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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states 'Reads from persistent stats,' which is a useful attribution indicating a read-only, historical data operation. However, it does not delve into potential data delays, granularity of the per-domain breakdown, or any constraints around the filters, so some opacity remains.

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 description is a single, well-structured sentence that leads with the action and resource, then immediately enumerates the key output categories. It is concise, front-loaded, and every word earns its place.

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?

Given the tool's simplicity and the absence of an output schema, the description lists the main return facets (delivery rate, bounce rate, per-domain breakdown, top bounce reasons) which gives a reasonable picture. It does not explain the optional parameters' interplay, but the schema covers those. Overall, it is sufficiently complete for an agent to understand what the tool offers.

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%, with parameter descriptions for domain, period, and account already providing meaning. The tool description adds no additional parameter-specific detail beyond what the schema states, so the baseline of 3 applies.

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 uses the specific verb 'Get' with a clear resource ('email usage statistics') and details the specific metrics returned (delivery rate, bounce rate, per-domain breakdown, top bounce reasons). This clearly distinguishes it from siblings like get_suppression_list or get_mailbox_status.

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?

The description implies usage context through its enumeration of statistics, so an agent knows it addresses email delivery/bounce analytics. However, it does not explicitly state when to use this tool over alternatives nor mention any exclusions or when-not-to-use scenarios, leaving the guidance implicit rather than explicit.

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