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

Annotations already declare readOnly/idempotent/non-destructive, so the description adds real value with 'READ (account key)' — an auth-scope requirement not in the annotations — and the 366-day range ceiling. It doesn't mention pagination or response shape, but the added auth and range context clears the bar.

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?

A single front-loaded sentence that leads with the READ classification and then the resource and scope. Every clause carries information; nothing is padded.

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-only stats tool with full schema coverage and rich annotations, the description covers access mode, scope, and range limit. Without an output schema, 'delivery and engagement counts' gives only a rough sense of return content, which is the one modest gap.

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%, with both `from` and `to` documented as YYYY-MM-DD UTC, so the schema carries the burden. The description's 'over a date range, up to 366 days' reinforces the constraint but adds no format or syntax detail beyond what the schema states.

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 specific verb (aggregate) and resource (delivery and engagement counts across sub-accounts) with a scoping qualifier (date range). It implicitly distinguishes itself from sendpost_get_subaccount_stats by saying 'across sub-accounts', but never names the sibling directly.

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 'up to 366 days' line implies the valid window, and 'across sub-accounts' implies aggregate use versus per-subaccount tools. However, it never explicitly says when to pick this over sendpost_list_account_stats or sendpost_get_subaccount_stats, leaving selection to inference from names.

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