prepend_to_page · Silverbullet MCP: Risk & Policy

WHAT IT DOES

What prepend_to_page does on Silverbullet

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

WHY IT NEEDS A POLICY

Why prepend_to_page needs a policy

This tool creates or modifies data reversibly by prepending content to a page. It does not delete, execute code, trigger external operations, or move money. While it modifies state, the changes are not irreversible. Severity is medium because an agent could spam prepend operations or corrupt page structure, but the OAuth 2.1 and collision-safe write mechanisms mentioned in the server description mitigate some risks.

From the tool's definition Tool name 'prepend_to_page' and description 'Insert content at the top of an existing page' indicate modification of existing data. The operation is reversible—content can be edited or removed—distinguishing it from destructive operations like delete_page.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

prepend_to_page Rate-limited

prepend_to_page 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": {
    "prepend_to_page": {
      "limits": [
        {
          "counter": "prepend_to_page_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 Silverbullet, so you can run agents against it safely.

FAQ

Questions about prepend_to_page

What does the prepend_to_page tool do? +

Insert content at the top of an existing page. By default, inserts after YAML frontmatter if present (so frontmatter stays at byte 0); set position to \. It is categorised as a Write tool in the Silverbullet MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on prepend_to_page? +

Register the Silverbullet MCP server in PolicyLayer and add a rule for prepend_to_page: 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 Silverbullet. Nothing to install.

What risk level is prepend_to_page? +

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

Can I rate-limit prepend_to_page? +

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

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

prepend_to_page is provided by the Silverbullet MCP server (xmatthewx/silverbullet-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.