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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, and the description still adds real behavior: the required email:read permission, the guarantee that it never returns credentials, the fact it does not connect or enable collection, and the empty-list/owner_actions edge case. This is substantive disclosure beyond the structured fields.

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?

The opening sentence front-loads purpose and the entry-point cue, then each subsequent sentence carries a distinct fact (providers, permission, return shape, non-actions, empty-state). No filler or repetition.

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, no-output-schema tool this is complete: it explains prerequisites (email:read), the shape of a successful result, how to chain the returned IDs, and what an empty result implies. An agent needs nothing further to call it correctly.

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 per the rubric; there is no parameter nuance the description could add. It does describe the return payload (IDs, addresses, providers, sync status), which is useful given there is no output schema, but that is return semantics rather than parameter semantics.

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 precise verb+resource ('list the inboxes this AI may read') with the authorization scope made explicit, and enumerates covered providers (Gmail, Outlook/M365, QQ, 163, Exmail, IMAP). The 'Start here when the user asks about their email' framing positions it clearly against siblings like read_email and list_email_events.

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 an explicit entry-point condition ('Start here when the user asks about their email'), plus an explicit exclusion ('Does not connect mailboxes or enable collection'), and forwards the agent to the next step ('use its IDs in later calls'). When-to-use, when-not, and follow-on are all covered.

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