crystal_update

THE RISK

Medium Risk

Why crystal_update needs a policy

The tool modifies existing data (memories) reversibly without deleting or destroying it. This is a Write operation rather than Destructive since updates can be reversed by further updates.

From the tool's definition Tool description states 'Update an existing Memory Crystal memory in place' and 'Use to correct or enrich a memory', indicating modification of stored data.

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

POLICY

How to control crystal_update

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

policy.json

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

crystal_update 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 Memory Crystal 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 Memory Crystal MCP Server tools

Destructive crystal_forget Archive or permanently delete a memory. Use archive (permanent=false, the default) to soft Write crystal_capture Capture a memory into Memory Crystal Write crystal_idea_action Take action on a memory discovery -- star it as valuable, dismiss it, or mark it as read. Write crystal_supersede Atomically replace a stale or incorrect memory with a successor. The old memory is archive Write crystal_checkpoint Create a manual Memory Checkpoint only when the user explicitly asks for a checkpoint or b Write crystal_create_knowledge_base Create a Memory Crystal knowledge base. Write crystal_edit Update an existing memory in Memory Crystal. Use to correct errors, add new information, o Write crystal_import_knowledge Import text chunks into a Memory Crystal knowledge base.

All 31 Memory Crystal MCP Server tools →

Write tools on other servers

M-Team MCP Server download_torrent YouTube MCP Server generate_video_title Android Forensics ADB MCP Server combine_reports 0xarchive web3_signup

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 crystal_update

What does the crystal_update tool do? +

Update an existing Memory Crystal memory in place. Use to correct or enrich a memory when it remains the same fact, preference, rule, or decision. It is categorised as a Write tool in the Memory Crystal 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 crystal_update? +

Register the Memory Crystal MCP Server MCP server in PolicyLayer and add a rule for crystal_update: 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 Memory Crystal MCP Server. Nothing to install.

What risk level is crystal_update? +

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

Can I rate-limit crystal_update? +

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

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

crystal_update is provided by the Memory Crystal MCP Server MCP server (memorycrystal/memorycrystal). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Memory Crystal MCP Server tool call.

Start from Memory Crystal 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 →