Create a copy of an existing post as a new draft. Perfect for using posts as templates. IMPORTANT: You MUST ALWAYS ask the user to confirm duplication in a follow-up message BEFORE calling this tool with confirm_duplicate=true. Never set confirm_duplicate=true on the first request, even if the us...
AI agents use duplicate_post to create or update resources in Substack Mcp Plus — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Substack Mcp Plus environment.
This tool creates new content (a duplicate draft) in the user's Substack account. While this is reversible and does not permanently alter existing posts, it does modify the user's content library and could be misused to spam or create unwanted duplicates.
From the tool's definition Tool creates a copy of an existing post as a new draft, which represents creating new data in the Substack system.
Documented attack patterns abuse exactly the kind of access duplicate_post gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Substack Mcp Plus, and nothing reaches the server without passing your rules. This is the rule we recommend for duplicate_post:
{
"version": "1",
"default": "deny",
"tools": {
"duplicate_post": {
"limits": [
{
"counter": "duplicate_post_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}duplicate_post 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 a copy of an existing post as a new draft. Perfect for using posts as templates. IMPORTANT: You MUST ALWAYS ask the user to confirm duplication in a follow-up message BEFORE calling this tool with confirm_duplicate=true. Never set confirm_duplicate=true on the first request, even if the user explicitly asks to duplicate. It is categorised as a Write tool in the Substack Mcp Plus MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Substack Mcp Plus MCP server in PolicyLayer and add a rule for duplicate_post: 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 Substack Mcp Plus. Nothing to install.
duplicate_post 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 duplicate_post 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 duplicate_post. 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.
duplicate_post is provided by the Substack Mcp Plus MCP server (ty13r/substack-mcp-plus). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Substack Mcp Plus, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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