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

Annotations only cover safety/open-world hints; the description adds substantial context beyond them: paid x402 pricing tiers, the two-call PaymentRequired handshake with _meta["x402/payment"], free cached repeats within an hour, and the honest caveat that 'unknown stays unknown' and a paid scan is not a guarantee. That is exactly the operational behavior an agent needs before invoking a paid tool.

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 safety question and the cost warning before the mechanics, and the quick-vs-full contrast is easy to scan. It is dense but mostly load-bearing; the pricing is stated twice (title and first sentence), a minor redundancy.

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?

Return values are declared by the output schema, and the description still summarizes the verdict/score/action shape so an agent knows what to expect. Combined with full parameter coverage, a documented payment flow, and caching semantics, nothing an agent needs to call this correctly 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%, so baseline is 3, but the description adds real meaning: it specifies what each tier actually performs (reputation/lookalike/cached vs. live intel, DNS/SSL, impersonation, wallet extraction, redirects) rather than just restating cost. The identity of the payment field is not explicitly described.

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 and resource — check whether a URL is a phishing/typosquat/scam link — and frames the outcome (safe to click). The title and first sentence make it unmistakably distinct from sibling payment/utility tools like x402_check or usdc_balances.

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 when-to-use context ('before you click it') and explicit tier selection guidance: quick:true (default) for reputation/lookalike/cached intel, quick:false for live threat feeds, DNS/SSL, redirects. It also prescribes the payment handshake sequence. It does not name a sibling alternative or state when not to use it, so it stops short of a 5.

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