approve_write · Fhir Synthetic MCP: Risk & Policy

WHAT IT DOES

What approve_write does on Fhir Synthetic

AI agents use approve_write to create or update resources in Fhir Synthetic — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Fhir Synthetic environment.

WHY IT NEEDS A POLICY

Why approve_write needs a policy

This tool commits a previously proposed write operation (from propose_observation) after human approval. While the human-in-the-loop gate mitigates risk by requiring explicit approval, the tool itself performs an irreversible state change to the FHIR data system. The structured audit logging further reduces severity from high to medium.

From the tool's definition Tool name is 'approve_write' and description states 'Commit a staged write', indicating it finalizes and applies a write operation to the system.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

approve_write Rate-limited

approve_write stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "approve_write": {
      "limits": [
        {
          "counter": "approve_write_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Fhir Synthetic, so you can run agents against it safely.

FAQ

Questions about approve_write

What does the approve_write tool do? +

HUMAN-IN-THE-LOOP GATE. Commit a staged write. It is categorised as a Write tool in the Fhir Synthetic MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on approve_write? +

Register the Fhir Synthetic MCP server in PolicyLayer and add a rule for approve_write: 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 Fhir Synthetic. Nothing to install.

What risk level is approve_write? +

approve_write is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit approve_write? +

Yes. Add a rate_limit block to the approve_write 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 approve_write completely? +

Set action: deny in the PolicyLayer policy for approve_write. 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 approve_write? +

approve_write is provided by the Fhir Synthetic MCP server (krishnakakani-github/fhir-synthetic-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.