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

Annotations already cover readOnlyHint=true, idempotentHint=true, and openWorldHint=false. The description adds behavioral detail by noting that input can be a domain or any URL, and that the human verdict may not exist ('where one exists'). This goes beyond the structured annotations without contradicting them.

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 with no filler. The core action is front-loaded, followed by a compact attribute list and a practical use case, making every sentence earn its place.

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?

Given a single well-documented parameter, an output schema, and annotations covering safety and idempotency, the description provides all needed context: what data is returned, how to identify the directory, and why to use the tool. Nothing critical 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 domain parameter's description is fully self-explanatory with examples. The description repeats 'by domain or URL' but adds no new semantic information beyond what the schema already provides, so the baseline 3 applies.

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 states a specific verb and resource ('Look up one directory') and enumerates the exact data returned (Ahrefs DR, dofollow/nofollow, price, badge swap, submit URL, human verdict). This clearly differentiates it from siblings like find_launch_directories (plural) and recommend_launch_directories by emphasizing singular lookup and the vetting use case.

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 usage context: 'Use it to vet a directory before paying for a listing.' This tells the agent when to invoke it, but it does not name alternatives or state when not to use it, so it misses the full exclusion guidance required for a 5.

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