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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description still contributes real operational context beyond that: the 400-day cap, the account-time-zone date semantics, and the caveat that additive metric sets may not return reach and frequency. It does not describe pagination or how multiple accounts/entities appear in the response, so it sits mid-range rather than at the top.

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?

Dense but front-loaded: the verb, scope and date constraint come first, followed by metric-set routing. Every sentence carries information except the trailing credits/'free' note and the MCP input-object reminder, which are boilerplate rather than tool semantics.

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?

No output schema exists, so the description must carry the return semantics, and it does: it enumerates the metric classes returned and states that comparisons yield each entity's change. Combined with level, date-range and filter semantics, an agent has everything needed to call it 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?

Adds meaning well past the 75% schema coverage: dates are YYYY-MM-DD in the account's time zone, campaignIds narrows the read while entityIds only filters returned rows, and metricSet is given a decision rule rather than just an enum label. compareSince/compareUntil are explained as producing per-entity change. Minor gap: no guidance on whether compare pair must be equal-length or within the 400-day window.

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?

States a concrete verb and resource ('Reads one ad account's provider figures for an exact date range'), names both supported platforms, all four levels, and enumerates the returned metrics. It also anchors itself against the alternative ('any question about a period other than the synced window'), which separates it from metrics_daily-style siblings.

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?

Explicit selection rules: use it for periods outside the synced window, trends, or before/after; use compareSince/compareUntil for a second range; choose metricSet=additive for spend/conversion/efficiency and standard for reach/frequency/fatigue. The agent has a decision procedure with no inference required.

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