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

Annotations already cover the safety profile (readOnly, idempotent, openWorld), so the bar is lower, and the description still adds meaningful behavior: multiple source backends, incremental result richness across repeated calls, and an explicit ~20s upper bound on wait. This is useful operational context beyond the annotations.

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 sentences, front-loaded with the resource and sources before the behavioral detail. However, the `live`/`subdomains`/`pools` clause consumes a full sentence without a corresponding parameter or observable to anchor it, so it does not fully 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?

An output schema exists so return values need not be documented, and the wait behavior is covered. But the description references `live`/`subdomains`/`pools` modes with no matching input parameter, and leaves `limit` undefined, so an agent cannot fully resolve how to select a mode or bound results.

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%, so the description carries the burden. It explains `wait` well (blocks for all sources, up to ~20s), but `limit` (default 100) is never explained — limit of what is left to inference — and `domain` gets no format guidance.

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+resource (subdomain enumeration of a domain) and names its data sources (certificate transparency logs, passive DNS, DNS brute force), which clearly separates it from siblings like dns_records and domain_lookup. The dangling `live`/`subdomains`/`pools` tokens muddy it slightly, since none correspond to a visible parameter.

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?

It gives real usage context: first lookup returns a fast snapshot, later lookups are fuller, and `wait=true` waits for every source up to ~20s — enough for an agent to decide on a call strategy. It does not, however, state when to prefer this over the sibling tools.

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