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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), yet the description adds substantial context beyond them: pagination defaults/caps, exactness of search, channel inference rules, the removability constraint keyed to reason=manual, and a precise note that read-only calls like this are NOT gated by the Send Message module while writes are. That last point is exactly the kind of non-obvious behavior an agent needs.

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?

Dense and front-loaded — it leads with what the list is, then pagination, then search semantics, then the removal caveat and the 403 warning. Every sentence carries operational information; nothing is 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?

With no output schema, the description compensates by describing what each row carries (a reason) and its only actionable facet. Combined with the 403 troubleshooting and pagination behavior, an agent has everything needed to call and interpret this tool.

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 the baseline is 3, but the description earns more: it specifies that search takes ONE EXACT address (not a partial match) and that a value containing @ without a channel is treated as email while anything else is SMS. That inference rule is genuinely additive beyond the schema's field definitions.

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 specific verb (List/fetch) and resource (account do-not-contact list) and enumerates exactly what populates it: unsubscribes, STOP replies, complaints, bounces, and manual adds. An agent can distinguish this from add_suppressions/remove_suppression without opening any schema.

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 concrete guidance: check the reason before promising a suppression can be undone, and diagnose 403s by looking for other causes rather than assuming the module is off. It stops short of naming remove_suppression as the alternative for the manual case, so routing is implied rather than explicit.

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