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

Annotations only declare readOnlyHint and openWorldHint; the description adds real behavioral context beyond them — that it performs live DNS resolution, RDAP lookups and follows the full redirect chain, and that each call costs $0.01 USDC on Base via x402. The cost and network-lookup disclosure are exactly what an agent needs before invoking it. It does not say whether page content is fetched or whether the URL is disclosed to third parties, so a 4 rather than 5.

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?

Purpose is front-loaded in the opening clause, followed by the check list, the return values and the price — a sensible order with little wasted text. The middle clause is a dense, comma-stuffed list, which is efficient but requires the agent to parse one long sentence for the differentiating details.

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?

For a one-parameter tool with no output schema, the description covers what an agent needs: scope of checks, that it returns a verdict plus a 0-100 risk score and flags, plus the per-call cost. The only gap is interpretation guidance for the risk score (thresholds or what 'flagged' implies for proceeding), which a caller must infer.

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 ('the URL to check (http/https)'), so the schema already carries parameter meaning. The description adds no input guidance beyond implying the same http/https scope and that all listed checks run against that one URL. 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?

Names a specific verb and resource ('Link / URL phishing pre-check') and then enumerates exactly what is checked: brand look-alikes, punycode/mixed-script hosts, credentials-in-URL, high-abuse TLDs, RDAP domain age, DNS resolution and the redirect chain. That enumeration makes it distinguishable from siblings like web_security_headers, domain_whois and web_brand 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?

Explicit about when to use it: 'before an agent opens, clicks or forwards a link', which is a concrete decision point. It stops short of naming alternatives (e.g. domain_whois for registration history, web_security_headers for header posture) or stating when this check is unnecessary, so it is clear but not fully routing.

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