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

Annotations already declare destructiveHint=true and idempotentHint=false, so the safety profile is known. The description adds real value beyond them by enumerating exactly what is destroyed (local MLS keys, messages, device identity) and what is left untouched, which is the key information an agent needs before an irreversible call.

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 tight sentences with the destructive scope front-loaded and the exclusions second. Every clause carries distinct information; nothing is repeated from the schema or annotations.

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 two-parameter destructive tool with no output schema, the definition covers what is destroyed, what is preserved, and the confirm guard is documented in the schema. Minor gaps remain, such as whether the caller must own the session or what happens to in-flight state, but the essentials for correct invocation are present.

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 100% and both parameters carry their own descriptions ('explicit caller intent to destroy this ephemeral session', 'isolated, ephemeral encrypted participant session'). The description adds no per-parameter meaning beyond the schema, 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 opens with a specific verb and resource — 'Permanently close one ephemeral participant session' — and immediately scopes what is destroyed. This clearly separates it from siblings like room_leave and room_end, which operate on rooms or membership rather than a single ephemeral session.

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 states the negative cases explicitly ('does not delete the room or automatically remove the member from other participants'), which implicitly routes the agent to room_end or room_leave for those outcomes. It stops short of naming those alternatives by name, so the selection guidance is clear but not fully explicit.

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