Loads a CPG from a file if the cpg is not loaded or the cpg is not the same as the filepath.
AI agents call load_cpg to retrieve information from Joern MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Loading a CPG is a read operation that retrieves data from storage for analysis. It has no side effects on the underlying data and merely prepares an existing artifact for querying by other tools in this security analysis suite. The operation is idempotent and reversible (the file remains unchanged). This is characteristic of a Read category tool.
From the tool's definition Tool name is 'load_cpg' and description states it 'Loads a CPG from a file', which retrieves/reads a pre-existing Code Property Graph artifact from disk into memory. No data is created, modified, or deleted.
Documented attack patterns abuse exactly the kind of access load_cpg gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Joern MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for load_cpg:
{
"version": "1",
"default": "deny",
"tools": {
"load_cpg": {}
}
}load_cpg is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Loads a CPG from a file if the cpg is not loaded or the cpg is not the same as the filepath. It is categorised as a Read tool in the Joern MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Joern MCP Server MCP server in PolicyLayer and add a rule for load_cpg: 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 Joern MCP Server. Nothing to install.
load_cpg 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 load_cpg 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 load_cpg. 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.
load_cpg is provided by the Joern MCP Server MCP server (sfncat/mcp-joern). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 21 Joern MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
21 Joern MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.