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

Annotations already cover readOnly, idempotent, non-destructive, closed-world, so the bar is lower; the description still adds real value by explaining the `can_send` flag semantics and the reconnect-only-receive case. It doesn't state auth prerequisites or whether reconnecting is done elsewhere, a minor gap.

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 short sentences ordered by importance: what it lists, how to use the result, then the one non-obvious field. No filler and nothing buried.

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 zero-parameter read tool with an output schema and full annotation coverage, this is complete — the description covers purpose, downstream linkage, and the one field whose semantics an agent would otherwise misread.

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 tool takes zero parameters, so the baseline is 4 by rule. The description usefully explains the meaning of an output field (`can_send`) and the downstream use of `id`, which goes beyond structured data.

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+resource ('List the mailboxes...connected') with scope ('the current user', 'in this workspace'), which cleanly separates it from the list-emails-tool sibling that lists messages rather than accounts. An agent can pick the right one 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?

Explicitly routes the agent forward: use the returned `id` as `connected_account_id` when drafting or sending, which links this tool to create-email-draft-tool/send-email-tool. It stops short of saying when NOT to call it (e.g., caching vs. re-checking before send), so it is not a full 5.

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