Extract specific fields from JSON content in a flow using JSONPath expressions
AI agents call extract_json_fields to retrieve information from mitmproxy-mcp MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves and filters JSON data from existing flow content using JSONPath queries. It performs no side effects, does not modify or delete data, does not execute code or commands, and does not involve financial transactions. The operation is read-only introspection of existing data, making it a Read category tool with low severity risk.
From the tool's definition Tool description states it 'Extract[s] specific fields from JSON content in a flow using JSONPath expressions' — a pure data retrieval operation with no modification, deletion, or execution of external commands.
Documented attack patterns abuse exactly the kind of access extract_json_fields gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and mitmproxy-mcp MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for extract_json_fields:
{
"version": "1",
"default": "deny",
"tools": {
"extract_json_fields": {}
}
}extract_json_fields is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Extract specific fields from JSON content in a flow using JSONPath expressions. It is categorised as a Read tool in the mitmproxy-mcp MCP Server MCP Server, which means it retrieves data without modifying state.
Register the mitmproxy-mcp MCP Server MCP server in PolicyLayer and add a rule for extract_json_fields: 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 mitmproxy-mcp MCP Server. Nothing to install.
extract_json_fields 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_json_fields 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_json_fields. 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_json_fields is provided by the mitmproxy-mcp MCP Server MCP server (lucasoeth/mitmproxy-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from mitmproxy-mcp 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.
4 mitmproxy-mcp MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.