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

No annotations are provided, so the description carries the full burden. It mentions that 'All PII must be SHA-256 hashed,' which is a critical behavioral constraint for data handling. However, it lacks other important details: whether this is a mutating operation (implied by 'Add'), potential side effects, rate limits, authentication requirements, or error conditions. The description adds some value but leaves significant gaps.

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 concise and front-loaded, stating the main purpose in the first sentence and adding necessary details in the second. Both sentences earn their place by providing essential information about the action and payload format. It avoids redundancy and is appropriately sized for a tool with two parameters.

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?

Given the complexity (a mutating tool with data privacy implications), no annotations, and no output schema, the description is partially complete. It covers the basic purpose and payload format but lacks critical behavioral details like permissions, side effects, or response expectations. The description compensates somewhat with payload specifics, but overall it is adequate with clear gaps for a tool that modifies user data.

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 both parameters ('audience_id' and 'payload') with descriptions. The description adds semantic context by specifying that the payload must be a JSON string with hashed user data and a schema array, including examples like 'EMAIL, PHONE, FN, LN.' This clarifies the purpose and format beyond the schema, but does not fully compensate for the lack of behavioral details. Baseline 3 is appropriate as the schema does heavy lifting.

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 states the specific action ('Add users to a custom audience') and resource ('custom audience'), distinguishing it from sibling tools like 'create_custom_audience' (which creates audiences) and 'remove_users_from_audience' (which removes users). The verb 'Add' is precise and the object 'users' specifies what is being added.

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 no guidance on when to use this tool versus alternatives like 'create_custom_audience' or 'remove_users_from_audience'. It mentions the payload format but does not indicate prerequisites, such as whether the audience must already exist or if there are limits on user additions. Usage context is implied but not explicit.

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