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

Annotations already flag destructiveHint=true and openWorldHint=true, but the description adds several traits annotations do not carry: it never edits DNS itself, plan limits apply (maxSendingDomains), owner-only auth is enforced, status auto-refreshes every two minutes, remove unassigns the domain from events, and requestId reuse rules are spelled out. The retry semantics also reconcile the non-idempotent annotation rather than contradicting it (a retry with the same requestId is safe, a new change needs a new requestId).

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 and the add/verify workflow are front-loaded, and nearly every clause earns its place (permissions, plan limits, refresh interval, guide pointer). It is a dense single block of parenthetical asides, however, which makes the four-action structure harder to scan than a short per-action list would be.

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 four-action mutation tool with a generic payload object and no output schema, the description supplies what is needed: what gets created and returned (dnsRecords, detectedProvider, domainId), what verify returns (status, pendingRecords, isDefault, senderIdentity), what remove does to downstream assignments, the auth constraint, and a link to the MCP workflow resource.

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 payload schema is effectively opaque (free-form object, additionalProperties {}), so the description must carry the burden, and it does: it maps each action to its fields (add: domain + requestId; verify/setDefault/remove: domainId + requestId). It leaves unaddressed the schema-mentioned extras (expectedRevision, cursor, reviewHash) and never explicitly says these fields live inside payload, so it is strong but not exhaustive.

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 names a specific verb and resource ('Owner-confirmed connection of the organizer's own email sending domain') and enumerates the four distinct operations (add, verify, setDefault, remove) with what each does. It also distinguishes itself from adjacent tools by naming list_custom_domains (read-only status) and set_email_sender_identity (identity revision), so an agent can route correctly 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?

It states when a verified domain is required ('Email invitations, campaigns, click measurement and A/B tests all require a verified one') and prescribes the workflow: add -> create every record at the DNS provider -> verify. It explicitly states the prerequisite that only the account owner may act and that workspace grants do not apply, plus names alternatives (list_custom_domains for status reads).

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