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

Annotations already declare the safe read-only profile, but the description adds substantial behavioral context beyond that: only Active DNS/DKIM domains are returned, an off-list domainName is rejected at send time with domain_not_available, and an empty list signals that setup was never completed. It also discloses that the account is session-bound and immutable via arguments.

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?

Purpose is front-loaded in the first clause and the ordering is logical (what it returns, then when to call, then the empty case, then the disambiguation note). It is a dense single paragraph, but nearly every sentence adds a distinct operational detail; the sizing is on the long side without being padded.

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?

With no output schema, the description still conveys the return shape (a list of domain strings with an example) and the empty-list semantics. Combined with the send-time constraint and the explicit sibling disambiguation, an agent has everything needed to call this correctly before sending a campaign.

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?

Zero parameters, so the baseline is 4. The description reinforces this by noting it takes no arguments and that the account is bound to the session and cannot be changed via tool arguments, which usefully explains why no scoping parameter exists.

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 verb and resource ('List this account's ACTIVE sending domains'), clarifies what the values are (verified from-domains a campaign can send through), and gives a concrete example. It explicitly distinguishes itself from the similarly named sibling mcp_crm_reports_domain, which searches recipient domains, so an agent can disambiguate without opening either 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?

Gives explicit timing ('Call this before mcp_crm_campaigns_send whenever you need to choose or show the sending domain'), names the alternative it is not (mcp_crm_reports_domain), and prescribes the fallback when the list is empty ('ask the user to complete domain setup rather than guessing'). When-to-use, when-not, and the alternative are all present.

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