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

Annotations already declare this as a non-read-only, non-idempotent, non-destructive, closed-world write. The description adds genuinely new behavioral context: messages are publicly visible to all players and content is unrestricted ("you may say anything, true or not"), which shapes how an agent should compose the body. It stops short of describing failure behavior when chat is disabled or what a successful send returns.

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, front-loaded with the action and the key visibility fact, with no filler. The only inefficiency is that "Talks to the other players" is vaguer than necessary for a one-sentence purpose statement.

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 simple two-parameter tool with no output schema, the description covers purpose and visibility but omits the 1000-character limit, whether an error occurs if the session's game has no chat, and any hint about delivery. Adequate but with clear gaps for a mutation tool.

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 50%: session_id is documented in-schema ("returned by start_game") while body has only structural constraints (1–1000 chars). The description adds nothing about either parameter, so the schema does all the work; the undocumented parameter is self-evident, which keeps this at baseline rather than below it.

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?

"Talks to the other players" plus "Messages are public" makes clear this posts a chat message to other participants, and the "in games with chat" clause scopes it. The verb is informal and the title ("Send a chat message") carries more precision than the description itself, but no sibling tool does anything similar, so disambiguation is not an issue.

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 "in games with chat" implies a precondition for use, but the description never states what to do when chat is unavailable, nor points to any alternative (e.g., suggest or make_move for in-game actions). Usage is implied rather than instructed.

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