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

Annotations already cover read-only/idempotent/open-world safety, so the bar is lower. The description still adds substantial value: partial=true handling of unavailable categories, 3-10 s latency, x402 pricing ($0.03 USDC in _meta["x402/payment"]), and that errors are not charged. That is rich behavioral context beyond the annotations.

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 core purpose and verdict framing, then layers in categories, return shape, alternatives, and payment semantics. Every clause earns its place, though the single dense paragraph is longer than strictly needed for a one-parameter tool.

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 picks up the slack by describing exactly what comes back: one letter, a 0-100 score, per-category points, and top fixes. Combined with cost, latency, and partial-result semantics, an agent has everything needed to call and interpret it.

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% and there is only one parameter, so the schema fully documents the accepted hostname/URL format. The description adds no syntax or format detail beyond that, 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 a specific verb and resource (grade a domain's security posture A-F) plus the scope of work it performs (TLS, DNS/DNSSEC/CAA, registration, email-auth, HTTP headers). It also distinguishes itself from siblings by positioning as the verdict tool rather than the raw-data checks.

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?

Explicitly says to use it when you want a verdict, and names alternatives (site_health and the single checks) for raw data. Also names the target scenarios (vendor-risk or due-diligence), leaving little to inference.

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