Get permitted sender choices

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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds genuine context beyond that: the result is a policy intersection, subdomains need separate authorisation, and permissions are revalidated at send time — material facts an agent would otherwise not know.

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 sentences, no padding, but front-loading is weak: it opens with a dense 'Intersects...' clause instead of stating the tool's output, and the acronym-heavy policy jargon costs more effort than it saves.

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?

An output schema exists, so return-value details are unnecessary, and the annotations cover the safety profile. What's missing is the plain statement of what the tool yields and how it differs from the unprefixed duplicate sibling, which for a 3-param read tool leaves a noticeable gap.

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 coverage is 100%, so every parameter is documented in the schema itself. The description adds nothing about mailbox_id scoping, delivery_group_id filtering, or the ETag/304 behavior beyond what the schema provides, so the baseline 3 applies.

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 explains the computation ('intersects current team, inbox and credential policies with provider restrictions') but never plainly states that the tool returns the set of sender addresses/identities the caller may use. The agent must infer the output from the title 'Get permitted sender choices' rather than from the description itself. It also doesn't distinguish this tool from the sibling mailbox_get_sender_choices.

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?

The closest thing to guidance is 'Sending checks these permissions again before submission', which hints this tool is consulted before sending, but no explicit when-to-use, when-not-to-use, or alternative is named. A near-duplicate sibling (mailbox_get_sender_choices) exists with no routing hint.

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