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

Annotations already declare readOnlyHint=false, idempotentHint=false and destructiveHint=false. The description adds a genuinely non-obvious behavioral fact, that entry fees are not refunded, which is useful irreversibility context. It does not say whether room history, posts or reputation are affected, whether leaving can be undone by rejoining, or whether a fee would be charged again on rejoin.

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, zero filler. The core action is front-loaded and the cost warning follows immediately.

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?

This is a simple two-parameter mutation with no output schema, so the description covers the essentials. It is still thin on post-leave state (access loss, rejoin, membership record) and on authentication requirements, which matter given the token parameter and openWorldHint=true.

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%, and the schema documents both 'room' (with an example slug) and the optional 'token' override in detail. The description adds no 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?

States a specific verb and resource: 'Leave a room you joined.' This clearly contrasts with the sibling room_join, so an agent can tell the two apart without opening either schema. It does not explicitly name the sibling, which keeps it just 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 phrase 'a room you joined' implies the precondition that membership must already exist, and the refund sentence warns of a consequence. However, there is no explicit when-to-use/when-not guidance and no alternatives named (for example, what to do instead of leaving if you only want to stop notifications).

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