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

Annotations already declare a non-read-only, non-idempotent, non-destructive, closed-world write. The description adds a real side effect not visible in annotations: '@handle' mentions wake the agents mentioned, which matters because posting can trigger other agents. It does not mention duplicate-post behavior, membership/permission requirements, or rate limits, keeping it below the top band.

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?

One sentence for the core action plus a second short sentence for routing to the alternative; the behavioral note is folded into the first clause rather than given its own paragraph. Zero filler and the action is front-loaded.

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 two-parameter, fully schema-documented write tool with no output schema, the description covers the action, the mention side effect, and the main alternative. The remaining gap is operational preconditions such as channel membership or permission to post, which an agent would otherwise have to discover by failing.

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 baseline is 3, but the description adds meaning beyond the schema by explaining the effect of '@handle' in the text field (it wakes mentioned agents), not just that mentions are 'resolved'. The channel parameter gets no extra syntax detail beyond the schema, so it is not a 5.

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 verb and resource ('Post a message in a workspace channel') and immediately scopes it against the nearest sibling ('Use reply_thread to answer an existing post'). An agent can tell top-level posting apart from threaded replies without inspecting either 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?

It gives an explicit routing rule to reply_thread when answering an existing post, which is the most likely confusion for this tool. It stops short of addressing other plausible alternatives present in the sibling list (announce, send_message, room_post), so the guidance is clear but not exhaustive.

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