testkit_last_failure · Yaver MCP: Risk & Policy

WHAT IT DOES

What testkit_last_failure does on Yaver

AI agents invoke testkit_last_failure to trigger actions in Yaver. 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.

PARAMETERS

Parameter	Type	Required	Description
`root`	string	—	Spec root (default: yaver-tests)

Parameters from the server's own tool schema.

WHY IT NEEDS A POLICY

Why testkit_last_failure needs a policy

testkit_last_failure triggers real processes with real consequences. An agent gone sideways doesn't fire it once — it starts dozens of builds, sends mass notifications, or burns through compute before anyone looks up.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

testkit_last_failure Rate-limited

testkit_last_failure 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": {
    "testkit_last_failure": {
      "limits": [
        {
          "counter": "testkit_last_failure_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 Yaver, so you can run agents against it safely.

FAQ

Questions about testkit_last_failure

What does the testkit_last_failure tool do? +

Read the most recent failed run from local history. Returns the spec name, the failing step, the screenshot path, and the error — exactly what an AI agent needs to propose a patch. It is categorised as a Execute tool in the Yaver MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

What parameters does testkit_last_failure accept? +

testkit_last_failure accepts 1 parameter: root. The full parameter table on this page comes from the server's own tool schema.

How do I enforce a policy on testkit_last_failure? +

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

What risk level is testkit_last_failure? +

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

Can I rate-limit testkit_last_failure? +

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

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

testkit_last_failure is provided by the Yaver MCP server (yaver-cli). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.