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

Annotations already indicate read-only, non-destructive, idempotent behavior. The description adds valuable transitive details: keyless operation, 1-hour cache TTL, sub-10-second p95 SLA, and the generation of a 0-100 reputation score with P0/P1/P2 signal tiers. These specifics go beyond annotations and help set expectations.

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 dense yet well-organized: it starts with the core purpose, then lists checks, then discusses input flexibility and signal levels, and finally operational constraints. Every sentence carries distinct information, and the length is appropriate for the tool's complexity.

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 tool's complexity and the presence of an output schema (which explains return values), the description is complete: it covers inputs, specific checks, output signals, performance characteristics, and constraints. No crucial usage aspect is missing.

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 descriptions cover all parameters (domain, email, checks, async) at 100%. The description augments the 'checks' parameter by explaining the meaning of check types via P0/P1/P2 signal examples, and also clarifies the dual input format (domain or email). This adds value beyond the schema but does not fully explain every nuance (e.g., async semantics are only in 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 clearly identifies the tool as a comprehensive email domain health check, enumerating specific checks (MX, SPF, DKIM, DMARC, DNSBL, TLS, WHOIS) and deliverability signals. This specific verb+resource combination distinguishes it from sibling tools like 'domain_tech_fingerprint' which focus on different aspects.

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 provides clear context for when to use the tool: for email deliverability assessment via domain/email input. It mentions keyless operation and SLA, implying readiness for production use. However, it does not explicitly compare to alternative tools or state exclusions, so it falls short of a 5.

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