add_reaction

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

Annotations already declare idempotentHint=true, so the line about reacting twice changing nothing largely restates structured data. The description does add value by describing the payload shape ("mapping each reaction on the message to who used it") and implying mutation via "React," but adds no auth requirements, error behavior, or rate-limit context.

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?

One-sentence purpose plus tightly scoped Args and Returns blocks, front-loaded and free of filler. The Args entries are slightly terse but each 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?

For a single-mutation tool with an output schema present, the definition covers purpose, all parameters, and idempotent behavior. Auth/permission requirements and failure modes are the only meaningful omissions.

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 0%, so the description carries the full burden and does so: it documents all three parameters, clarifies token is a conversation token and message_id the target, and gives a concrete example ("👍") for the reaction format. Only the integer type/range of message_id and token sourcing remain unstated.

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?

States a specific verb + resource ("React to a chat message with an emoji"), which is unambiguous and easily separable from siblings like get_reactions or remove_reaction. It stops short of explicitly naming the inverse/related tools, so it is clear but not sibling-differentiating at the top level.

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?

There is no guidance on when to use this versus get_reactions (read) or remove_reaction (undo), nor any prerequisite/auth context. The only usage-adjacent statement, "Reacting twice with the same one changes nothing," is a behavioral note rather than a when-to-use rule.

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