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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, covering safety and mutation. The description adds valuable context beyond annotations: it states it cannot spend money (a cost constraint) and lists the specific return fields (registered, resolves, serves, parked, classification, liveness). This enriches the behavioral picture without contradicting any annotation.

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 exactly two sentences: the first front-loads the core action and constraint, the second provides the alternative tool and the return summary. Every word earns its place, with no fluff or repetition.

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 parameter, no output schema, and moderate complexity, the description is fully sufficient. It explains what the tool does, its constraints, its alternative, and the shape of its return data. An agent has everything needed to invoke it correctly without further elaboration.

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 description coverage is 100% for the single 'candidates' parameter, which already explains it expects full domain names with a max of 25. The tool description adds the notion of an 'explicit list', implying exact matches rather than fuzzy or conceptual input. This is a subtle nuance beyond the schema but not substantial—the schema already carries the core meaning, so a baseline score of 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?

The description explicitly states the verb 'Classify' and the resource 'an explicit list of candidate domains' with a clear maximum of 25. It also distinguishes itself from suggest_names, which is a sibling tool, making the purpose unambiguous and easy to differentiate.

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 explicitly says to use suggest_names instead when you have a concept rather than a list, giving clear when-to-use and when-not-to-use guidance. It also notes that the tool is read-only and cannot spend money, which further clarifies appropriate usage.

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