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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the description is not carrying the safety burden. It still adds meaningful context beyond them: a 100-post scope ceiling, platform-attributed historical data, a plan-tier gate, and the wrapped GET endpoint. Return format and pagination behavior remain undisclosed.

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 definition is a tight set of front-loaded fragments with no filler, and the most important mode switch (omit postId) appears early. The '[read-only]' prefix and the endpoint parenthetical duplicate information the agent already has from annotations and add little.

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?

With three optional parameters and no output schema, the description should carry more of the return-value burden, but it only gestures at 'metrics and roll-ups' without saying what a roll-up record contains or how comparison across reruns is presented. The plan gate and post cap are covered; the result shape is not.

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 postId, brandId and includeReruns are already documented in structured fields. The description restates the postId omission rule and the rerun comparison intent rather than adding syntax, defaults, or edge-case meaning. Baseline 3 applies when the schema does the 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 states a specific resource: per-account metrics plus tag, campaign, experiment and series roll-ups, and discloses the underlying endpoint (GET /api/v2/analytics/instances). It does not distinguish itself from analytics siblings such as get_analytics, query_insights or ads_insights, so an agent must infer when this comparison tool is the right one.

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 concrete conditional guidance: omit postId for scope-wide roll-ups capped at 100 posts, and set includeReruns to compare bookings of the same content over time. It also states a prerequisite (Pro plan or higher). What is missing is any exclusion or named alternative, so the when-not half of the guidance is absent.

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