har_playback · MCP Playwright Server MCP: Risk & Policy

WHAT IT DOES

What har_playback does on MCP Playwright Server

AI agents invoke har_playback to trigger actions in MCP Playwright Server. 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 har_playback needs a policy

This tool intercepts and mocks network responses during browser automation by loading a HAR file. It actively modifies the browser's network behavior, causing it to return recorded responses instead of real ones. This is an Execute-level action as it triggers external browser operations and alters runtime behavior.

From the tool's definition 'Use a HAR file to mock network responses. Requests matching the HAR will return recorded responses.'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

har_playback Rate-limited

har_playback 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": {
    "har_playback": {
      "limits": [
        {
          "counter": "har_playback_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 MCP Playwright Server, so you can run agents against it safely.

FAQ

Questions about har_playback

What does the har_playback tool do? +

Use a HAR file to mock network responses. Requests matching the HAR will return recorded responses. It is categorised as a Execute tool in the MCP Playwright Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on har_playback? +

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

What risk level is har_playback? +

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

Can I rate-limit har_playback? +

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

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

har_playback is provided by the MCP Playwright Server MCP server (j0hanz/playwright-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.