React to a message

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

Adds a non-obvious behavioral trait: passing an empty reaction list removes existing reactions. Annotations provide idempotency and open-world hints, but the description adds contextual behavior beyond those, though it does not cover auth or rate limits.

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 sentences, directly front-loaded with the primary purpose and a key usage note. No filler or repetition of schema details.

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?

With 7 parameters, no output schema, and minimal annotations, the description does not provide enough context about expected outcomes, parameter relationships, or when to choose this over sibling reaction tools. The empty-list behavior is useful but leaves many gaps.

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 below 50% (only emoji and customEmojiIds have descriptions). The description adds the concept of empty list to remove, but it is ambiguous which parameter it refers to and leaves other parameters unexplained.

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?

Clearly states the action (set reactions) and target (a message). The title 'React to a message' reinforces the verb+resource. It is distinct from siblings like get_message_reactions by focusing on writing reactions.

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?

Implied usage: use when you want to react to a message, with a specific pattern for removal (empty list). However, it does not explicitly distinguish from related tools like set_default_reaction or get_message_reactions, nor does it state when not to use it.

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