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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds the useful detail that the list is dynamic ("plus active ones"), but says nothing about ordering, stability, or whether results change as rooms open and close.

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?

A single front-loaded clause with no padding — the verb and scope come first. The parenthetical is slightly cryptic ("plus active ones" is unexplained), which keeps it below 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 zero-param read tool with annotations and no output schema, the description is close to sufficient — the returned item type (rooms) is clear. What's missing is whether the returned room names are the identifiers expected by lobby_read / lobby_post / lobby_send, which matters given the sibling set.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly signals that no filtering input is available.

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+resource ("list rooms") scoped to a named lobby and enumerates example rooms, so the agent knows exactly what comes back. It does not, however, contrast itself with the nearby lobby_directory or lobby_inbox siblings, which also surface lobby-related listings.

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?

There is no guidance on when to call this versus lobby_directory, lobby_inbox, or lobby_read — the agent must infer that this is the discovery step before reading or posting. No prerequisites or exclusions are stated.

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