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

Annotations already cover readOnlyHint, idempotentHint and destructiveHint, so the safety profile is done. The description adds useful domain context beyond that — what the returned fields are and how to interpret negative statuses, which the agent cannot infer from the enum alone.

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?

Two tight sentences, front-loaded with what is listed and immediately followed by the operative status interpretation. No filler or repetition of the title.

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?

There is no output schema, yet the description enumerates the returned fields (status, health score, warmup, limits) and names `statusMessage`, covering the essentials for a paginated read tool whose safety annotations are already complete.

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?

With 80% schema coverage the baseline is 3, but the description adds real interpretive value for the `status` enum: it explains that `failed` or `revoked` means the mailbox cannot send and points to `statusMessage`. That meaning is not present in the schema's unlabeled enum.

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 (List) and resource (connected sending mailboxes) plus the fields returned (status, health score, warmup, limits). The plural verb implies a collection read that contrasts with the sibling get_mailbox, though it doesn't explicitly name that alternative.

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?

Usage is implied — this is the tool for enumerating mailboxes — but there is no explicit guidance on when to use it versus get_mailbox or when to filter by status/tagIds. No exclusions or prerequisites are given.

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