Set Chat Message Reaction

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

Annotations already indicate this is a mutating (readOnly=false), non-idempotent operation. The description adds that Unicode emoji and named reactions are supported, but does not disclose behavior such as replacing an existing reaction, duplicate reactions, or errors beyond what annotations convey.

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 filler. The core action is front-loaded, and the reaction-type detail is presented immediately after, making the definition easy to scan.

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 simple tool with complete schema coverage and relevant annotations, the description covers the core action and reaction format. However, it omits usage boundaries (e.g., removal via unset_chat_message_reaction) and any behavior on repeated reactions, leaving some selection context incomplete.

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 covers all parameters at 100%, so the baseline is 3. The description adds specific value for reactionType by enumerating supported named reactions and explicitly allowing Unicode emoji, which is not present in the schema descriptions.

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?

Description clearly identifies the verb ('Add') and resource ('a reaction to a message in a chat conversation'), and the 'chat conversation' scope distinguishes this tool from channel-reaction siblings. It also clarifies the two supported reaction forms.

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?

No guidance on when to use this tool rather than set_channel_message_reaction or unset_chat_message_reaction. An agent must infer the scope from the tool name and description; there is no explicit when/when-not guidance.

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