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

Annotations already declare readOnly, idempotent, non-destructive, open-world, so the safety profile is covered. The description adds genuinely new behavioral context not in the annotations: the $0.005 per-call cost and the full shape of the returned certificate fields, which tells the agent what data it can rely on.

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 a sample request and the return-field list. It is a single dense block rather than cleanly separated sentences, but no sentence is wasted and the most important information comes first.

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 correctly enumerates the returned fields, and the single fully-documented parameter completes the input story. It omits error behavior (invalid domain, no TLS listener, expired cert) and any timeout/latency expectation, which would be useful for a live network check.

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 coverage is 100% and the schema already documents the sole parameter ('A bare domain name, e.g. example.com'). The description's sample call restates that same example without adding format constraints (no-URL, no-IP?) beyond what the schema says, so this is baseline.

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 (the TLS certificate for a domain) and enumerates the exact attributes it covers: validity, issuer, protocol, days until expiry. This is clearly distinguishable from the other domain_* siblings (dns, whois, dnssec, email_auth) without opening any 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?

There is no explicit when-to-use, when-not-to-use, or alternative-tool guidance; an agent must infer from the name that this is the TLS-certificate lookup versus domain_dns or domain_whois. The pricing line and free sample are cost/request mechanics, not usage routing.

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