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

Annotations provide no safety or idempotency hints (all false), so the description carries the burden. It discloses the core behavior (add or remove a reaction) and the empty-reaction nuance. However, it does not mention potential limitations like the channel restriction (which is only in the schema) or any side effects beyond the action itself.

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?

Two concise sentences with no fluff. The primary action is front-loaded, and the secondary removal behavior is stated efficiently. Every word earns its place.

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?

With a complete schema (100% parameter coverage) and an output schema present, the description only needs to cover the essential behavior. It does that, including the removal nuance. It could mention the channel limitation, but that is already captured in the schema, so the description is sufficiently complete for an agent to invoke it correctly.

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 schema covers all parameters with 100% description coverage, so the baseline is 3. The description adds no extra parameter-level detail beyond what the schema already states; the only extra nuance (empty reaction removal) is also present in the reaction parameter's description.

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's function: reacting to a WhatsApp message with an emoji, and explicitly mentions the removal behavior with an empty reaction. The verb 'react' and resource 'WhatsApp message' are specific, distinguishing it from siblings like wa_send_message or wa_edit_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 implies usage (when you want to react to a message) but provides no explicit guidance on when to use this tool versus alternatives. It mentions the empty-reaction removal case, which is a specific usage guideline, but does not discuss exclusions or direct the agent to sibling tools for other actions.

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