extract_function
Extract a line range out of an enclosing function into a new named helper (AST-aware, TypeScript/JavaScript). Computes the parameter list via free-variable analysis and a return value from bindings used after the slice. The helper is inserted after the enclosing function; the slice becomes a call...
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What extract_function does on Trace
AI agents call extract_function to retrieve information from Trace without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Why extract_function is rated Low
Even though extract_function only reads data, uncontrolled read access leaks sensitive information and racks up API costs: an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.
Attacks that exploit this kind of access
The rule that runs extract_function safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Trace, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For extract_function, this is the rule to start with:
extract_function is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Trace, apply this rule, and every extract_function call is checked against it from then on.
Questions about extract_function
Extract a line range out of an enclosing function into a new named helper (AST-aware, TypeScript/JavaScript). Computes the parameter list via free-variable analysis and a return value from bindings used after the slice. The helper is inserted after the enclosing function; the slice becomes a call. Dry-run by default — preview, then re-call with dry_run=false to apply. Returns JSON: { success, edits, extracted_params, return_value, confidence, files_modified }. It is categorised as a Read tool in the Trace MCP Server, which means it retrieves data without modifying state.
Register the Trace MCP server in PolicyLayer and add a rule for extract_function: 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 Trace. Nothing to install.
extract_function 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 extract_function 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 extract_function. 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.
extract_function is provided by the Trace MCP server (nikolai-vysotskyi/trace-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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