update_memory · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What update_memory does on Nexus Core

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

WHY IT NEEDS A POLICY

Why update_memory needs a policy

This tool creates or modifies data (memory state) in a reversible manner—the modification can be undone by updating the memory again to a previous value. It does not delete data (Destructive), execute arbitrary code (Execute), move money (Financial), or retrieve data read-only (Read).

From the tool's definition Tool description states 'Modify the value of an existing memory', which is a data modification operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_memory Rate-limited

update_memory 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": {
    "update_memory": {
      "limits": [
        {
          "counter": "update_memory_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about update_memory

What does the update_memory tool do? +

Modify the value of an existing memory. Returns not_found if key absent. It is categorised as a Write tool in the Nexus Core MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_memory? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for update_memory: 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 Nexus Core. Nothing to install.

What risk level is update_memory? +

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

Can I rate-limit update_memory? +

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

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

update_memory is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.