant, though the repeated pricing mention and long single paragraph make it slightly less crisp.

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?

For a complex paid domain-security check, the description supplies the key operational context: cost, use cases, refusal behavior, return shape, per-check grading, and MCP authentication/payment requirements. An output schema exists, but the description's summary of return values is still helpful and 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?

Schema coverage is 100%, so both parameters are already documented. The description still adds useful meaning for api_key by explaining the MCP payment flow, x402/MPP being HTTP-only, and what happens without a key, while the domain parameter's format is left to the schema.

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?

The description states a specific resource and scope: a graded domain/email security check covering SPF, DKIM, DMARC, MX, MTA-STS, DNSSEC, CAA, TLS, BIMI, blocklists, and domain age. It also gives concrete use cases (spam diagnosis, campaign preflight, vendor due diligence, Microsoft 365 tenant confirmation), making it clearly distinguishable from narrow sibling tools such as domain_age.

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 gives clear conditions for use: when mail lands in spam, before an email campaign, for vendor due diligence, or to confirm a Microsoft 365 tenant. It does not explicitly state when not to use it or name alternatives, so it earns a 4 rather than a 5.

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