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

Annotations already cover readOnly/idempotent/non-destructive, so the description's value-add is the error condition ('an alarm the person is not on returns an error') and the guaranteed ordering of results. It doesn't mention pagination or result-size limits, which is the remaining behavioral gap.

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?

Front-loaded with purpose and ordering, then a scoping clause, then scope of returned data, then the error case. Slightly padded by 'Usernames only, nothing else about anyone,' which partially restates the first sentence's field list, but every sentence contributes.

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 correctly describes return values (usernames plus join day, in creator-then-newest order) and the failure mode. It is complete enough to invoke correctly; only pagination/truncation behavior for large alarms is unaddressed.

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% for the single UUID `id` parameter, so the schema carries the parameter documentation. The description adds no format, constraint, or auth detail about the id beyond what the schema states, making baseline 3 appropriate.

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?

Specific verb+resource ('Lists everyone on an alarm') plus the returned fields (username, join day) and sort order (creator first, then newest). It also distinguishes itself from the pending-request sibling by stating 'people still asking to join are a separate list.' An agent can identify this tool without opening a schema.

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?

Gives a clear usage condition ('For people already on one alarm') and explicitly excludes the adjacent case (pending join requests). It stops short of naming the sibling tool list_join_requests, so the routing signal is descriptive rather than a direct pointer.

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