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

Annotations supply only readOnlyHint=false, so the description must carry behavioral weight, and it does add two real traits: recipient eligibility and a rate limit ("Частота ограничена"). However, it gives no specifics on the limit, no indication of what error or outcome occurs when the recipient is ineligible, and no delivery confirmation semantics, leaving meaningful gaps for a send operation.

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 short sentences with the core purpose front-loaded and the eligibility restriction immediately after. Slight redundancy with the schema's login description costs it a point, but there is no filler.

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 two-parameter chat tool with no output schema, the description covers purpose, recipient restriction, and rate limiting — enough to call it correctly. The length cap and content restrictions live in the schema, so their absence here is acceptable, though the lack of any error/failure behavior keeps it from being fully complete.

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%, with both login and text fully documented including the 240-character cap and the no-links/no-markup rule. The description's recipient constraint largely restates the login field's own schema description, so it adds little meaning beyond the schema; 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?

"Личное сообщение" names the resource and implies the send action, and the eligibility sentence makes clear this is a directed one-to-one message rather than a broadcast. It never names the sibling game_chat_say, so the agent must infer the contrast with public chat from the word "private" alone.

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 states a concrete precondition for initiating a conversation — the recipient must have written to your character first, or be a battle neighbor — which functions as an explicit when-you-may-use rule. It stops short of naming game_chat_say as the alternative for open/public messaging, so the routing decision is only partly supported.

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