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

Annotations already cover the safe-read profile (readOnly, idempotent, non-destructive), so the description correctly spends its budget on output semantics instead: churn excludes free unsubscribes, new-subscriber math includes cancellations, and revenue is annualized rather than cash received. These are exactly the misreadings an agent would otherwise make. It stops short of noting snapshot staleness, rate limits, or auth requirements.

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?

Front-loaded with the returned metrics, then the measurement point, then per-field caveats; every sentence carries information. It is dense to the point of being run-on, and the field caveats would scan better as separated clauses, but nothing is filler.

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 no output schema, the description carries the full burden of explaining returns, and it does so by naming the specific fields (subscribers_churned, subscribers_new, revenue_usd) and their non-obvious definitions. For a single optional enum parameter and a read-only snapshot tool, nothing material is left for the agent to guess.

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 coverage is 100% and the enum plus 'Default: 30d' are already in the schema, so the baseline would be 3. The description earns a point by explaining what the period actually anchors — totals are measured at the end of that window — which the schema alone does not convey.

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?

Opens with a concrete enumeration of the resource returned (total and paid subscribers, new subscribers, paid cancellations, estimated revenue) plus the measurement window, so the agent knows exactly what this tool produces. It is distinguishable from get_daily_stats by the 'totals at the end of the period' framing, though it never names that sibling explicitly.

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?

Usage is only implied: the '7, 30 or 90 days' period framing signals this is a coarse-grained aggregate tool versus daily stats. There is no explicit statement of when to choose this over get_daily_stats, get_audience_insights or get_post_stats.

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