AI agents use update_draft to create or update resources in Substack — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Substack environment.
'update_draft' creates or modifies data reversibly (a draft can be edited multiple times and is not final until published). This is a Write operation. It is not Destructive (drafts remain recoverable), not Execute (no arbitrary code/command triggering), not Financial. Severity is medium because misuse could alter unpublished content, but the changes are reversible and limited to draft scope.
From the tool's definition Tool name 'update_draft' and sibling context show this modifies existing draft posts on Substack. The server description states the MCP enables 'create drafts' and related operations, and 'update_draft' fits the reversible modification pattern alongside…
Documented attack patterns abuse exactly the kind of access update_draft gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Substack, and nothing reaches the server without passing your rules. This is the rule we recommend for update_draft:
{
"version": "1",
"default": "deny",
"tools": {
"update_draft": {
"limits": [
{
"counter": "update_draft_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update_draft 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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update_draft. It is categorised as a Write tool in the Substack MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Substack MCP server in PolicyLayer and add a rule for update_draft: 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. Nothing to install.
update_draft 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 update_draft 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 update_draft. 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.
update_draft is provided by the Substack MCP server (nanameru/substack-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Substack, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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11 Substack tools catalogued and risk-classified — across an index of 43,000+ MCP servers.