verify_postcondition · Musubix MCP: Risk & Policy

WHAT IT DOES

What verify_postcondition does on Musubix

AI agents invoke verify_postcondition to trigger actions in Musubix. 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 verify_postcondition needs a policy

This tool runs formal verification by invoking the Z3 SMT solver to evaluate logical conditions. It executes external solver processes whose results depend on the supplied precondition, command, and postcondition arguments. No data is written or deleted, but it triggers external computation (SMT solving), placing it in the Execute category.

From the tool's definition 'Verify a Hoare triple {P} C {Q} using Z3 SMT solver' and 'Checks if the postcondition Q holds after executing C'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

verify_postcondition Rate-limited

verify_postcondition 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": {
    "verify_postcondition": {
      "limits": [
        {
          "counter": "verify_postcondition_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 Musubix, so you can run agents against it safely.

FAQ

Questions about verify_postcondition

What does the verify_postcondition tool do? +

Verify a Hoare triple {P} C {Q} using Z3 SMT solver. Checks if the postcondition Q holds after executing C when precondition P is satisfied. It is categorised as a Execute tool in the Musubix MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on verify_postcondition? +

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

What risk level is verify_postcondition? +

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

Can I rate-limit verify_postcondition? +

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

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

verify_postcondition is provided by the Musubix MCP server (@nahisaho/musubix-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.