merge_entities · Lightrag MCP: Risk & Policy

WHAT IT DOES

What merge_entities does on Lightrag

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

WHY IT NEEDS A POLICY

Why merge_entities needs a policy

The merge_entities tool creates a modified state by consolidating entities and their relationships. While relationships are preserved (suggesting reversibility in principle), the operation fundamentally rewrites entity records and their interconnections in the knowledge graph. This is more severe than a simple Read operation but does not permanently destroy data or prevent undo (it's not Destructive).

From the tool's definition Tool performs merge operation on entities, which modifies data structure by combining multiple entities into one while 'preserving all relationships'. This is a reversible structural transformation that alters the graph data model.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

merge_entities Rate-limited

merge_entities 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": {
    "merge_entities": {
      "limits": [
        {
          "counter": "merge_entities_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

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

FAQ

Questions about merge_entities

What does the merge_entities tool do? +

Merge multiple entities into a single entity, preserving all relationships. It is categorised as a Write tool in the Lightrag MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on merge_entities? +

Register the Lightrag MCP server in PolicyLayer and add a rule for merge_entities: 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 Lightrag. Nothing to install.

What risk level is merge_entities? +

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

Can I rate-limit merge_entities? +

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

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

merge_entities is provided by the Lightrag MCP server (lightrag-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.