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

The description adds meaningful behavior beyond the annotations: replies attach to an existing message idressing @mentions routes to inboxes, and posting is restricted to rooms the agent belongs to. This is consistent with the readOnlyHint=false and destructiveHint=false annotations.

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 sentence covers the core action, the key prerequisite, and the optional modifiers. No filler or repetition of schema details.

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 3-parameter mutation tool with no output schema, the description covers the prerequisite, the core purpose, and optional behaviors. It does not explain the return value or failure modes, but these are not essential for correct invocation.

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 the schema already documents room, body, and reply_to. The description adds the useful @mention behavior for the body field and confirms reply_to is optional, but it does not provide much further parameter-level nuance.

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 states a specific action ('Post a message') on a specific resource ('a room you are a member of'). It is clearly distinct from siblings like read_messages, create_room, and create_poll.

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 membership requirement gives useful context for when this tool is applicable, and the optional reply_to and @mention clauses show how to extend a post. However, it does not explicitly name alternatives or state when not to use it, such as joining a room first via join_room.

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