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

With no annotations, the description carries the full burden and does well: it discloses that the scan is DNS-only, read-only, 'never touches the target,' and that candidate generation is bounded for speed. It does not mention rate limits, resolution timeouts, or how results are ordered, but the safety and performance profile is unusually well covered for an unannotated 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?

One front-loaded sentence with the mechanism and output, followed by two tight clauses covering safety and performance. Every clause earns its place; nothing is redundant with 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?

There is no output schema, so the description must hint at returns — it does ('report which ones actually resolve in DNS'). Safety, scope, and performance are all covered, so an agent has what it needs to call it correctly; only result-shape detail (ordering, fields per lookalike) is absent, which is a minor gap.

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?

Single parameter with 100% schema coverage, so the schema already documents 'domain'. The description implies the parameter is the base domain from which variants are generated but adds no syntax, normalization, or format guidance beyond the schema's own example. Baseline 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?

States a specific compound verb (generate variants + report which resolve) on a named resource (lookalike domain variants), and enumerates the exact variant classes (omission, transposition, homoglyph, adjacent-key, hyphenation, TLD-swap). This clearly separates it from neighbors like related_domains or dns_lookup, so an agent can route to it without opening the schema.

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 phrase 'the registered lookalikes worth checking for phishing or brand abuse' implies the investigative context, so usage is inferable. However, it never states when NOT to use it or names an alternative sibling (e.g., related_domains) for the adjacent question, leaving the agent to infer the boundary.

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