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

With no annotations, the description carries the full burden and does well: it discloses that lookups are live, that no API key is required, the rate limit (5 free calls/day across all tools), and the cost model (0.01 USDC per call via a prepaid balance). It does not cover latency, failure behavior, or caching, but the auth and rate-limit context is exactly the kind of thing annotations would normally provide.

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?

Opens with a front-loaded framing question, then the capability list, then the use case, then operational constraints — a logical order. The capability enumeration is long but each item is a distinct return value the agent would want to know, so it earns its space.

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?

No output schema exists, so the description must describe returns — and it does, listing the concrete categories of findings. Combined with the auth/cost constraints, an agent has everything needed to call this correctly.

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%, so the baseline is 3. The description does add billing meaning for `key` ('pass `key` to use a prepaid balance (0.01 USDC per call)') beyond the schema's 'Optional API key from create_key'. `domain` is only implied, but the schema already documents it as a public hostname.

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 (check/vet) and resource (domain) and enumerates exactly what it returns: RDAP registration age and registrar, DNS, SPF/DMARC, TLS certificate health, redirect chain, security headers, and plain-language findings. This aggregates and clearly exceeds the narrower siblings (domain_registration, email_auth, tls_certificate), so an agent can distinguish it without opening the schema.

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 a concrete use case: 'vet a merchant, sender or link before trusting it.' That is clear context for selection. It does not, however, name the narrower alternatives (domain_registration, email_auth, tls_certificate) or state when to prefer them, so there is no explicit exclusion guidance.

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