AI agents call find_extrinsics to retrieve information from Substrate MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool retrieves and lists extrinsics (transactions/operations) from the blockchain, which is a read-only query operation. It has no capability to create, modify, delete, or execute code. The blast radius of misuse is minimal — an AI agent querying extrinsic data cannot harm the system or cause unintended side effects.
From the tool's definition Tool name is 'find_extrinsics' and description states 'Find extrinsics in the latest block' — this retrieves/queries extrinsic data from a block with no side effects or state modification.
Documented attack patterns abuse exactly the kind of access find_extrinsics gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Substrate MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for find_extrinsics:
{
"version": "1",
"default": "deny",
"tools": {
"find_extrinsics": {}
}
}find_extrinsics is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Find extrinsics in the latest block. It is categorised as a Read tool in the Substrate MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Substrate MCP Server MCP server in PolicyLayer and add a rule for find_extrinsics: 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 Substrate MCP Server. Nothing to install.
find_extrinsics is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the find_extrinsics 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 find_extrinsics. 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.
find_extrinsics is provided by the Substrate MCP Server MCP server (thomasmarches/substrate-mcp-rs). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Substrate 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.
13 Substrate MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.