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

Annotations already cover the read-only/idempotent safety profile, and the description adds substantial extra context: 1-3 s runtime, USD pricing per section, the 5/day free quota shared across tools, the caveat that it is heuristic not an audit, and a prompt-injection warning about returned text. That is genuinely useful behavioral disclosure 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 purpose, then input, then returns, then cost/limits — a sensible ordering. It is dense with many short clauses, but virtually every sentence carries information an agent needs.

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 still explains what comes back (DNS records, SPF/DMARC/DKIM/MTA-STS findings with a score out of 8, cert expiry/SANs/key/trust integral). Combined with cost, latency and safety caveats, nothing essential is missing.

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 description largely restates schema facts (253-char limit, no scheme/IP, checks defaulting to all three). The only added nuance is that a single section is cheaper, which is minor. Baseline 3 is appropriate.

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 (inspect) plus resource (domain's DNS, email auth, TLS cert) and scopes it as a single combined call. It is clearly distinguishable from siblings like ip_lookup, rdap_lookup and verify_email, which each cover only one slice.

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 context on when it applies (one-shot domain inspection), the input constraints, typical latency, cost, and the shared free-tier pool with RDAP/email/IP lookups. It does not explicitly say when to prefer a sibling over this tool, but the surrounding context is clear.

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