simulate_transaction

SERVERVaultPilot MCP SOURCEvaultpilot-mcp

High RISK CLASS

Category Execute

Parameters 51 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/io-github-szhygulin-vaultpilot-mcp/simulate-transaction.md

WHAT IT DOES

What simulate_transaction does on VaultPilot MCP

AI agents invoke simulate_transaction to trigger actions in VaultPilot MCP. 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.

Parameter	Type	Required	Description
`to`	object	Yes
`data`	string	—	Hex-encoded calldata. Omit for a plain value transfer.
`from`	string	—	msg.sender to simulate from. Omit for a state-independent call; include the user's wallet when the target contract's behavior depends on the caller (e.g. WETH9.
`chain`	string	—
`value`	string	—	Value to send with the call, in wei as a decimal string. Omit for 0. Example: "500000000000000000" for 0.5 ETH.

Parameters from the server's own tool schema.

RISK

Why simulate_transaction is rated High

simulate_transaction executes arbitrary contract code via eth_call to determine outcomes. Although it does not broadcast or sign transactions (which would elevate it to Financial/Destructive), it triggers blockchain smart contract execution with user-controlled parameters.

From the tool's definition Tool description states "Run an eth_call against the chain's RPC to simulate a transaction" and explicitly mentions use cases like "does wrapping ETH by sending to WETH9's fallback succeed, does a custom calldata revert" — these are calls to external smart…

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs simulate_transaction safely

PolicyLayer is an MCP gateway: it sits between your AI agents and VaultPilot MCP, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For simulate_transaction, this is the rule to start with:

simulate_transaction Rate-limited

simulate_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.

View as policy code

policy.json

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

RATE-LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect VaultPilot MCP, apply this rule, and every simulate_transaction call is checked against it from then on.

FAQ

Questions about simulate_transaction

What does the simulate_transaction tool do? +

Run an eth_call against the chain's RPC to simulate a transaction without signing or broadcasting it. Returns { ok, returnData?, revertReason? }. Use this BEFORE prepare_*/send_transaction to verify a contract call does what you expect — e.g. does wrapping ETH by sending to WETH9's fallback succeed, does a custom calldata revert, what selector gets hit. For state-dependent calls (WETH deposit credits msg.sender, ERC-20 transfer debits msg.sender), pass the user's wallet as from. Prepared transactions are also re-simulated automatically at send_transaction time — this tool lets the agent check ahead. NEVER call this on a tx that depends on an approval you just submitted but haven't yet waited on: the approval must be included on-chain (poll get_transaction_status until confirmed) before the dependent tx will simulate correctly — otherwise you get a misleading 'insufficient allowance' revert. It is categorised as a Execute tool in the VaultPilot MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

What parameters does simulate_transaction accept? +

simulate_transaction accepts 5 parameters: to, data, from, chain, value. Required: to. The full parameter table on this page comes from the server's own tool schema.

How do I enforce a policy on simulate_transaction? +

Register the VaultPilot MCP server in PolicyLayer and add a rule for simulate_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 VaultPilot MCP. Nothing to install.

What risk level is simulate_transaction? +

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

Can I rate-limit simulate_transaction? +

Yes. Add a rate_limit block to the simulate_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 simulate_transaction completely? +

Set action: deny in the PolicyLayer policy for simulate_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 simulate_transaction? +

simulate_transaction is provided by the VaultPilot MCP server (vaultpilot-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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