preview_fix · Supabase Security MCP: Risk & Policy

WHAT IT DOES

What preview_fix does on Supabase Security

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

WHY IT NEEDS A POLICY

Why preview_fix needs a policy

An AI agent can call preview_fix faster than any human can review — one bad instruction and it creates or modifies resources in Supabase Security by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

preview_fix Rate-limited

preview_fix 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": {
    "preview_fix": {
      "limits": [
        {
          "counter": "preview_fix_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 Supabase Security, so you can run agents against it safely.

FAQ

Questions about preview_fix

What does the preview_fix tool do? +

Preview what a fix would change WITHOUT applying it. Wraps the fix SQL in BEGIN; ... ROLLBACK; and returns what would have happened. Safe to call for any finding. It is categorised as a Write tool in the Supabase Security MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on preview_fix? +

Register the Supabase Security MCP server in PolicyLayer and add a rule for preview_fix: 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 Supabase Security. Nothing to install.

What risk level is preview_fix? +

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

Can I rate-limit preview_fix? +

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

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

preview_fix is provided by the Supabase Security MCP server (perufitlife/supabase-security-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.