open_uri · Espresso MCP: Risk & Policy

WHAT IT DOES

What open_uri does on Espresso

AI agents invoke open_uri to trigger actions in Espresso. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why open_uri needs a policy

Opening a URI on a device triggers an external action (launching apps, intents, URLs, deep links) whose effects depend entirely on the URI provided. A malicious or unexpected URI could launch sensitive apps, initiate phone calls (tel:), send SMS (sms:), open browser to phishing sites, or trigger deep-link actions in installed apps.

From the tool's definition 'Open a URI on the connected Android device' — triggers an external operation on a real device by launching an arbitrary URI

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

open_uri Rate-limited

open_uri 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.

View as policy code

policy.json

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

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about open_uri

What does the open_uri tool do? +

Open a URI on the connected Android device. It is categorised as a Execute tool in the Espresso MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on open_uri? +

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

What risk level is open_uri? +

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

Can I rate-limit open_uri? +

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

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

open_uri is provided by the Espresso MCP server (vs4vijay/espresso-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.