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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), yet the description adds genuinely new behavioral context: price per call ($0.020), a free sample invocation, and — importantly — disclosure of degraded results via the 'inconclusive' verdict and 'not_checked[]' field when checks cannot run. It does not discuss rate limits or latency, but the partial-failure disclosure is the kind of trait annotations cannot express.

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 decision question, then the verdict vocabulary, then pricing/sample, then the return fields — a sensible order with no filler. The inline Returns list is dense but earns its place because no output schema exists; the free-sample snippet is the weakest element but still briefly useful.

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 and a single fully-documented parameter, the description carries the return-value burden and does so thoroughly: verdict enum, 0-100 risk_score, reasons shape, age_days, blocklist listings, unanswered blocklists, https_valid, and not_checked. Pricing and a sample call are also present, so an agent has everything needed to invoke and interpret the result.

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 there is a single parameter, so the schema already documents 'domain' as a bare domain name with maxLength 253. The description's sample payload reinforces the expected shape but adds no syntax or normalization guidance (e.g., scheme, subdomain, trailing dot) beyond what the schema states. 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?

The description frames a concrete decision ('Should an agent click, sign in to, or pay this domain?') and states the resource: a risk score, a three-valued verdict, and plain-English reasons. The composite scope (domain age + blocklists + HTTPS cert) implicitly separates it from single-signal siblings like domain_age, domain_blacklist and domain_tls, but it never explicitly distinguishes itself from the possibly-overlapping domain_security_score, so sibling differentiation is left to inference.

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?

The opening question gives a clear decision context in which this tool is the right call, which is stronger guidance than most definitions offer. It stops short of explicit when-not guidance or naming an alternative tool, so an agent must infer that single-signal siblings are for drilling into individual factors.

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