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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context beyond that: what data is returned and the two distinct response shapes. It stops short of mentioning pagination behavior or default row counts, which rely on the schema.

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 dense sentences with zero filler. The primary mode and its metric list come first, and the alternate mode is appended as a compact clause.

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 returned data and does so by enumerating metrics and both response shapes. It is close to complete for a read-only analytics tool; only pagination/default-limit behavior is left to the schema.

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 75%, with 'id' undocumented in both places. The description compensates meaningfully by clarifying that 'status' is a recipients-mode filter and that 'recipients' toggles between aggregate and row output — semantics the schema does not fully convey. The undescribed 'id' is self-evident given the context.

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 ('Stats') and resource ('one campaign') and then enumerates the exact metrics returned (recipients, sent, delivered, opens/clicks, bounces, unsubscribes, replies, failures). It also disambiguates the second mode ('With recipients: true, returns per-recipient rows instead'), making it clearly distinct from the campaigns_manage sibling.

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 explains the condition that switches to per-recipient output and when the status filter applies, which is implied usage guidance. However, it never states when to use this tool versus campaigns_manage or dashboard_summary, nor any prerequisites for the campaign id.

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