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

The waitlist fallback is a real behavioral trait not encoded in annotations (readOnlyHint=false) or fully in the schema. However, the confirm/preview gating is largely a restatement of the schema's own confirm description, and nothing is said about duplicate enrollment, capacity errors, or whether the member is notified.

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 short sentences, action first, with the mutation's key constraint in parentheses. Slightly redundant with the schema's confirm field description, which is the only thing keeping it from a 5.

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 three-parameter mutation with no output schema and only a readOnlyHint annotation, the description covers the two things an agent most needs before calling: it acts on a single session, and it previews until confirm:true. Remaining gaps (error cases, notification side effects) are secondary for this shape.

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 only 33% — sessionId and userId carry no descriptions at all, and userId is a bare $ref to sessionId. The description implies the mapping (member = userId, one session = sessionId) but adds no format, lookup, or constraint guidance to compensate for the coverage gap.

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?

Names a specific verb+resource pair ('Add a member to one class session') and scopes it to a single session, which separates it from bulk membership operations and from the inverse sibling remove_member_from_gym_class_session. It does not explicitly name a sibling, so it stops short of a 5.

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 waitlist clause implies usage ('waitlists if full') and the confirm gate tells the agent it must opt in, but nothing states when to use this versus mark_gym_class_attendance, search_gym_class_members, or the cancel/standing variants. Usage is inferable rather than prescribed.

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