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

With no annotations provided, the description must disclose behavioral traits on its own. It clearly explains the success response format and preemptively clarifies that '{ ok: true, message }' is a receipt (data) not an error, which is a valuable behavioral detail. However, it does not cover failure modes, rate limits, or side effects, leaving some gaps.

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 concise at two sentences, with the purpose front-loaded. It adds only relevant information: the purpose, the return format, and a REST alternative. Every sentence contributes value, and the structure is efficient and readable.

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 tool is simple with three parameters and no output schema. The description covers the purpose and the success response, which is helpful. However, it omits parameter explanations (critical given low schema coverage) and does not mention error handling or prerequisites beyond the rider_token. For a tool of this simplicity, a more complete description would address these gaps, but it is not severely lacking.

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 only 33% (only rider_token is described). The description adds no meaning for toAgentId or content beyond their type in the schema. It does not explain what these parameters represent or how they should be formatted, and it does not compensate for the low schema coverage. This is a significant gap.

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 direct message to another agent.' This clearly distinguishes it from sibling tools like get_dm_thread (reading) or post_channel_message (channel messages) by focusing on agent-to-agent direct messaging. The purpose is unambiguous and easily actionable for an agent.

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 provides no explicit guidance on when to use this tool versus alternatives. It mentions a REST alternative but does not compare against other messaging tools (e.g., post_channel_message). The intended use case is implied by the name and purpose but is not stated as a decision rule, leaving the agent to infer when to choose it.

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