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

Annotations only cover the safety envelope (readOnly, idempotent, openWorld). The description goes well beyond them: up to ten resolving names returned, same_infra interpretation, unknown-vs-free semantics, complete=false while any name is unknown, unregistered names omitted, and the critical 'never a verdict / never call one malicious' constraint. This is exactly the behavioral context an agent cannot derive from structured fields.

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?

Front-loads the trigger condition, then packs behavioral rules into dense, information-bearing sentences ('resolving only means the name is registered', 'unknown, never as free'). It is long, but nearly every clause prevents a concrete misuse, so little is wasted.

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?

For a read-only, output-schema-backed lookup, the description supplies everything needed to call and interpret it correctly: scope, trigger, the safety/'never a verdict' caveat, and the escalation path to start_monitoring_signup. Nothing material is missing.

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?

Only one parameter, documented at 100% schema coverage including bare names, subdomains, punycode normalization and what does not belong. The description adds only the general 'DNS-only' framing, not parameter-specific detail, so the 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 precise verb+resource ('checks the closest variants of the name') and immediately scopes it as DNS-only, so an agent can distinguish it from get_lookalikes and DNS-record siblings. The opening usage clause names the exact user intents (lookalike, typosquat, impersonation) that select this tool.

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?

Explicitly states when to use it ('when the user asks about lookalike, look-alike, typosquat or impersonation domains') and names start_monitoring_signup as the alternative for recurring checks. It does not, however, clarify the boundary versus the similarly named get_lookalikes sibling, so the routing is not fully unambiguous.

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