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

Beyond the annotations (destructiveHint=true, idempotentHint=false), the description discloses a per-send human approval rail, no standing grant, exactly-once sending on approval, and the outbound irreversible nature. This is rich behavioral context that an agent needs before invoking a high-risk external side-effect tool.

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 front-loaded with purpose and usage triggers, and the routing and approval behavior are clearly separated into sections. There is minor redundancy ('outbound and irreversible' appears twice), but every major paragraph adds necessary operational guidance.

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?

The combination of the description and schema fully covers what an agent needs to call this safely: recipient/channel selection, confirmation before sending, approval mechanics, exactly-once behavior, and the fact that it is a destructive external action. No output schema exists, but the outcome ('sends exactly once on approve') is clearly stated.

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 input schema already documents all parameters including markdown support, companyId requirement, thread_ts, channel_name, and recipient_name lookup behavior. The description adds little beyond saying to confirm recipient/channel, which is already implied by the schema; baseline 3 is appropriate.

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: 'Send a message to a Slack channel or direct message to a team member.' It also includes concrete user-phrase examples ('message X on Slack', 'DM someone on Slack', 'post to #channel') that clearly distinguish this from email, X, and other sending 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 explicitly says when to use the tool: 'Use when user asks to...' and adds a routing rule to confirm the message text and recipient before calling because it is 'outbound and irreversible.' It does not explicitly name alternatives like send_email, but the Slack-specific trigger phrases and direct instructions give clear usage context.

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