Add a Slack reaction

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

Annotations already declare idempotentHint=true, destructiveHint=false and openWorldHint=true, so safety and repeat-call behavior are covered. The description adds one genuinely useful behavioral fact beyond the annotations: the reaction is attributed to the bot, not the calling user. It says nothing about failure modes or permission requirements.

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?

A single tight sentence with the effect front-loaded and no filler. Every word 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 3-param, fully documented, annotation-backed tool, the description is nearly sufficient; the actor disclosure closes the main ambiguity. The remaining gap is prerequisites and error behavior, which matters less for an idempotent non-destructive call.

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 coverage is 100%, including a concrete emoji naming example ('thumbsup, eyes') and channel formats, so the schema carries the parameter semantics. The description adds nothing on top, which is the expected baseline here.

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?

Specific verb + resource ('Add an emoji reaction to a message') and it adds the actor identity ('as the bot'). It is clearly distinct from reactions_remove by name and verb direction, though it never names the sibling explicitly.

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 when-to-use guidance, no prerequisites (bot must be a member of the channel, reactions:write scope), and no pointer to reactions_remove for the inverse operation. Usage is only inferable from the name.

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