juno_functions_build · Junobuild MCP: Risk & Policy

WHAT IT DOES

What juno_functions_build does on Junobuild

AI agents invoke juno_functions_build to trigger actions in Junobuild. 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 juno_functions_build needs a policy

Building serverless functions involves executing build scripts, transpilation, and code transformation processes. While this is not arbitrary code execution in the user's local environment, it invokes external build systems and compilers whose behavior depends on the function code provided as input.

From the tool's definition Tool description states it 'Build[s] your serverless functions' and supports compilation for Rust, TypeScript, and JavaScript. Building functions triggers compilation and code execution in a controlled environment.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

juno_functions_build Rate-limited

juno_functions_build 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": {
    "juno_functions_build": {
      "limits": [
        {
          "counter": "juno_functions_build_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 Junobuild, so you can run agents against it safely.

FAQ

Questions about juno_functions_build

What does the juno_functions_build tool do? +

Build your serverless functions. Supports Rust, TypeScript, and JavaScript. The CLI auto-detects the language if not specified. It is categorised as a Execute tool in the Junobuild MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on juno_functions_build? +

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

What risk level is juno_functions_build? +

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

Can I rate-limit juno_functions_build? +

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

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

juno_functions_build is provided by the Junobuild MCP server (junobuild-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.