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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely useful behavioral context: which blacklists are queried, the count (24 IP lists), the no-DNS-resolution behavior, and that results are per-list listing status.

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 tightly packed sentences with zero filler; the resource scope and input-mode distinction are front-loaded before the return behavior.

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 single-param, read-only lookup with no output schema, the description covers what is queried, how the target is interpreted, and the shape of the result. Nothing an agent needs to invoke it 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% and the single param is well documented, so baseline is 3. The description adds meaning beyond the schema by specifying what each target type is checked against and clarifying that no resolution occurs, which affects how the agent should supply the value.

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 (check) and resource (domain/IP against blacklists), and explicitly distinguishes the two input modes with named example lists. An agent can immediately tell this is a blacklist lookup, distinct from siblings like whois_lookup or check_spoofability.

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 context on how the target is interpreted ('Checks the exact target given: domains are not resolved to IPs'), which is a real usage constraint. However, it offers no explicit when-to-use vs. alternatives guidance relative to sibling tools such as check_spoofability.

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