AI agents invoke run-relayer to trigger actions in Hyperlane 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 executes a relayer service, which is an external operation that will monitor blockchains and perform automated cross-chain actions. While not directly moving funds, a misconfigured or maliciously-instructed relayer could facilitate unauthorized message delivery or asset transfers between blockchains.
From the tool's definition Tool name 'run-relayer' and description 'Runs a relayer for specified chains' indicate execution of a relayer process.
Documented attack patterns abuse exactly the kind of access run-relayer gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Hyperlane MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for run-relayer:
{
"version": "1",
"default": "deny",
"tools": {
"run-relayer": {
"limits": [
{
"counter": "run-relayer_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}run-relayer 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.
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Runs a relayer for specified chains. It is categorised as a Execute tool in the Hyperlane MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Hyperlane MCP Server MCP server in PolicyLayer and add a rule for run-relayer: 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 Hyperlane MCP Server. Nothing to install.
run-relayer 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 run-relayer 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 run-relayer. 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.
run-relayer is provided by the Hyperlane MCP Server MCP server (suryansh-23/hyperlane-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Hyperlane 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.
6 Hyperlane MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.