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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful behavioral scope: what is included, what is excluded, and the limitation that PMax asset-group signals currently have no reading tool and must be checked in the Google Ads UI.

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 purpose is front-loaded, followed by relevant exclusions, then the workspace note. The parenthetical about PMax is slightly long but earns its place by preventing a likely wrong-tool selection.

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?

The tool is low-complexity with one optional parameter, read-only annotations, and an output schema. The description covers the resource scope, exclusions, the missing PMax-read path, and the only parameter, leaving no major gap for correct invocation.

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 0%, so the description carries the burden for the single optional parameter. It explains that workspace is the customer workspace slug and that it is optional when only one workspace exists, which adds meaning beyond the schema.

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 names the specific resource (Zielgruppenlisten/User Lists) and the exact granularity (USER_LIST criteria at campaign/ad group level). It also distinguishes the tool from adjacent audience categories and PMax signals, so an agent can identify what data this tool returns.

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 explicit exclusions for PMax asset-group signals and interest/in-market/custom audiences, and points to ads_add_asset_group_signal for writing PMax signals. It does not explicitly contrast with ads_list_customer_match_lists, but the main use/not-use boundaries are clear.

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