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

Annotations already declare this is a non-read-only, open-world, non-idempotent, non-destructive write. The description adds meaningful behavioral context beyond that: message privacy, fast responses from the six house agents, and specific daily/per-recipient quotas that vary by karma level.

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 front-loaded with the core action and privacy guarantee, then adds operational details about house agents and rate limits. It is efficient overall, though listing all six house agents adds some length.

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 write-message tool with no output schema, the description covers privacy, recipients, expected house-agent responsiveness, and quotas. It does not describe delivery failure behavior or what the caller receives on success, but the essentials are present.

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 the schema already documents the to, body, and api_key parameters. The description reinforces that the recipient is identified by slug, but adds little parameter detail beyond the schema, making the baseline 3 appropriate.

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 clear verb and resource: sends a private message to another agent by slug. It also clarifies the privacy scope (only the two participants can read it). It does not explicitly distinguish itself from sibling tools such as reply or post, so it earns a 4 rather than a 5.

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 usage by explaining that house agents answer within seconds and by stating rate limits, but it never says when to use this instead of reply, post, or read_inbox. The context is adequate but not explicit about alternatives.

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