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

Goes well past the annotations: it discloses the 127.0.0.x return encoding, an explicit false-negative caveat ('not listed means not in current lists, not that the domain is safe'), and the payment model ($0.002 USDC per successful call via x402, failed calls free). For a paid external lookup, that pricing and result-interpretation detail is exactly the context an agent needs.

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?

Three tight sentences: purpose first, result interpretation second, cost third. Nothing is redundant and no sentence could be dropped without losing information.

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 an output schema present and only one parameter, the description covers the remaining burdens — return-code meaning, false-negative risk, and per-call billing — leaving no significant gap for correct invocation.

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 the single parameter is documented in the schema as a domain such as example.com. The description adds no further parameter-level detail (no subdomain handling, IDN, or URL-vs-domain distinction), so 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?

States a specific verb (checks) and a specific resource (a domain) against a named source (SURBL multi.surbl.org spam/phishing URI lists). Among the many reputation siblings, the explicit naming of SURBL as the data source makes this tool immediately identifiable.

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?

Usage context is implied rather than stated: it is clearly a spam/phishing URI reputation check, but it never says when to prefer it over near-identical siblings like security_spamhaus_zen or security_spameatingmonkey, nor any exclusion criteria. The false-negative caveat guides interpretation of results but not tool selection.

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