set_frontmatter

THE RISK

Medium Risk

Why set_frontmatter needs a policy

The tool creates or modifies frontmatter and CSS styling within Marp presentation projects. This is reversible—frontmatter and styles can be edited, reverted, or reset without permanent data loss. It does not delete data (thus not Destructive), does not execute arbitrary code or external operations (thus not Execute), and does not involve financial transactions (thus not Financial). This is clearly a Write operation.

From the tool's definition Tool description states 'Initialize or update required Marp frontmatter' and 'inject active style CSS', indicating modification of presentation configuration and styling files.

Documented attack patterns abuse exactly the kind of access set_frontmatter gives an agent:

POLICY

How to control set_frontmatter

PolicyLayer is an MCP gateway — it sits between your AI agents and Marp MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for set_frontmatter:

policy.json

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

set_frontmatter 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.

Create a free account and register Marp MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Marp MCP Server tools

Write add_image_transition Insert a full-screen background image slide immediately before the specified slide to crea Write batch_manage_slides Apply multiple slide operations (insert/replace/delete/move) to a Marp file in a single fi Write create_presentation Create a new Marp presentation file in one step — initializes frontmatter, adds a title sl Write export_slide Export a Marp markdown presentation to HTML, PDF, or PPTX using marp-cli. Write generate_agenda Auto-generate an agenda slide from section slides (detected by CSS class) and insert it be Write generate_slide_ids Assign stable UUID slide IDs to every slide in a Marp file. Write manage_slide Insert, replace, or delete slides in a Marp file using slide IDs. Read list_layouts List all available slide layouts with their required/optional parameters.

All 11 Marp MCP Server tools →

Write tools on other servers

M-Team MCP Server download_torrent YouTube MCP Server generate_video_title Android Forensics ADB MCP Server combine_reports 0xarchive web3_signup

Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about set_frontmatter

What does the set_frontmatter tool do? +

Initialize or update required Marp frontmatter (marp:true, theme, header, paginate) and inject active style CSS. It is categorised as a Write tool in the Marp 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 set_frontmatter? +

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

What risk level is set_frontmatter? +

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

Can I rate-limit set_frontmatter? +

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

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

set_frontmatter is provided by the Marp MCP Server MCP server (masaki39/marp-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Marp MCP Server tool call.

Start from Marp MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →