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

Annotations already declare destructiveHint=true and idempotentHint=true; the description earns credit by spelling out the real-world consequence (future campaigns are suppressed) and the hard constraint that numbers can never be opted back in. It stops short of describing partial-failure or duplicate handling, so the batch behavior remains partly opaque.

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 write marker is front-loaded, then scope, then irreversibility, then the use condition, then the endpoint. Every sentence carries information an agent needs, and there is no filler.

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 destructive, two-parameter write with no output schema, the description covers consequence, irreversibility, batch limits, and user-confirmation gating. Remaining gap is return/error behavior, such as whether invalid numbers fail the whole batch or are skipped, which a calling agent would want.

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 the schema already documents 'confirm' and the international-format requirement for 'numbers'. The description only restates the 1-to-25 bound that the schema already enforces via minItems/maxItems, adding no syntax or format detail beyond it. 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?

States the specific operation (adds phone numbers to the optout database), the batch bound (1 to 25), and the downstream effect (no later campaign is sent to them). This clearly separates it from the read-only sibling smseveryone_list_optouts.

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?

"Do it only when the user asks" gives an explicit gating condition requring user intent, and the irreversibility note warns against casual use. It does not name a sibling alternative, but the sibling set offers no competing write path, so the guidance is nearly complete.

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