// MCP TOOL REFERENCE

proxy_set_ja3_spoof

Legacy: enable fingerprint spoofing (deprecated, use proxy_set_fingerprint_spoof with a preset). The ja3 parameter is accepted but ignored — the default Chrome preset is used.

ServerProxy
CategoryExecute

How to control proxy_set_ja3_spoof ↓

WHAT IT DOES

What proxy_set_ja3_spoof does on Proxy

AI agents invoke proxy_set_ja3_spoof to trigger actions in Proxy. 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.

THE RISK

High Risk

Why proxy_set_ja3_spoof needs a policy

This tool activates TLS/JA3 fingerprint spoofing on the MITM proxy, causing it to impersonate a different TLS client profile (Chrome preset) for outbound connections. This is an external operation with real network-level effects (manipulating TLS handshakes), making it Execute.

From the tool's definition enable fingerprint spoofing — triggers TLS fingerprint spoofing behavior on the proxy, affecting outbound network connections

Documented attack patterns abuse exactly the kind of access proxy_set_ja3_spoof gives an agent:

POLICY

How to control proxy_set_ja3_spoof

PolicyLayer is an MCP gateway — it sits between your AI agents and Proxy, and nothing reaches the server without passing your rules. This is the rule we recommend for proxy_set_ja3_spoof:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "proxy_set_ja3_spoof": {
      "limits": [
        {
          "counter": "proxy_set_ja3_spoof_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

proxy_set_ja3_spoof 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.

Create a free account and register Proxy — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Proxy tools

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All 89 Proxy tools →

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Go deeper

High-risk tools in Proxy → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about proxy_set_ja3_spoof

What does the proxy_set_ja3_spoof tool do? +

Legacy: enable fingerprint spoofing (deprecated, use proxy_set_fingerprint_spoof with a preset). The ja3 parameter is accepted but ignored — the default Chrome preset is used. It is categorised as a Execute tool in the Proxy MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on proxy_set_ja3_spoof? +

Register the Proxy MCP server in PolicyLayer and add a rule for proxy_set_ja3_spoof: 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 Proxy. Nothing to install.

What risk level is proxy_set_ja3_spoof? +

proxy_set_ja3_spoof is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit proxy_set_ja3_spoof? +

Yes. Add a rate_limit block to the proxy_set_ja3_spoof 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 proxy_set_ja3_spoof completely? +

Set action: deny in the PolicyLayer policy for proxy_set_ja3_spoof. 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 proxy_set_ja3_spoof? +

proxy_set_ja3_spoof is provided by the Proxy MCP server (yfe404/proxy-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Proxy tool call.

Start from Proxy, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →

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89 Proxy tools catalogued and risk-classified — across an index of 43,000+ MCP servers.