substack_add_image · Substack MCP Server MCP: Risk & Policy

WHAT IT DOES

What substack_add_image does on Substack MCP Server

AI agents use substack_add_image 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_add_image needs a policy

Adding an image to a draft is a content modification operation that can be undone (the image can be removed or the draft deleted). It does not execute arbitrary code, delete data irreversibly, or commit financial transactions. While it could be misused to insert inappropriate images into a draft intended for publication, the impact is limited to draft state and reversible.

From the tool's definition Tool description states 'Add an image to a draft' — this modifies draft content by inserting an image, a reversible operation. Server description confirms the tool is part of capabilities for 'creating drafts, publishing posts, and uploading images.'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

substack_add_image Rate-limited

substack_add_image 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_add_image": {
      "limits": [
        {
          "counter": "substack_add_image_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_add_image

What does the substack_add_image tool do? +

Add an image to a draft. 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_add_image? +

Register the Substack MCP Server MCP server in PolicyLayer and add a rule for substack_add_image: 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_add_image? +

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

Can I rate-limit substack_add_image? +

Yes. Add a rate_limit block to the substack_add_image 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_add_image completely? +

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

substack_add_image 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.