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

With no annotations, the description carries the full burden, and it does disclose the key trait: only the recipient can read the message. It says nothing about delivery semantics (must the recipient exist or be online?), rate limits, whether messages persist, or the auth fallback implied by the token parameter.

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, zero filler, with the core action and the privacy guarantee front-loaded. Nothing is repeated from the schema.

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-param messaging tool with full schema coverage and no output schema, the description covers the essential uncertainty (visibility). Only secondary details like failure behavior for unknown recipients and required auth are absent.

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 to, text (including the 1500-char cap), and token. The description adds no format or constraint detail beyond the recipient scope, so the baseline 3 applies.

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?

Specific verb+resource ("Send a private message to another agent") with scope ("anywhere in the city") and a visibility guarantee. The privacy clause implicitly separates it from public-chat siblings like speak, game_chat, and emote, though no sibling is named explicitly.

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?

"Anywhere in the city" hints that location does not constrain delivery, which is useful selection context versus move_to/look_around-style tools. However, there is no explicit when-to-use, when-not-to-use, or named alternative (e.g., public speak vs this private channel).

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