set_message_reaction

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

The annotations already indicate this is a write operation (readOnlyHint=false), idempotent, and non-destructive. The description adds the fact that emoji or custom emoji are supported, but it does not disclose behaviors like whether setting a reaction replaces existing ones or that an empty reaction removes it. This is a modest addition beyond the annotations.

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 exactly two short sentences, front-loaded with the action, and contains no redundant words. It is appropriately concise for the tool's simplicity.

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 has 4 parameters including an optional reaction and is_big flag, plus practical nuances (e.g., removing a reaction by omitting it), the description is too sparse to be complete. It omits critical usage context and leaves the agent to guess important behaviors, making it adequate but far from comprehensive.

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 coverage is low at 25% (only chat_id has a description). The description provides a brief note about the reaction parameter ('Use emoji or custom emoji') but does not explain is_big, message_id, or the optionality of reaction. This insufficiently compensates for the coverage gap, leaving several parameters without meaningful semantics.

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 purpose with a specific verb ('Set') and resource ('a reaction on a message'), making it easy to distinguish from sibling tools like send_message or edit_message_text. The additional detail about using emoji or custom emoji reinforces the purpose without ambiguity.

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 this tool is used when you want to react to a message, but it provides no explicit guidance on when to use it versus alternatives, nor any exclusions or prerequisites. The use case is clear but not elaborated.

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