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

Annotations already declare readOnlyHint=false and openWorldHint=true, so the agent knows this is a mutating, open-world operation. The description confirms it sends a message, but adds no further behavioral context such as delivery semantics, token/auth requirements, rate limits, or what happens on failure. With annotations covering the safety profile, this is adequate but not rich.

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 a single, front-loaded sentence with zero waste. Every word contributes to identifying the operation, and there is no filler or redundancy.

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 mutating messaging tool with full schema coverage and no output schema, the description is minimally complete. However, it omits how this differs from lobby_post, what the return behavior is, and any delivery or threading context, leaving an agent to infer too much.

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 all six parameters are already documented in the schema. The description's 'by id' phrasing aligns with the 'to' parameter but contributes no additional syntax, constraints, or meaning beyond what the schema provides.

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 by id'), making the core operation clear. However, it does not distinguish this from sibling tools like lobby_post or lobby_inbox, so an agent cannot fully differentiate its role without inspecting other schemas.

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?

There is no explicit guidance on when to use this tool versus alternatives such as lobby_post, lobby_inbox, or lobby_read. The phrase 'direct message' implies a one-to-one send, but the description never states exclusions, prerequisites, or the conditions that make this the correct choice.

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