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

Annotations already declare read-only, idempotent, open-world, non-destructive, so the safety profile is covered. The description adds genuinely new operational context beyond annotations: a per-call price of $0.005, a free sample payload, and the shape of the returned data. Rate/pricing disclosure is exactly the kind of extra context that earns credit here.

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-loaded with the purpose, then pricing, then an example and the return shape — dense but zero filler sentences. The inline JSON fragments are slightly harder to scan than prose, but every clause carries information.

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 usefully enumerates the return fields (grade, overallScore, maxPossibleScore, categories[]), which is what an agent needs to decide whether the call answers its question. It stops short of explaining how categories are structured or what the grade scale is, which keeps it from a 5.

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% for the single 'domain' parameter (bare domain name, maxLength 253), so the schema already does the work. The description's example {"domain": "example.com"} reinforces but does not extend the schema's own example. 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 resource and output: a letter grade and point score for a domain's security posture, plus the scored items behind it. This is distinguishable from narrow siblings like domain_tls or domain_dnssec because it is an aggregate posture grade, though the description never names those siblings explicitly.

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?

No when-to-use guidance, no prerequisites, and no routing to or away from alternatives (domain_tls, domain_dnssec, domain_blacklist). The agent must infer from the name alone that this is an aggregate scoring call rather than a component-level check.

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