setMessageReaction

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

With no annotations provided, the description carries the behavioral burden. It discloses the mutation, two important fail conditions, and the boolean return. It does not cover every edge case, such as all message-type exclusions, but the core behavioral profile is clear.

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?

Three short, high-value sentences with the action front-loaded. Each sentence earns its place: the core operation, key restrictions, and the return value. There is no filler.

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 fully described schema and the return value stated in the description, an agent has enough information to invoke the tool correctly. A few edge-case exclusions are not spelled out, which keeps it just short of perfect.

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 has 100% parameter description coverage, so the description does not need to repeat parameter-level details. It reinforces that the operation targets reactions on a message but adds no meaning beyond what the schema already provides.

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 names a precise action ('change') and a specific resource ('chosen reactions on a message'), which clearly distinguishes it from message-mutation siblings like editMessageText or deleteMessage. It also communicates the success return, helping an agent predict the outcome.

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 when-not conditions: service messages cannot be reacted to and bots cannot use paid reactions. It does not explicitly name alternative endpoints, but the method is unique enough among siblings that these exclusions are sufficient to guide selection.

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