Add an emoji reaction to a specific Slack message using channel ID and timestamp. Useful for acknowledging, voting, or tagging messages without posting a reply.
Add an emoji reaction (name without colons) to a message.
| Name | Required | Description | Default |
|---|---|---|---|
| emoji | Yes | ||
| timestamp | Yes | ||
| channel_id | Yes |
| Name | Required | Description | Default |
|---|---|---|---|
| result | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false and destructiveHint=false, telling the agent this is a non-destructive write. The description adds the emoji-format rule (name without colons), which is useful, but says nothing about idempotency (adding the same reaction twice), permission requirements, or failure modes.
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 well-formed sentence with the action front-loaded and no filler. It is efficient, though the brevity comes at the cost of the missing guidance noted elsewhere.
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 not be described. However, for a three-parameter mutation tool with zero schema descriptions, the definition should at least identify what channel_id and timestamp refer to; as written it covers only the emoji parameter.
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% and all three parameters are required but undocumented in the schema. The description clarifies only the emoji format; channel_id and timestamp are left entirely unexplained, so it does not compensate for the coverage gap.
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?
The description states a specific verb (add) and resource (emoji reaction to a message), so the agent knows exactly what the tool does. It doesn't explicitly name reactions_remove as the counterpart, so it falls short of full sibling differentiation, but the action is unambiguous.
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 alternatives such as reactions_remove, nor any prerequisites (channel membership, existing message, duplicate reactions). Usage must be inferred entirely from the tool name.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.