send_private_transaction

THE RISK

High Risk

Why send_private_transaction needs a policy

This tool sends blockchain transactions, which constitutes executing external operations with potentially irreversible on-chain effects. While it uses Flashbots Protect to avoid MEV, it still triggers real transactions on Arbitrum or BNB Chain. The severity is critical because a misused transaction could drain funds, interact with malicious contracts, or cause significant financial harm.

From the tool's definition Send a transaction via Flashbots Protect RPC to avoid MEV extraction (frontrunning, sandwich attacks)

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

POLICY

How to control send_private_transaction

PolicyLayer is an MCP gateway — it sits between your AI agents and Sperax Ecosystem Crypto & DeFI MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for send_private_transaction:

policy.json

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

send_private_transaction 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 Sperax Ecosystem Crypto & DeFI MCP Server — 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 →

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EXPLORE

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Go deeper

High-risk tools in Sperax Ecosystem Crypto & DeFI MCP Server → 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 send_private_transaction

What does the send_private_transaction tool do? +

Send a transaction via Flashbots Protect RPC to avoid MEV extraction (frontrunning, sandwich attacks). It is categorised as a Execute tool in the Sperax Ecosystem Crypto & DeFI MCP 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 send_private_transaction? +

Register the Sperax Ecosystem Crypto & DeFI MCP Server MCP server in PolicyLayer and add a rule for send_private_transaction: 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 Sperax Ecosystem Crypto & DeFI MCP Server. Nothing to install.

What risk level is send_private_transaction? +

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

Can I rate-limit send_private_transaction? +

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

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

send_private_transaction is provided by the Sperax Ecosystem Crypto & DeFI MCP Server MCP server (sperax/sperax-crypto-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Sperax Ecosystem Crypto & DeFI MCP Server tool call.

Start from Sperax Ecosystem Crypto & DeFI MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →