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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds that the aggregation grain is per-mailbox and enumerates the returned metric categories, which substitutes usefully for the absent output schema. It does not mention pagination, rate limits, or whether metrics are totals versus per-period series.

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 sentences, zero filler, with the metric/scope definition front-loaded before the sibling disambiguation. Every clause carries information the agent needs for selection.

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 two-parameter read tool with a nested range object and no output schema, the description supplies the metric list that would otherwise be unknown, which is the main gap. Remaining minor omissions are return shape per period and whether `range` omission yields a documented default — the schema does cover the latter.

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%, including the nested `range` object with its `from`/`to`/alias fields and the backend-default behavior when omitted. The description only restates the grains ('one mailbox', 'date range') without adding format or aliasing detail. Baseline 3 applies since the schema carries the load.

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 first sentence names the exact metrics (sends, opens, clicks, bounces) and the exact aggregation grain (one mailbox over a date range), so an agent knows precisely what the tool returns. The second sentence explicitly separates it from the campaign-grain sibling `analytics_campaign`. No ambiguity with `email_account_get` or `analytics_account` remains.

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 states the selecting condition — 'the right view when diagnosing deliverability' — and routes the agent to `analytics_campaign` for campaign-grain numbers. Both the when-to-use and the alternative are spelled out rather than implied. This is exactly the routing guidance an agent needs when several analytics tools are siblings.

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