google_ads_list_accessible_customers

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the read-only nature is covered. The description adds valuable behavioral context beyond that: it discloses the typical content ('just the MCC itself and any standalone accounts'), the exact return shape ({"resource_names": [...], "customer_ids": [...]}), and the ID format ('10 digits, no hyphens'). This gives the agent concrete expectations about the tool's output without contradicting the annotations.

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 three sentences, each earning its place: the first states the core purpose, the second adds context and the alternative tool, the third specifies the return format and ID format. It is front-loaded with the most critical information and contains zero filler. This is exemplary conciseness for a simple list tool.

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 list tool with an output schema (as indicated by context signals) and readOnlyHint/openWorldHint annotations, the description is fully complete. It covers the tool's scope, the typical response content, the exact return shape, and the ID format. The only missing elements (e.g., error cases, rate limits) are negligible for such a simple operation, and the description already routes to the sibling for the complex use case.

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 the input schema is trivially 100% covered. Per the rubric, a tool with 0 params receives a baseline of 4 because there is nothing for the description to explain. The description does not waste space on parameter details since none exist, and the schema itself leaves no gaps.

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 opens with a specific verb and resource: 'List every customer_id the OAuth user has direct access to.' It clearly distinguishes itself from the sibling tool google_ads_list_customer_clients by explicitly stating that this tool returns only direct-access accounts, not the full MCC tree. This makes the tool's purpose unambiguous and easily separable from its main alternative.

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?

The description provides explicit usage guidance: it states the tool returns a 'small, cheap list' and then directly instructs, 'For the full tree of accounts under the MCC (agency use case), call google_ads_list_customer_clients instead.' This tells the agent exactly when to use this tool versus the sibling, including the scenario where the alternative is more appropriate.

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