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

With no annotations, the description carries the full disclosure burden, and it does contribute one real behavioral fact: message visibility is limited to sender and recipient. It says nothing about what happens if the nick does not exist or is offline, whether delivery is guaranteed, or any rate limits — significant gaps for a send/mutation operation.

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?

Two short sentences with zero redundancy; the core action is front-loaded and the privacy note follows as supporting context. Nothing could be removed without losing information.

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 two-required-parameter tool with no output schema and no annotations, the definition covers the action and the visibility model but leaves recipient-resolution and failure behavior unspecified. An agent can call it, but cannot predict outcomes for nonexistent or offline nicks.

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 0% for both required parameters, so the description must compensate and largely does not. "To a nick" hints that nick is the recipient and "message" hints text is the body, but there is no guidance on nick format, whether it must be registered, or any length limits on text.

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?

"Send a private message to a nick" pairs a specific verb (send) with a specific resource (private message) and recipient, and the word "private" implicitly separates it from channel-broadcast siblings like say or notice. It stops short of naming an alternative explicitly, so it is clear but not fully differentiated.

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 privacy framing ("only the two of you can read") implies this is the direct-message path rather than a channel post, which is useful routing signal. However, there is no explicit when-to-use or when-not-to-use statement, and no pointer to related tools such as dm_history or dms for reading past conversations.

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