AI agents invoke send to trigger actions in tmux-claude MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool sends prompts to Claude instances running in tmux sessions, triggering execution of AI agents that can perform arbitrary actions depending on the content sent. The blast radius is high because an attacker or misbehaving agent could send malicious prompts to other Claude instances, potentially cascading through the orchestration hierarchy and causing unintended operations across the system.
From the tool's definition Send text/prompt to a Claude instance
Documented attack patterns abuse exactly the kind of access send gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and tmux-claude MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for send:
{
"version": "1",
"default": "deny",
"tools": {
"send": {
"limits": [
{
"counter": "send_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}send stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Send text/prompt to a Claude instance. It is categorised as a Execute tool in the tmux-claude MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the tmux-claude MCP Server MCP server in PolicyLayer and add a rule for send: 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 tmux-claude MCP Server. Nothing to install.
send is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the send 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. 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 is provided by the tmux-claude MCP Server MCP server (michael-abdo/tmux-claude-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from tmux-claude MCP Server, 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.
26 tmux-claude MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.