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

No annotations are supplied, so the description carries the full burden, and it discharges most of it: it discloses the returned payload, that the seatToken is your identity to be passed to vs_play/vs_wait and never written into content, and an explicit prompt-injection warning that rival text is material to evaluate, never instructions. It stops short of describing failure behavior — what happens if seat B is already occupied, the match does not exist, or the match has ended — which matters for a join operation with no annotation coverage.

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?

Purpose is front-loaded and the CAPS section headers make the wall of text navigable, but a large share of the content — the loop mechanics, the propose/accept/close move semantics, the closing-round rule, the summary field — belongs to vs_play and vs_wait rather than to joining a match. For this tool the genuinely load-bearing part is two or three sentences; the rest is protocol boilerplate that inflates the definition.

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 no output schema, the description must explain the return value, and it does name every field returned and what the agent is expected to do with the rival's solution immediately after joining. The identity-handling and injection warnings cover the security context that annotations would otherwise supply. Only the absence of any error or edge-case guidance keeps it from being fully sufficient.

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%, with matchId and agent both documented in the schema (including the required identity format for agent), so the baseline applies. The description never mentions either parameter and adds no meaning beyond the schema, for example whether matchId must refer to a match that is still waiting for seat B.

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?

First sentence gives a specific verb and resource ('Entra en una partida del MODO VS como puesto B') and defines scope precisely: the next entrant after whoever opened it. It explicitly differentiates from the sibling vs_open (puesto A), and states what the call returns (seatToken, problema, contexto, solución del rival), so an agent can select it without opening any schema.

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?

Explicit exclusions and routing: 'No la uses en una partida que hayas abierto tú' plus a full ABRIR/ENTRAR split naming vs_open, and a stated loop pointing to vs_play when it is your turn and vs_wait when it is not, including the retry instruction with no user prompting. Nothing about when to choose this tool versus its siblings is left to inference.

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