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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint, so the safety profile is covered. The description adds genuinely non-obvious behavior: the first lookup is a fast partial snapshot while later lookups are fuller, and wait=true blocks for all sources up to ~20 s. This latency/completeness tradeoff is exactly the kind of disclosure annotations cannot carry.

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 dense sentences, front-loaded with the core purpose and sources before the operational notes. Slightly cluttered by the `live`/`subdomains`/`pools` discussion, which reads like mode names but maps to no parameter in the schema.

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-value documentation is not owed. However, the description introduces `live`, `subdomains` and `pools` as if they were selectable outputs without any corresponding schema parameter, which risks the agent attempting an invalid mode argument, and `limit` remains entirely unexplained for a 3-parameter tool.

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 must compensate. It explains wait (blocks for all sources, ~20 s) with real semantic content, but leaves limit completely undefined — an agent cannot tell whether limit caps hosts, names, or sources, nor what the default 100 applies to. Partial compensation only.

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 resource (subdomains of a domain) and the data sources it aggregates (certificate transparency logs, passive DNS, DNS brute force), which is far more informative than the bare name. It does not, however, contrast itself with siblings like dns_records or domain_lookup, and the references to `live`/`pools` modes muddy what the tool's actual output shapes are.

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 implies when to set wait=true ('to wait for every source, up to about 20 s') and hints at a latency/coverage tradeoff, which is useful operational guidance. It gives no explicit when-to-use or when-not-to-use guidance relative to the sibling tools (dns_records, domain_lookup), so tool selection is still left to inference.

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