supabase_create_signed_url · Supabase MCP Server MCP

WHAT IT DOES

What supabase_create_signed_url does on Supabase MCP Server

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

WHY IT NEEDS A POLICY

Why supabase_create_signed_url needs a policy

Creating a signed URL is a reversible write operation that generates a new access credential/token for a resource. While it doesn't modify the underlying file itself, it creates a new temporary access mechanism. This is classified as Write rather than Read because it generates a new artifact (the signed URL) that has authentication/authorization implications.

From the tool's definition Tool name is 'supabase_create_signed_url' and description states it 'Create[s] a temporary signed URL for private files'. The action creates a new signed URL resource, which is a data modification (generating and storing/returning a new signed URL token).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

supabase_create_signed_url Rate-limited

supabase_create_signed_url 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": {
    "supabase_create_signed_url": {
      "limits": [
        {
          "counter": "supabase_create_signed_url_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Supabase MCP Server, so you can run agents against it safely.

FAQ

Questions about supabase_create_signed_url

What does the supabase_create_signed_url tool do? +

Create a temporary signed URL for private files. It is categorised as a Write tool in the Supabase 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 supabase_create_signed_url? +

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

What risk level is supabase_create_signed_url? +

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

Can I rate-limit supabase_create_signed_url? +

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

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

supabase_create_signed_url is provided by the Supabase MCP Server MCP server (sweir1/supabase-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.