Create one or more indexes on a MongoDB collection
AI agents use createIndex to create or update resources in MongoDB — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MongoDB environment.
Creating indexes is a schema modification that changes the database state reversibly (indexes can be dropped). While it doesn't create or delete data directly, it materially alters the collection's structure and performance characteristics. This is a Write operation because the change can be undone (indexes can be removed).
From the tool's definition Tool name 'createIndex' and description 'Create one or more indexes on a MongoDB collection' indicate this modifies database schema by creating indexes, which is a reversible write operation.
Documented attack patterns abuse exactly the kind of access createIndex gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MongoDB, and nothing reaches the server without passing your rules. This is the rule we recommend for createIndex:
{
"version": "1",
"default": "deny",
"tools": {
"createIndex": {
"limits": [
{
"counter": "createindex_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}createIndex 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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Create one or more indexes on a MongoDB collection. It is categorised as a Write tool in the MongoDB MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the MongoDB MCP server in PolicyLayer and add a rule for createIndex: 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 MongoDB. Nothing to install.
createIndex 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 createIndex 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 createIndex. 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.
createIndex is provided by the MongoDB MCP server (kiliczsh/mcp-mongo-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from MongoDB, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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