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

Annotations only declare readOnlyHint and openWorldHint; the description adds the materially important facts an agent needs before calling — mandatory authentication, the exact rate-limit cost (10 requests of the daily quota), and a paid fallback path with price and chain. It also previews what is returned (score, severity-graded findings, fixes), which is genuine 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?

Two tight sentences: the capability and its return format come first, the auth/cost constraints second. Every clause carries information an agent needs — no restated title, no filler.

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, yet the description states the return contents (numeric score, findings by severity, exact remediation). Combined with disclosed auth, rate-limit cost and payment fallback, an agent has everything needed to decide to call it and to know what comes back.

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, so the schema already documents it fully ('Domain name, e.g. example.com'). The description only implies the parameter via 'of a domain' and adds no syntax or normalization details beyond the schema, so 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?

Names a specific operation (a security audit of a domain) and enumerates exactly what is inspected: DNS, SPF, DMARC, TLS, HTTP headers, WHOIS expiry and IP blacklists. It also states the output shape (0-100 score, findings by severity, exact fixes), which cleanly separates it from the narrower siblings dns_lookup, ssl_check, http_headers and whois.

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 operative context: a paid ipv4.fr API key in the X-Api-Key header, consumption of 10 requests of the daily limit, and an x402 pay-per-call fallback at 0.05 USDC on Base. What it never states is when to choose this over the single-purpose siblings (e.g. a full audit vs. a one-off dns_lookup), so the alternative-selection guidance is only implied by the coverage list.

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