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

Annotations only flag this as a non-read-only, non-idempotent, non-destructive, open-world operation; the description adds the crucial behavioral facts: it does NOT grant access, it files a human-approval request, it returns a request id, and it requires the `propose_policy` capability. That is real context an agent cannot get from the structured fields 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 with zero filler, front-loading the core action and the most important caveat (no direct access grant). Every clause earns its place.

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 2-parameter tool with a fully covered schema, the description supplies the missing pieces: the approval workflow, the return value (request id), and the required capability. With no output schema present, mentioning the returned id closes the main 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 description coverage is 100%, so both `address` and `inbox_id` are already fully documented in the schema. The description adds no format, validation, or syntax detail beyond what the schema provides, so the baseline of 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 states a specific verb and resource ('Propose adding an address to an inbox's send allowlist') and immediately clarifies the scope by noting it never grants access directly. This cleanly separates it from siblings like mailbuttons_send_email or mailbuttons_request_promotion.

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?

It gives a clear prerequisite ('Requires the `propose_policy` capability') and explains the outcome (a filed request for human approval), which tells the agent when this tool is the right choice. It does not explicitly name an alternative tool or an exclusion condition, so it stops short of a 5.

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