conversations_add_message_attachments

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

Annotations already declare readOnlyHint=false (mutable), idempotentHint=true, and destructiveHint=false, so the description does not need to repeat these. However, the description adds no additional behavioral context, such as that attachments replace existing ones (mentioned only in the schema parameter description) or any auth or side-effect details. With annotations covering safety, a minimal description like this adds little value beyond the structured data.

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 extremely concise: a single sentence with no fluff. It front-loads the action and resource. However, it is so brief that it borders on under-specification, lacking any structural context that would guide an agent. Still, for conciseness alone, it is appropriately sized and well-front-loaded, so a 4 is reasonable.

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?

Given the tool's simplicity (2 parameters, no nested objects, no output schema), the description should still explain key contextual details, such as that it operates on an existing message and that attachments replace existing ones. Neither is stated in the description; the schema mentions replacement but not that it's for existing messages. The description is incomplete for an agent to fully understand when to use it.

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%: messageId is described as 'Message Id' and attachments as 'Array of attachment URLs to set on the message (replaces existing). Maximum 5 URLs.' The description does not add any meaning beyond the schema, so a baseline of 3 is appropriate. The schema already communicates the semantics effectively.

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 'Add message attachments' clearly states the action (add) and the resource (message attachments), matching the tool name. It is not a tautology and conveys the core purpose. However, it does not differentiate this tool from siblings like 'conversations_send_a_new_message' which might also include attachments, so it loses a point for not distinguishing the specific use case (attaching to an existing message).

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 provides no guidance on when to use this tool versus alternatives. There is no mention of prerequisites (e.g., message must exist), no exclusions, and no mention of related tools like 'conversations_add_an_inbound_message' or 'conversations_send_a_new_message'. The agent receives no context for selection.

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