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

The annotations already cover the safety profile (read-only, non-destructive, closed-world), so the description's added value is in the aggregate-only nature ('counts only, never who') and the privacy suppression below 10 deliveries — a disclosure that directly affects how an agent should interpret missing click/open values. It does not cover auth scoping, data freshness, or retention windows.

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 'Read only,' then a dense but purposeful enumeration of metrics and the abTest caveat. Every clause carries signal, though the long comma-chained metric list is slightly harder to scan than a structured breakdown would be.

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 burden of describing return values and does so thoroughly, including the conditional abTest block and the suppressed-metrics case. The remaining gap is that the identifier's provenance and the report's time scope are unstated, which is minor for a one-parameter read tool.

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 0%, so the single campaignId parameter is documented only by its name and regex pattern. The description implies the identifier refers to a sent email but never says how to obtain it (e.g., from a campaign listing) or what happens with an invalid or non-email campaign id.

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 names a specific resource — the performance report of an email that went out — and enumerates its contents (sent, delivered, bounces, complaints, unsubscribes, clicks, opens, clicks per link, time series, abTest breakdown). That enumeration clearly separates it from a plain campaign-fetch or account-level analytics tool, though it never names a 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: it is the tool for metrics on an email that has already gone out, versus campaign configuration or drafting. There is no explicit statement of when to prefer it over a broader analytics tool, and no prerequisites or exclusions are given.

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