canvas_send_message · Canvas MCP: Risk & Policy

WHAT IT DOES

What canvas_send_message does on Canvas

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

WHY IT NEEDS A POLICY

Why canvas_send_message needs a policy

This tool creates new data (messages) in Canvas, making it a Write operation. Severity is medium because misuse could result in spam, harassment, or unwanted communications to students/instructors, but with limited blast radius compared to destructive or financial actions. The dry-run safety mechanism mentioned in the server description provides some mitigation.

From the tool's definition Tool description states 'Send a Canvas Conversations (inbox) message to one or more people,' which creates new communication data in the LMS.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

canvas_send_message Rate-limited

canvas_send_message 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": {
    "canvas_send_message": {
      "limits": [
        {
          "counter": "canvas_send_message_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 Canvas, so you can run agents against it safely.

FAQ

Questions about canvas_send_message

What does the canvas_send_message tool do? +

Send a Canvas Conversations (inbox) message to one or more people. Resolve recipient_ids with. It is categorised as a Write tool in the Canvas MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on canvas_send_message? +

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

What risk level is canvas_send_message? +

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

Can I rate-limit canvas_send_message? +

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

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

canvas_send_message is provided by the Canvas MCP server (tylergibbs1/canvas-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.