send_dm

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

Annotations already convey that this is a side-effectful operation (readOnly=false, destructiveHint=true), lowering the burden. The description adds real behavioral detail beyond annotations: blocks must be a JSON string, rich_text blocks are supported, and message acts as the plaintext fallback. It does not cover unfurl behavior, but nothing contradicts the annotations.

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?

Three sentences with no filler: the first states the action, and the next two concisely explain the optional block behavior and fallback semantics. Information is front-loaded and every sentence earns its place.

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 small side-effectful tool with an output schema and annotations, the core call semantics are covered: recipient, message text, optional rich formatting, and fallback behavior. The main gap is the undocumented unfurl parameters, but they have defaults and self-explanatory names.

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%, so the description must compensate. It does explain blocks (JSON string, rich formatting) and message (fallback role), but it says nothing about unfurl_links or unfurl_media, leaving those to inference from their names and defaults.

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 opening sentence, 'Send a direct message to a user', states a clear verb and resource. It implies a 1:1 user recipient, which helps distinguish it from channel-oriented tools, but it does not explicitly name siblings like post_message or send_group_dm.

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 description implies the appropriate context by saying 'to a user' and gives useful formatting guidance, but it never states when to prefer this tool over post_message, send_group_dm, or post_command. There are no explicit exclusions or alternative routing cues.

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