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

With no annotations, the description carries the full burden and does well: it discloses the sending identity (as the user), irreversibility ('it can't be unsent'), an authorization constraint (refused from the agent's own turn), and a lookup limitation (the connection can't resolve channels). It stops short of describing what a successful call returns or how an ambiguous/unknown recipient surfaces as an error.

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?

Front-loaded with the verb and scope, and nearly every clause carries a constraint the agent needs. The semicolon-chained phrasing makes it denser than it needs to be, but there is no filler sentence to cut.

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 3-parameter mutation tool with no annotations and no output schema, the description covers identity, scope, gate conditions, and irreversibility. It is only short of confirming what the agent sees on success (message ID/confirmation) or how a failed recipient lookup is reported.

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 only 33% — only `channel` is documented in the schema — but the description compensates: it defines `to` as a person's name, full name, or a first name unique in the workspace, and reinforces that `channel` is not supported. `text` is implicitly defined as the approved message body, which is thin but recoverable from context.

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?

States a specific verb and resource (send a Slack message) plus the exact scope: a DM with one person in the user's workspace, sent as the user. It explicitly carves out what this tool is NOT (channels can't be sent to), so an agent distinguishes it from any channel-posting expectation without opening the 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?

Gives a positive gating condition ('only a message the user approved, to the person they meant'), two explicit exclusions (channels are unsupported; calls from the agent's own turn are refused), and a named fallback action ('draft it for the user instead'). That is when-to-use, when-not, and the alternative in one compact block.

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