React to a WhatsApp message

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

The description explicitly exposes the two possible behavioral outcomes—adding a reaction or removing one via empty string—which goes beyond the annotations. It does not discuss auth or transform side effects, but the annotations already signal readOnly false and idempotent false, so this is adequate for the simple 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 sentence that front-loads the core action, immediately covers the edge case of removal, and uses no extra words. Every element is meaningful and directly useful to the agent.

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 simple two-parameter tool, full schema coverage, and annotations, the description is nearly complete. It might have benefited from a brief note on expected behavior or limitations, but nothing essential for successful invocation is missing.

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 already documents both parameters comprehensively, including message_id provenance and the empty-string behavior for emoji. The description adds no significant new parameter meaning beyond restating this, so the baseline score 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 clearly states a specific action ('add an emoji reaction') and resource ('a message'), and also covers the inverse case ('pass an empty string to remove'). This distinguishes it from sibling message tools like delete_message or send_message, which have different purposes.

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 intended use case is clear from the description, but there is no explicit guidance about when this tool should be used over siblings such as edit_message or send_message, and no exclusionary conditions. The usage is implied rather than directly stated.

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