updateObservation

THE RISK

Medium Risk

Why updateObservation needs a policy

This tool modifies healthcare data (a FHIR Observation resource) in a healthcare system. While updates are reversible (Write rather than Destructive), the severity is high because: (1) it affects sensitive healthcare records, (2) incorrect updates could compromise patient safety by corrupting critical medical information, and (3) in a healthcare context, data integrity is paramount.

From the tool's definition Tool name 'updateObservation' explicitly performs an update operation. Description states 'Updates an existing observation', which is a reversible modification of data.

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

POLICY

How to control updateObservation

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

policy.json

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

updateObservation 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.

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

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Medplum MCP Server tools

Write createCondition Creates a new condition or diagnosis for a patient. Requires a patient ID and a condition Write createEncounter Creates a new encounter (patient visit). Requires patient ID and status. Write createEpisodeOfCare Creates a new episode of care for a patient. Requires patient ID and status. Write createMedication Creates a new medication resource. Requires medication code or identifier. Write createMedicationRequest Creates a new medication request (prescription). Requires patient ID, medication reference Write createObservation Creates a new observation (lab result, vital sign, etc.). Requires patient ID and code. Write createOrganization Creates a new organization (e.g., hospital, clinic). Requires organization name. Write createPatient Creates a new patient resource. Requires first name, last name, and birth date.

All 37 Medplum MCP Server tools →

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about updateObservation

What does the updateObservation tool do? +

Updates an existing observation. Requires the observation ID and the fields to update. It is categorised as a Write tool in the Medplum MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on updateObservation? +

Register the Medplum MCP Server MCP server in PolicyLayer and add a rule for updateObservation: 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 Medplum MCP Server. Nothing to install.

What risk level is updateObservation? +

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

Can I rate-limit updateObservation? +

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

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

updateObservation is provided by the Medplum MCP Server MCP server (rkirkendall/medplum-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Medplum MCP Server tool call.

Start from Medplum MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →