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

Annotations already indicate readOnlyHint=false (creates a resource), openWorldHint=true (external WHOIS dependency), and non-idempotent. The description adds context beyond annotations by explaining that WHOIS data is read externallyais and why this monitor is valuable (detecting expiry that uptime checks miss). It also implicitly warns about the WHOIS dependency without contradiction.

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 two sentences, front-loaded with the purpose and a valuable differentiator. Every word contributes: the WHOIS source, the unique failure mode, and the explicit comparison to create_ssl_monitor. No redundant phrases or filler.

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 the tool's moderate complexity (3 params, output schema present, annotations covering read-only/destructive hints), the description covers all essential aspects: purpose, use case, differentiation from a sibling, and external behavior. The output schema handles return values, and the annotations cover safety profile, so the description is complete for agent invocation.

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?

The input schema provides 100% coverage with detailed descriptions for all three parameters (url, name, isActive). The description reinforces the meaning of 'url' by stating it reads WHOIS data, but adds no extra semantics beyond the schema's own descriptions. Since schema coverage is high, a baseline of 3 is appropriate; the description does not enrich parameter understanding further.

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 clearly states the tool's function: watching a domain registration and reporting time until expiry via WHOIS. It uses a specific verb-resource pair ('watch a domain registration') and immediately distinguishes itself from the sibling tool create_ssl_monitor by contrasting registration vs. certificate expiry. This avoids any ambiguity and makes the purpose unmistakable.

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 explicitly tells the agent when to use this tool ('catches the failure no uptime check can see') and provides a clear alternative: 'Distinct from create_ssl_monitor, which watches the certificate rather than the registration'. It also advises that both are worth watching, giving contextual rationale for choosing this over other monitor types.

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