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

Annotations already declare the tool read-only, idempotent, non-destructive, and closed-world. The description adds useful context by stating that it returns Siren's audience knowledge, size, and status, and that creating audiences happens elsewhere on the Ads page. It does not discuss freshness or pagination, but output schema and annotations cover much of that burden.

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 description is two short sentences with no wasted words. It front-loads the resource, then what data is available, then the read-only boundary.

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-parameter, read-only tool with an output schema and rich annotations, the description provides enough scope and boundary information. It could be slightly more explicit that it lists all audiences, but nothing critical is missing.

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?

The tool has zero parameters, so there are no parameter semantics to explain. Per the baseline for a zero-parameter tool, a 4 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 clearly identifies the resource as Meta customer list and lookalike audiences and states what information is returned: audience count, size, and status. It lacks an explicit verb and does not distinguish itself from any sibling ad tools, but the purpose is still clear.

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 implies the tool is for reading audience data and clarifies that audience creation is done by a human on the Ads page. However, it does not state when to use this tool versus related siblings such as ad_performance or ads_overview, so usage guidance is only implied.

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