send_message

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It only states the basic action without mentioning side effects (e.g., that it appends to the thread), failure conditions (e.g., invalid thread_id), or any required permissions. This is a significant gap for a write 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?

The description is a single, focused sentence that directly conveys the tool's purpose without any wasted words. It is appropriately concise and front-loaded.

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 a small parameter set with full schema coverage and an output schema, so the description does not need to explain return values. However, because there are no annotations, the description is minimal and does not address potential edge cases or operational context, making it only adequately 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?

The input schema provides 100% coverage with detailed descriptions for all parameters, including the meaning of thread_id and the attachment size limit. The tool description itself adds no additional parameter context, so the schema does the heavy lifting, warranting the baseline score.

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 action ('Send a message'), the target ('a guest'), and the context ('on an existing conversation thread'). It is specific and distinguishes from sibling read-only tools like list_messages and get_message_event.

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 requiring an 'existing conversation thread', which suggests the tool is for replies rather than starting new threads. However, it does not explicitly mention when to use this tool over alternatives or provide exclusion criteria, so the guidance is only implied.

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