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

The description states the connection is 'read-only', while annotations declare readOnlyHint=false and idempotentHint=false. That is a direct contradiction of the safety profile an agent relies on, even though the enumerated actions are in fact reads. The otherwise useful disclosure of where the remaining operations live cannot offset a conflicting safety claim.

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?

Three tight sentences with no filler, front-loaded with what the connection is before the action list and the off-tool routing note. Slightly dense parenthetical packing, but every clause earns its place.

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 one-parameter, no-output-schema tool this covers the main decision points: available actions, the domains prerequisite, and where the excluded operations live. It still leaves the shape of each response (what status returns, what a domains entry contains) entirely unspecified, which matters since no output schema exists.

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 description coverage is 0%, so the description must carry the meaning of the single action enum. It does: 'domains (verification state; check before choosing from_email)' explains both what the value returns and when to pick it, and 'status' is at least recognizable in context. Minor gap: it never spells out what status reports.

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?

Names the specific resource (the BYO Resend connection used for email campaigns) and enumerates the two supported actions, status and domains. An agent can distinguish it from siblings like sending_settings or email_send because the description explicitly says connecting, disconnecting, test sends and tracking happen elsewhere.

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 a concrete use condition — call domains and check verification state before choosing a from_email — and explicitly redirects the other related operations to the app under Settings > Email. It lacks a 'do not use this for X' exclusion, but the routing guidance is clear.

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