json_query

THE RISK

High Risk

Why json_query needs a policy

JSONPath queries execute filtering and aggregation logic against JSON data. While this sounds read-like, 'complex filtering and aggregation' implies execution of query expressions whose effects depend on the arguments supplied. On a deprecated PostgreSQL MCP server, JSONPath operations could traverse and expose sensitive nested data structures at scale.

From the tool's definition Complex JSON filtering and aggregation using JSONPath

Documented attack patterns abuse exactly the kind of access json_query gives an agent:

POLICY

How to control json_query

PolicyLayer is an MCP gateway — it sits between your AI agents and Postgres Mcp Legacy, and nothing reaches the server without passing your rules. This is the rule we recommend for json_query:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "json_query": {
      "limits": [
        {
          "counter": "json_query_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

json_query stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

Create a free account and register Postgres Mcp Legacy — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

Execute tools on other servers

Android Forensics ADB MCP Server adb_shell_command EMBA-MCP run_emba_scan Frida Game Hacking MCP remove_breakpoint Procmon request_elevation

Go deeper

High-risk tools in Postgres Mcp Legacy → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about json_query

What does the json_query tool do? +

Complex JSON filtering and aggregation using JSONPath. It is categorised as a Execute tool in the Postgres Mcp Legacy MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on json_query? +

Register the Postgres Mcp Legacy MCP server in PolicyLayer and add a rule for json_query: 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 Postgres Mcp Legacy. Nothing to install.

What risk level is json_query? +

json_query is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit json_query? +

Yes. Add a rate_limit block to the json_query 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.

How do I block json_query completely? +

Set action: deny in the PolicyLayer policy for json_query. 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.

What MCP server provides json_query? +

json_query is provided by the Postgres Mcp Legacy MCP server (neverinfamous/postgres-mcp-legacy). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Postgres Mcp Legacy tool call.

Start from Postgres Mcp Legacy, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →