AI agents use list_insert_before to create or update resources in Prometheus MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Prometheus MCP Server environment.
The tool inserts a value into a list at a specific position (before a pivot), which is a data modification operation. This is reversible (the item can be removed), placing it in the Write category. The server context (Prometheus/AWS) is somewhat incongruent with a list insertion operation, which lowers confidence slightly, but the description clearly describes a write/modify action.
From the tool's definition Insert value before pivot in list
Documented attack patterns abuse exactly the kind of access list_insert_before gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Prometheus MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_insert_before:
{
"version": "1",
"default": "deny",
"tools": {
"list_insert_before": {
"limits": [
{
"counter": "list_insert_before_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}list_insert_before 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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Insert value before pivot in list. It is categorised as a Write tool in the Prometheus MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Prometheus MCP Server MCP server in PolicyLayer and add a rule for list_insert_before: 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 Prometheus MCP Server. Nothing to install.
list_insert_before 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 list_insert_before 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 list_insert_before. 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.
list_insert_before is provided by the Prometheus MCP Server MCP server (awslabs.prometheus-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Prometheus MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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805 Prometheus MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.