AI agents use merge to create or update resources in Surreal — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Surreal environment.
In database contexts, 'merge' typically performs an upsert-like operation—combining insert and update logic to create or modify records. This is a reversible write operation. Given the empty description and database context, this is classified as Write rather than Execute. Severity is high because a merge operation on a database can affect multiple records and modify data structure.
From the tool's definition Tool named 'merge' on a SurrealDB MCP server; sibling tools include 'create', 'update', 'patch', 'insert', 'upsert' which are all write operations. The tool description is empty, limiting direct evidence.
Documented attack patterns abuse exactly the kind of access merge gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Surreal, and nothing reaches the server without passing your rules. This is the rule we recommend for merge:
{
"version": "1",
"default": "deny",
"tools": {
"merge": {
"limits": [
{
"counter": "merge_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}merge 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.
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merge. It is categorised as a Write tool in the Surreal MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Surreal MCP server in PolicyLayer and add a rule for merge: 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 Surreal. Nothing to install.
merge is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the merge 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.
Set action: deny in the PolicyLayer policy for merge. 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.
merge is provided by the Surreal MCP server (lfnovo/surreal-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Surreal, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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10 Surreal tools catalogued and risk-classified — across an index of 43,000+ MCP servers.