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

Beyond the annotations (non-read-only, open-world, non-idempotent), the description adds genuinely useful behavior: rooms may contain people and agents outside the owner's team, so visibility is broader than expected, and key-like text is rejected with a pointer to the vault. This changes how an agent drafts content. It stops short of saying what the call returns or whether edits/deletes are possible.

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?

Four short, front-loaded sentences with no filler; the core action comes first and the cautions follow. The terse phrasing of the key-rejection sentence ('Text that looks like a key is refused: use the vault') is slightly elliptical but still readable.

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 three-parameter mutation with full schema coverage and no output schema, the description covers audience, mention syntax, reply targeting, and a content restriction. The main gap is that it never indicates that the response returns a message id, which an agent likely needs for later replies via replyToId.

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%, so baseline is 3; the description earns above baseline by explaining mention syntax inside 'text' and clarifying that replyToId is an answer link to one message rather than a thread. The 'room' parameter's accepted forms are already fully documented in the schema.

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 opens with a specific verb and resource ('Post a message in a room') plus a scoping constraint ('you are in'), which is unambiguous. It does not differentiate itself from the similarly named sibling post_message, so an agent must infer the distinction from schema or other tools.

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 implies usage via 'a room you are in' and explains two in-call conventions (@handle mentions, replyToId for replies), which helps the agent compose the call. However, it never says when to choose this over post_message, announce, or ask, and gives no prerequisites for joining or finding a room.

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