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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the description only needs to add context beyond that. It does: it summarizes the returned attributes (title, start time, entry readiness, live presence) and adds a privacy guarantee ("never reveals who is in the room") that the annotations cannot express. Error behavior for an invalid or expired code is not described, which keeps it below a 5.

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?

The definition is front-loaded with the core action and key provenance information, and every sentence contributes something (definition, code sources, return summary, privacy bound). The first sentence is dense with nested parentheticals, which slightly hurts scanability but does not add waste.

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 an output schema present, the description need not enumerate return fields, yet it still previews them for fast triage. Combined with a single fully documented parameter and rich annotations, the only absent piece is failure behavior for a bad or expired code.

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 the room_code property already carries the 5-character example, so the schema does the baseline work. The description still adds real meaning by explaining the code's provenance (create_watch_room) and the two URL forms (…/s/AB2CD and …room.html?room=AB2CD) an agent might have to extract it from.

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 uses a specific verb (looks up) and resource (watch party), defines what a watch party is by reference to create_watch_room, and states the lookup key is a 5-character code. An agent can immediately distinguish this from create_watch_room, update_watch_party, and cancel_watch_party.

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 names concrete questions the tool answers ("when does it start?", "is it open?") and explains where a valid code comes from, which gives clear context for use. It stops short of explicit exclusions — e.g., pointing to update_watch_party when the caller wants to change settings rather than inspect them — so a small inference remains.

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