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

With no annotations, the description must carry the behavioral load. It discloses that discovery is 'passive' (a useful trait), but omits any details about data sources, rate limits, output format, or whether it requires authentication — far too little for a discovery tool.

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 extremely concise (two words) and front-loads the core purpose. However, its brevity leaves critical gaps for a tool with no annotations or schema descriptions, making it under-specified rather than optimally concise.

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 simple tool with one required parameter, no annotations, and no output schema, the description should at least explain the parameter's role and expected output. It provides only the purpose, leaving the agent without enough context to invoke or interpret results confidently.

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 0% and the single parameter ('domain') has an empty description. The tool description does not mention the parameter at all, adding no meaning beyond the schema's bare name and type.

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 'Passive subdomain discovery' clearly states a specific verb (discovery) and resource (subdomains), distinguishing it from siblings like dns_lookup or whois_lookup. It does not, however, explicitly name alternatives or scope, so it stops short of a 5.

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?

There is no guidance on when to use this tool versus alternatives (e.g., dns_lookup, security_scan), no prerequisites, and no exclusions. The description only implies usage from its purpose, providing no actionable context.

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