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

Adds substantial context beyond the annotations: live DNS and registration-date lookups with the rationale ("most phishing domains are days old"), an explicit safety guarantee that the page itself is never fetched, and the full cost model ($0.01 USDC per call after 25 free calls/day) which explains the _payment parameter's role. Read-only nature is consistent with readOnlyHint=true.

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 trigger ("Before opening a link..."), then signals checked, then lookup behavior and rationale, then the safety guarantee, then price. Every clause carries information an agent would otherwise have to infer; no filler.

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 tool that reaches external DNS/registration data with no output schema and a paid path, the description covers cost, safety, and detection scope well. The one gap is that it never indicates what a result looks like (verdict/score/reasons), forcing the agent to call blind on the return shape.

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 explains why expectedBrand matters (brand impersonation detection across 70+ brands, "fails if the domain is not official") and why _payment exists through the free-allowance/pricing disclosure. It stops short of clarifying the format of the returned verdict.

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 (detects/checks) against a specific resource (a link/URL) and enumerates the exact classes of signal examined: homoglyphs, typosquats, brand impersonation, user@host hidden destinations, unsafe schemes, risky TLDs. The resource is plainly distinct from the siblings (address_check, payment_check), so an agent can disambiguate 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?

"Before opening a link or entering credentials" gives an explicit trigger condition, which is the strongest form of usage guidance. It doesn't state when-not-to-use or name a sibling, but the sibling set covers wholly different resource types (addresses, payments), so the omission costs little.

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