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

Annotations already establish that this is not read-only and not destructive. The description adds meaningful behavioral context beyond those hints: the reply is visible to everyone with design access, and the tool returns the created reply along with its comment_id. This helps the agent set expectations for side effects and output.

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 compact and front-loaded with the core action, followed by relevant use cases, visibility behavior, and return value. Every sentence contributes information the agent needs; there is no filler or repetition of the schema.

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 simple, additive write operation, the description is complete: it states the action, the context in which to use it, the visibility side effect, and the return value. The remaining details, such as message length limits and design_id format, are already fully covered by the input schema.

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%, so the schema already documents all four parameters (design_id, comment_id, user_intent, message_plaintext). The description adds no parameter-specific details beyond referring to 'existing comment' and 'reply', so the baseline of 3 is appropriate.

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 opens with the specific verb 'Add' and the precise resource ('response to an existing comment in a Canva design'). This clearly distinguishes it from sibling tools like comment-on-design, which creates a new top-level comment, and list-replies, which only reads replies.

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 gives concrete use cases: answering a reviewer's question, acknowledging or clarifying feedback, continuing a discussion, and providing a follow-up. It does not explicitly name alternative tools or state when not to use this tool, but the 'existing comment' framing strongly implies the boundary against creating new comments.

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