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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: the cost model (free within the daily allowance, then $0.003 USDC per call via x402), which affects whether an agent should call it. It does not clarify whether the output is raw signals or a verdict, but the output schema carries that.

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 sentences, front-loaded with the substantive signal list before the pricing clause. The enumeration is long but each item is a distinct check, so it earns its place; no filler text.

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?

An output schema exists, so return values need not be described, and annotations cover the safety profile. What is present — signals inspected plus cost — is enough to call the tool correctly; the only real gap is routing guidance against sibling URL tools.

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?

There is a single parameter with 100% schema description coverage ('Public http(s) URL'), so the schema does the work and the baseline is 3. The description adds no format, length, or normalization guidance for the url argument beyond what the schema already states.

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 names the resource (a URL) and enumerates the specific safety signals it inspects — redirect chain, TLS cert, domain age, punycode/lookalike tricks, bare IPs, security-header grade — which clearly distinguishes it from generic fetchers like web__read and web__unfurl. It never states the verb explicitly ('check'/'report on'), but the enumerated signals make the operation unambiguous.

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 when-to-use or when-not-to-use guidance, and no sibling is named even though web__read, web__unfurl and domains__facts are obvious alternatives an agent would need to disambiguate against. Usage is only implied by the subject matter.

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