Get the source code of a specific call node from the loaded CPG by the call id
AI agents call get_call_code_by_id 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.
The tool performs a read-only query operation on a static code analysis graph (Joern CPG). It retrieves and displays source code information based on an identifier, with no capability to modify code, execute operations, delete data, or cause side effects. This is a low-severity information retrieval function typical of code analysis tools.
From the tool's definition Tool description states 'Get the source code of a specific call node' - this is a retrieval operation that queries the loaded Code Property Graph (CPG) by ID and returns source code data without modifying or executing anything.
Documented attack patterns abuse exactly the kind of access get_call_code_by_id 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 get_call_code_by_id:
{
"version": "1",
"default": "deny",
"tools": {
"get_call_code_by_id": {}
}
}get_call_code_by_id is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get the source code of a specific call node from the loaded CPG by the call id. 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 get_call_code_by_id: 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.
get_call_code_by_id 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 get_call_code_by_id 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 get_call_code_by_id. 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.
get_call_code_by_id 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.