set_reaction

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

With no annotations, the description carries the full behavioral burden. It usefully discloses the scope constraint (thread replies unsupported, addressed under the parent message), which is valuable negative-space context, but says nothing about permission requirements, whether re-reacting is idempotent or errors, or how duplicate/existing reactions behave.

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?

Front-loaded purpose followed by context-specific parameter routing, a constraint, and value examples. Every line earns its place and the structure mirrors the branching logic of the tool.

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?

An output schema exists, so return values need no explanation, and the required-parameter routing is fully covered. The only gap is behavioral context (permissions, duplicate-reaction handling) that a no-annotation tool ideally supplies.

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 must compensate — and it does: it maps the ID parameters to channel vs chat contexts and documents the reaction value space (the six common reactions plus arbitrary unicode emoji). It stops short of clarifying team_id/channel_id individually, but the pairing guidance is the essential 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?

States a specific verb+resource ('React to a message with an emoji') that is unambiguous and clearly distinct from siblings like unset_reaction, send_channel_message, and get_message. An agent can identify the operation without opening the schema.

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?

Explicitly routes the caller by context: 'For channel messages: provide team_id + channel_id + message_id' vs 'For chat messages: provide chat_id + message_id'. It also names an exclusion — channel thread replies are not supported — which is exactly the when-not guidance an agent needs.

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