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

Annotations already establish readOnly, idempotent and non-destructive, so the safety profile is covered. The description adds genuine domain context beyond the structured fields by explaining what the returned items are and their lifecycle state (not-yet-contacts, awaiting a triage decision), which helps the agent interpret results.

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?

A single tight sentence with zero filler, front-loading the location ('The inbox's External tab'). It is a sentence fragment lacking a verb, which is slightly less self-contained than an explicit 'lists ...' statement, but nothing is wasted.

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-required-parameter list tool with full schema coverage and complete annotations, the description supplies the missing conceptual context (what the External tab is and why items sit there). No output schema exists, but for a simple listing the description does not need to detail return shape.

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 100%: limit and productId are both documented in the schema, including defaults and bounds. The description adds no syntax or scoping detail about either parameter, so the baseline 3 is appropriate.

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 identifies the resource precisely as the inbox's External tab and characterizes its contents (support email from non-contacts awaiting triage). It implicitly distinguishes itself from the related action siblings (move_external_mail_to_inbox, mark_external_mail_spam, delete_external_mail) by naming those states, though it never states the verb 'list' explicitly.

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: the items are described as 'waiting to be moved into the inbox, marked as spam or deleted', which signals this is the triage queue to inspect before acting. However, there is no explicit when-to-use/when-not guidance or a named alternative (e.g., list_conversations) for agents deciding where to look first.

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