// MCP TOOL REFERENCE

merge_entities

Merge multiple entities into one. Moves all observations, embeddings, and relationships from source entities to target, then deletes sources. Use after consolidate mode:

ServerHippocampus
CategoryDestructive

How to control merge_entities ↓

WHAT IT DOES

What merge_entities does on Hippocampus

AI agents call merge_entities to permanently remove resources in Hippocampus — typically in cleanup and lifecycle workflows. It does its job in a single call, and there is no undo.

THE RISK

Critical Risk

Why merge_entities needs a policy

While the merge operation also involves writing (moving data to the target), the defining and most severe aspect is that source entities are deleted after the merge. This deletion is irreversible — the original discrete entities cease to exist. Per the severity rules, Destructive outranks Write.

From the tool's definition 'then deletes sources' — source entities are permanently removed after merge; this is an irreversible deletion of entities, observations, embeddings, and relationships

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

POLICY

How to control merge_entities

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

policy.json

{
  "version": "1",
  "default": "deny",
  "hide": [
    "merge_entities"
  ]
}

merge_entities disappears from the agent's tool list entirely, and any attempt to call it is denied. The rest of the server keeps working.

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

RESTRICT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Hippocampus tools

Destructive forget Delete a specific memory or an entire entity and all its associated data. Use with care — Write merge Merge multiple observations into one. Atomic operation: provide merged text + list of obse Write onboard Bootstrap memory from the current AI session. Returns extraction instructions — follow the Write remember Store a memory or piece of information. Use this to save facts, preferences, decisions, re Write update Replace an existing observation with new content. Finds the old observation by exact conte Read check_version Check if cached entity content is still current. Pass a previously received version_hash t Read context Get full context about a topic: the entity, its observations, relationships, and related e Read recall Search memories by semantic similarity and keyword match. Returns relevant stored informat

All 11 Hippocampus tools →

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Go deeper

Critical-risk tools in Hippocampus → Every critical-risk tool this server exposes, in one view.
All critical-risk MCP tools → Every critical-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Blast radius → How much damage one compromised or confused agent can do — and how to bound it.
Tool call approval → Approval gates on individual tool calls: auto-allow, prompt, or deny.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about merge_entities

What does the merge_entities tool do? +

Merge multiple entities into one. Moves all observations, embeddings, and relationships from source entities to target, then deletes sources. Use after consolidate mode:. It is categorised as a Destructive tool in the Hippocampus MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.

How do I enforce a policy on merge_entities? +

Register the Hippocampus 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 Hippocampus. Nothing to install.

What risk level is merge_entities? +

merge_entities is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.

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 Hippocampus MCP server (karrolcia/hippocampus). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Hippocampus tool call.

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

CHECK YOUR STACK →

Free to start. No card required.

11 Hippocampus tools catalogued and risk-classified — across an index of 43,000+ MCP servers.