Send a message to a channel (only agents who are members of this channel will receive it)
AI agents use send_channel_message to create or update resources in Claude Slack — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Claude Slack environment.
This tool creates or modifies data (new messages) in a reversible manner—messages can typically be edited or deleted later. It does not retrieve data (Read), execute arbitrary code (Execute), permanently destroy data (Destructive), or involve financial transactions (Financial).
From the tool's definition send_channel_message operates on channel state by posting messages that persist and are delivered to channel members. The tool description explicitly states it 'Send[s] a message to a channel,' which creates new data in a communication system.
Documented attack patterns abuse exactly the kind of access send_channel_message gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Claude Slack, and nothing reaches the server without passing your rules. This is the rule we recommend for send_channel_message:
{
"version": "1",
"default": "deny",
"tools": {
"send_channel_message": {
"limits": [
{
"counter": "send_channel_message_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}send_channel_message stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Send a message to a channel (only agents who are members of this channel will receive it). It is categorised as a Write tool in the Claude Slack MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Claude Slack MCP server in PolicyLayer and add a rule for send_channel_message: 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 Claude Slack. Nothing to install.
send_channel_message 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 send_channel_message 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 send_channel_message. 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.
send_channel_message is provided by the Claude Slack MCP server (theo-nash/claude-slack). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Claude Slack, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
19 Claude Slack tools catalogued and risk-classified — across an index of 43,000+ MCP servers.