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

Adds traits the annotations cannot express: live DNS lookups (openWorld), a $0.50 USDC x402 cost, and the important billing rule that errors are not charged. Annotations only cover the read-only/idempotent safety profile, so the payment and failure-cost behavior here is genuinely additive.

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?

Three tight sentences: what it does and its scoring model first, return contents second, audience and cost last. No filler, and the most decision-relevant information is front-loaded.

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 carries the return-value burden and does so explicitly: per-domain score, grade and issues, plus a summary with grade counts, domains missing DMARC/SPF, and the worst 10. Cost and error behavior are also covered, so nothing material 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?

Only one parameter, and schema description coverage is 100% ('Domains, 1-100'), so the schema already documents the input fully. The description restates the 1-100 cap but adds no syntax, format, or normalization guidance beyond it, matching the baseline 3 for high coverage.

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+resource with explicit scope: 'Score up to 100 domains' email security in one call, and names the exact scoring dimensions and weights. The 'bulk'/'up to 100 domains in one call' framing cleanly separates it from the single-domain siblings like check_domain_email_security and email_security_score.

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 — 'For MSPs and agents checking a client or vendor list' — which tells the agent this is the batch path. It does not, however, explicitly name a single-domain alternative or state when not to use it, so it stops short of the 5 bar.

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