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

Annotations only mark readOnlyHint: false, so the description carries the burden of behavioral disclosure. It discloses that posting is a mutation, that it happens as YouSpot, that it only works in invited channels, and that confirmation is required. It also details formatting support (markdown and Slack's own). It doesn't mention rate limits or error behavior, but for a simple post action the disclosed behavior is adequate.

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?

The description is three sentences long, each earning its place: purpose, prerequisite/alternative, and formatting/confirmation rules. The critical info (purpose and the list_slack_channels pointer) is front-loaded, and there is no filler. It is tightly written and easy to scan.

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 tool with no output schema and only minimal annotations, the description covers the essential context: what it does, how to find valid targets, formatting expectations, and a safety confirmation. It omits details like error handling when the bot is not invited or behavior for DM vs. channel, but those are secondary. The description is complete enough for an agent to call it correctly in most cases.

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 description coverage is 100%, so the baseline is 3. The description adds a useful pointer for channel_id ('use list_slack_channels to find ids') and implies thread_ts usage ('optionally as a reply in a thread'), but it does not add new meaning beyond the schema's own descriptions. It does not elaborate on team_id or text formatting parameters, so it stays at the baseline.

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 clear, specific verb-resource pair: 'Post a message to a Slack channel or DM as YouSpot', and adds the thread-reply option. It implicitly distinguishes itself from siblings like send_email and send_text_to_user by specifying Slack as the target, and even points to list_slack_channels for finding channel IDs, which clarifies its scope.

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 explicitly states the prerequisite that the bot must be invited to the channel, and directs the agent to list_slack_channels for IDs. It also gives a clear behavioral rule: 'Confirm with the user before posting anywhere others can see it.' This is actionable guidance that tells the agent when to use the tool and what to do before invoking it.

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