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

With no annotations, the description carries the full burden. It discloses a key behavioral trait: lists refusing public queries are reported as 'unavailable' rather than falsely clean, and warns to read total_checked alongside listed_count. This is valuable transparency beyond a basic flag check.

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?

The description is two sentences, front-loaded with the action and scope, then providing usage guidance and a critical caveat. No redundancy or 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 single-parameter tool with no output schema, the description provides adequate context: the use case, the blacklist count, the breakdown format, and a caution about interpreting results. It could further clarify the exact output structure, but the essentials are covered.

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% for the single 'ip' parameter, with a clear description and pattern. The tool description adds the context that DNSBLs are IPv4-only and the purpose, but this mostly reinforces the schema without adding new semantic detail.

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?

The description uses a specific verb ('Check') and resource ('IPv4 address against 12 major spam and abuse blacklists'), listing example blacklists and the per-list breakdown. This clearly distinguishes it from sibling tools like ip_lookup or vpn_proxy_check.

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?

The description gives an explicit use case: 'Run this before sending bulk email from a new IP, or when mail is being rejected.' This provides clear context for when to use the tool, though it does not mention alternatives or when not to use it.

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