start_session

THE RISK

High Risk

This tool triggers an external operation (starting a browser process and opening an editor interface). While the operation itself is not inherently harmful and does not modify data, it executes a command whose side effects are not fully reversible or under direct control.

From the tool's definition Tool description states it will 'Start browser preview and open Excalidraw editor interface' — this involves launching an external operation (browser process) whose effects depend on context.

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

HOW TO CONTROL START_SESSION

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "start_session": {
      "limits": [
        {
          "counter": "start_session_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

start_session stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

Create a free account and register Excalidraw 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.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

More Excalidraw MCP Server tools

Destructive delete_diagram Delete the specified diagram session.\n\n Destructive delete_element Delete a specific element from the canvas.\n\n Write add_elements Add multiple Excalidraw elements to the canvas.\n\n Write add_template_architecture Add a built-in architecture diagram template to the canvas.\n\n Write create_diagram Create a new diagram or clear an existing session.\n\n Write create_from_mermaid Create diagram elements from Mermaid syntax.\n\n Write export_diagram Export the current diagram to a PNG, SVG, or JSON file.\n\n Write update_element Update attributes of an existing element.\n\n

All 11 Excalidraw MCP Server tools →

Execute tools on other servers

Frida Game Hacking MCP remove_breakpoint Procmon request_elevation WireMCP capture_packets Pentest Ai run_probe

Go deeper

High-risk tools in Excalidraw MCP Server → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

What does the start_session tool do? +

Start browser preview and open Excalidraw editor interface.\n\n. It is categorised as a Execute tool in the Excalidraw MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on start_session? +

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

What risk level is start_session? +

start_session is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit start_session? +

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

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

start_session is provided by the Excalidraw MCP Server MCP server (scofieldfree/excalidraw-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Excalidraw MCP Server tool call.

Deterministic rules across all 11 Excalidraw MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.

GOVERN EXCALIDRAW →

Free to start. No card required.

11 Excalidraw MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.

// WHAT START_SESSION ON EXCALIDRAW MCP SERVER DOES

// THE RISK

// HOW TO CONTROL START_SESSION

// EXPLORE