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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered. The description adds genuinely non-obvious behavior: outputs are aggregate numbers only and never identify individuals, and teen-run or youth channels report positive totals only. 'Read only' merely restates the annotation, but the privacy rule and youth-channel quirk are real added value.

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 dense paragraph, front-loaded with 'measured in MEETUPS first' so priority of metrics is clear before the enumeration. It is long and somewhat run-on, but nearly every clause carries substantive information about output content or constraints.

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 an output schema present, return values need no explanation, yet the description still sets expectations about metric composition and trend comparison. Annotations handle the safety profile and the description handles scoping, privacy, and edge cases, leaving nothing an agent needs missing.

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%: period enum and channel resolution (channelId, @name, or name, omittable when exactly one channel exists) are fully documented in the schema. The description adds no parameter-level detail such as default period semantics beyond what the schema states, so the baseline 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 names a specific resource (one of the person's channels) and a specific measurement (reach), then enumerates the exact metrics returned: event attendance and first-timers per event and per month, sign-ups, views, unique people, reactions, and period-over-period trend. No sibling tool produces channel aggregate stats, so an agent can confidently select this one.

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 implied rather than stated: the agent can infer you call this to see how a channel is reaching people over the last 7d/28d. There is no explicit when-to-use/when-not, and no sibling is named as an alternative, although the schema points to list_my_channels for obtaining the channelId.

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