Estimate audience and delivery

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

Annotations already declare readOnlyHint and openWorldHint, but the description adds a genuine operational constraint not present in structured data: a 10-requests-per-minute rate limit. It also lists the returned metrics (impressions, clicks, conversions, reach), useful given there is no output schema.

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?

Two tight sentences with the core purpose front-loaded and the rate limit appended. No filler; every clause carries information.

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 read-only estimation tool with no output schema, the description supplies the return metrics, the planning context, and the rate limit. The notable gap is sibling routing (no mention of suggest_bid/get_channel_reach despite a dense sibling set), but otherwise it is sufficient to call correctly.

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 and the nested data object in detail. The description adds no further parameter semantics (e.g., how objective or goal_value affects the estimate), so the baseline 3 applies.

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?

It states a specific verb+resource ('Estimate audience size and delivery') scoped to 'a planned ad group' and enumerates the returned metrics. It does not explicitly differentiate itself from estimation-adjacent siblings like reddit_ads_suggest_bid or reddit_ads_get_channel_reach, leaving that to inference.

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?

'for a planned ad group' implies the pre-launch planning context, and the rate limit hints at intended usage, but there is no explicit when-to-use/when-not guidance and no alternative tool is named. Usage is implied rather than stated.

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