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

Annotations already declare readOnly/idempotent/non-destructive, yet the description still adds non-obvious behavior: nothing is created and no email is sent, the domain is entered on the dashboard after sign-in, and monitoring only begins once ownership is proven with a DNS record. It also tells the agent to render signup_url as a link alongside the message, which is a presentation requirement no structured field captures.

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 when-to-use condition and the exclusion are front-loaded and every clause carries information. The opening sentence is long and heavily enumerated, with an explanatory parenthetical about five locations/four continents that is nice color but weighs down the entry point.

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 and the description still orients the agent to its two fields; safety is covered by annotations and reinforced by the no-write/no-email statement. The full lifecycle (signup link → dashboard entry → DNS proof → monitoring active) is spelled out, leaving no ambiguity about what happens after the call.

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 coverage is 100% and the single domain parameter already documents format, subdomain support, and punycode normalization, so the baseline applies. The description adds only the ownership precondition ('a domain they own'), not any format or syntax detail beyond the schema.

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 second sentence states precisely what the call returns (signup_url plus a short message) and what it does not do (create anything, send email), so the agent knows this is a link hand-off, not a setup action. It separates itself from diagnostic siblings via 'not for a one-off question about whether a site is down right now', but it never contrasts with the very close sibling add_monitored_domain, which is the one real source of selection confusion.

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 a concrete, enumerated trigger list (DMARC/RUA monitoring, new-sender monitoring, auth alerts, DNS and uptime-down alerts) and an explicit exclusion for one-off 'is it down now' checks. What's missing is naming the actual alternative tool for that excluded case, so the agent must infer it from the sibling list.

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