im_thread_reply

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

Since no annotations are provided, the description carries the full burden of disclosing behavioral traits. It reveals that the message is sent on behalf of the webhook owner and that thread creation is unsupported, which are key side effects. It does not cover error behavior or notifications, but for a simple write operation, this is reasonable disclosure.

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 a clear 'WRITE:' label that signals the operation type. It is concise, contains no filler, and effectively communicates the core action and constraint in minimal space.

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?

The tool has moderate complexity with four parameters, but the schema documents them well, and the description captures essential context: it is a write operation for existing threads on behalf of the webhook owner. The absence of an output schema is acceptable because the description focuses on the action and constraints. A minor gap is that it does not clarify behavior when parameter combinations conflict, but this is not critical.

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?

The input schema provides descriptions for all four parameters, achieving 100% coverage, so the tool description does not need to add extra parameter details. The description itself omits any mention of parameters, but the schema already offers clear semantics for dialog_id, message_id, and thread_dialog_id. This aligns with the baseline of 3 for high schema coverage.

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 clearly states the tool sends a message to an existing thread on behalf of the webhook owner, using a specific verb and target. The 'WRITE:' prefix and the explicit note that new threads are not created via REST distinguish it from read-oriented tools like im_thread_messages or im_chat_messages.

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 explicitly limits usage to existing threads, stating that new threads cannot be created via REST, which gives a clear boundary. However, it does not name alternative tools for sending new messages (e.g., im_send_message), so only implied differentiation from siblings is provided.

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