Adds a specified emoji reaction to an existing message in a Slack channel, identified by its timestamp; does not remove or retrieve reactions.
Part of the Slack server.
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AI agents use SLACK_ADD_REACTION_TO_AN_ITEM to create or modify resources in Slack. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call SLACK_ADD_REACTION_TO_AN_ITEM repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Slack.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"SLACK_ADD_REACTION_TO_AN_ITEM": {
"limits": [
{
"counter": "slack_add_reaction_to_an_item_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Slack policy for all 143 tools.
These attack patterns abuse exactly the kind of access SLACK_ADD_REACTION_TO_AN_ITEM gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Adds a specified emoji reaction to an existing message in a Slack channel, identified by its timestamp; does not remove or retrieve reactions.. It is categorised as a Write tool in the Slack MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Slack MCP server in PolicyLayer and add a rule for SLACK_ADD_REACTION_TO_AN_ITEM: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Slack. Nothing to install.
SLACK_ADD_REACTION_TO_AN_ITEM is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the SLACK_ADD_REACTION_TO_AN_ITEM rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for SLACK_ADD_REACTION_TO_AN_ITEM. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
SLACK_ADD_REACTION_TO_AN_ITEM is provided by the Slack MCP server (@modelcontextprotocol/server-slack). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 143 Slack tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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