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

The annotations already declare idempotentHint=true and destructiveHint=false, and the description adds meaningful behavior: it may reuse an existing chat, will not reactivate a departed membership, and returns chat_id and created. It does not cover permission requirements or failure modes, but it goes beyond the structured annotations.

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 primary action and eligibility constraint, then adds return behavior and the key alternative in only a few sentences. Every sentence adds useful information without repetition.

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 one-parameter operation with no output schema, the description covers eligibility, idempotent/reuse behavior, non-reactivation, return values, and the relationship to send_chat_message. The main remaining gap is that it does not explicitly identify or describe the user_id parameter, though the schema supplies its type and format.

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 0%, so the description must carry the semantic burden for user_id. It adds important eligibility meaning by saying the target must be an existing active consenting shared project collaborator and that departed memberships are not reactivated, but it never names the user_id parameter or explains its UUID format explicitly.

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 uses a specific verb and resource: 'Open or reuse a private direct chat' and scopes it to an existing active consenting shared project collaborator. It distinguishes this operation from inviting a new chat and from sending a message, so an agent can select it without opening sibling 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?

It explicitly states the eligible condition for use (existing active consenting shared project collaborator), a key exclusion ('Never reactivates a departed direct membership'), and names the alternative workflow for sending ('send_chat_message opens the chat itself'). This covers when to use it, when not to need it, and what it will not do.

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