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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower, and the description adds real value: output varies by role (host sees counts and attendee names, viewers see only their own status and public numbers). That is behavioral detail annotations cannot express. It does not cover auth requirements or data-freshness, so not a 5.

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?

Three sentences, front-loaded with the core answer, then role-specific detail, then the disambiguation rule. Dense but every sentence carries distinct information. The middle sentence is long but not redundant.

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 single-param read tool with full annotations and an output schema, this is complete: it explains both output modes, the absence of a 'maybe' state, and where to go for plans/meetups. An agent has everything needed to call it correctly.

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?

There is a single parameter with 100% schema coverage, and the description adds nothing about eventId beyond what the schema (which explains the id source) already provides. Baseline 3 is appropriate; the schema does the heavy lifting.

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 opens with a concrete verb+resource ("Who's coming to a channel event") and then splits the answer by the requester's relationship to the event (host/co-host vs. viewer). It is clearly the signup/attendance status tool and cannot be confused with creation or listing siblings like create_event or list_upcoming.

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?

It explicitly steers the agent away from non-event cases: "Channel events have no 'maybe' — for plans and meetups use get_plan." That is a clear alternative and condition. It does not, however, differentiate from the sibling who_is_coming, which sounds like an adjacent attendee-listing tool, leaving one obvious ambiguity unaddressed.

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