substack_post_note · Substack MCP Server MCP: Risk & Policy

WHAT IT DOES

What substack_post_note does on Substack MCP Server

AI agents use substack_post_note to create or update resources in Substack MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Substack MCP Server environment.

WHY IT NEEDS A POLICY

Why substack_post_note needs a policy

This tool creates new content on Substack Notes (a public social feature) in a reversible manner—posted notes can be edited or deleted after publication. This is a Write operation (creates/modifies data reversibly) rather than Execute or Destructive, as it doesn't run arbitrary code or permanently delete content.

From the tool's definition Tool description states it will 'Post a short note', and the server description indicates it 'support[s] specialized features like...posting to Substack Notes'.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

substack_post_note Rate-limited

substack_post_note 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "substack_post_note": {
      "limits": [
        {
          "counter": "substack_post_note_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Substack MCP Server, so you can run agents against it safely.

FAQ

Questions about substack_post_note

What does the substack_post_note tool do? +

Post a short note (like a tweet). It is categorised as a Write tool in the Substack MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on substack_post_note? +

Register the Substack MCP Server MCP server in PolicyLayer and add a rule for substack_post_note: 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 Server. Nothing to install.

What risk level is substack_post_note? +

substack_post_note is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit substack_post_note? +

Yes. Add a rate_limit block to the substack_post_note 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 substack_post_note completely? +

Set action: deny in the PolicyLayer policy for substack_post_note. 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 substack_post_note? +

substack_post_note is provided by the Substack MCP Server MCP server (jessicaruthabbott/my-substack-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.