Mcp Simulate

io.github.CryptoAPIs-ioPublished by GitHub account CryptoAPIs-iov0.4.0Updated Oct 24, 2026

MCP server for dry-run Ethereum transaction simulation via Crypto APIs

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Overview

AI-generated overview

A local MCP server that lets an assistant dry-run Ethereum transactions through Crypto APIs, previewing results, gas usage and state changes without broadcast.

What you can do
Simulate Ethereum transactions: dry-run a transfer or contract call on mainnet or sepolia with sender, recipient, value, call data, gas limit and gas price, and preview the outcome, gas usage and state changes before anything is broadcast.
When to use it
Useful when you want an assistant to check what an Ethereum transaction would do before signing or sending it, for example validating a contract call or estimating gas on mainnet or sepolia.
Requirements
Runs locally as a Node.js 18+ process via npx or npm. Needs a Crypto APIs account and API key, supplied through the CRYPTOAPIS_API_KEY environment variable or the --api-key argument. Network access to Crypto APIs is required. HTTP transport is optional and listens on 127.0.0.1 by default.
Before you install
The CRYPTOAPIS_API_KEY is a secret; the README warns that missing or invalid keys may get your IP banned from the Crypto APIs ecosystem. Prefer the environment variable over command-line arguments, which are visible in the process list. If you bind HTTP beyond localhost, set MCP_AUTH_TOKEN and an allowed-hosts list. Simulation is dry-run only and does not broadcast transactions.

Installation

In SourceWeft

  1. Open Mcp Simulate in the dashboard and add it to a workspace.
  2. Enable the server for the chats that should use its tools.

Desktop only via STDIO. STDIO servers start a local process, so they need the SourceWeft desktop host.

Other MCP clients

Follow the launch instructions in the repository.

README

@cryptoapis-io/mcp-simulate

MCP server for Crypto APIs Simulate product. Dry-run Ethereum transactions to preview results without broadcasting.

API Version: Compatible with Crypto APIs version 2024-12-12

Features

  • Simulate Ethereum transactions before broadcasting
  • Preview transaction results, gas usage, and state changes
  • Ethereum only (mainnet, sepolia) — the underlying API endpoint has no blockchain parameter

Prerequisites

Installation

bash
npm install @cryptoapis-io/mcp-simulate

Or install all Crypto APIs MCP servers: npm install @cryptoapis-io/mcp

Usage

bash
# Run with API keynpx @cryptoapis-io/mcp-simulate --api-key YOUR_API_KEY
# Or use environment variableexport CRYPTOAPIS_API_KEY=YOUR_API_KEYnpx @cryptoapis-io/mcp-simulate
# HTTP transport (listens on 127.0.0.1; see "Exposing the server beyond localhost")npx @cryptoapis-io/mcp-simulate --transport http --port 3000 --api-key YOUR_API_KEY

Claude Desktop

Add to your Claude Desktop config (~/Library/Application Support/Claude/claude_desktop_config.json on macOS, %APPDATA%\Claude\claude_desktop_config.json on Windows):

json
{  "mcpServers": {    "cryptoapis-simulate": {      "command": "npx",      "args": ["-y", "@cryptoapis-io/mcp-simulate"],      "env": {        "CRYPTOAPIS_API_KEY": "your_api_key_here"      }    }  }}

Cursor

Add to .cursor/mcp.json (project) or ~/.cursor/mcp.json (global):

json
{  "mcpServers": {    "cryptoapis-simulate": {      "command": "npx",      "args": ["-y", "@cryptoapis-io/mcp-simulate"],      "env": {        "CRYPTOAPIS_API_KEY": "your_api_key_here"      }    }  }}

MCP Inspector

bash
npx @modelcontextprotocol/inspector npx @cryptoapis-io/mcp-simulate --api-key YOUR_API_KEY

n8n

  1. Start the server in HTTP mode:
    bash
    npx @cryptoapis-io/mcp-simulate --transport http --port 3000 --api-key YOUR_API_KEY
  2. In your n8n workflow, add an AI Agent node
  3. Under Tools, add an MCP Client Tool and set the URL to http://localhost:3000/mcp

n8n in Docker: localhost inside the container is not your machine. Start the server with --host 0.0.0.0 and MCP_AUTH_TOKEN set (see Exposing the server beyond localhost), use http://host.docker.internal:3000/mcp as the URL, and add an Authorization: Bearer <token> header to the MCP Client Tool credential.

All servers default to port 3000. Use --port to assign different ports when running multiple servers.

Available Tools

simulate_evm

Simulate an Ethereum transaction (dry run). Ethereum only — the underlying endpoint has no blockchain parameter.

ParameterDescription
networkNetwork: mainnet or sepolia
fromAddressSender address
toAddressRecipient address
valueAmount to send (in native coin)
dataContract call data (hex)
gasLimitGas limit
gasPriceGas price

CLI Arguments

ArgumentDescriptionDefault
--api-keyCrypto APIs API keyCRYPTOAPIS_API_KEY env var
--transportTransport type: stdio or httpstdio
--hostHTTP host (use 0.0.0.0 to accept remote connections — requires an auth token with --api-key)127.0.0.1
--auth-tokenBearer token callers must send (Authorization: Bearer <token>); prefer the MCP_AUTH_TOKEN env varMCP_AUTH_TOKEN env var
--allowed-hostsComma-separated Host header allowlist for non-loopback binds—
--portHTTP port3000
--pathHTTP path/mcp
--statelessEnable stateless HTTP modefalse

HTTP API Key Modes

When using HTTP transport, the server supports two API key modes:

  • With --api-key: The key is used for all requests. x-api-key request headers are ignored.
  • Without --api-key: Each request must include an x-api-key header with a valid Crypto APIs key. This enables hosting a public server where each user provides their own key.
bash
# Per-request key mode (multi-tenant)npx @cryptoapis-io/mcp-simulate --transport http --port 3000# Clients send x-api-key header with each request

Exposing the server beyond localhost

HTTP mode listens on 127.0.0.1 by default, so only processes on the same machine can reach it. To accept connections from other machines or containers, bind explicitly and protect the port:

bash
# Startup-key mode: callers must present the token (the server refuses to start without one)export MCP_AUTH_TOKEN=$(openssl rand -hex 32)npx @cryptoapis-io/mcp-simulate --transport http --host 0.0.0.0 --port 3000 --api-key YOUR_API_KEY \  --allowed-hosts mcp.internal.example# Clients send: Authorization: Bearer $MCP_AUTH_TOKEN
# Per-request key mode: no startup key, every request must carry the caller's own x-api-keynpx @cryptoapis-io/mcp-simulate --transport http --host 0.0.0.0 --port 3000

--allowed-hosts restricts the Host header (DNS rebinding protection) when not bound to loopback. Prefer MCP_AUTH_TOKEN over --auth-token: command-line arguments are visible in the process list.

Stdio transport always requires an API key at startup.

Important: API Key Required

Warning: Making requests without a valid API key — or with an incorrect one — may result in your IP being banned from the Crypto APIs ecosystem. Always ensure a valid API key is configured before starting any server.

Remote MCP Server

Crypto APIs provides an official remote MCP server with all tools available via HTTP Streamable transport at https://ai.cryptoapis.io/mcp. Pass your API key via the x-api-key header — no installation required.

License

MIT

Source: README.md at commit 9806134

Tools

0
SourceWeft has not started this package in its sandbox yet, so its tools are not known.

Version history

2
  1. v0.4.0LatestSep 24, 2026
  2. v0.3.1Sep 16, 2026

Score

50% of the applicable checks met

How complete this listing is, computed from the registry entry, the endpoint and public sources. Not a rating of the server and not a statement that it is safe or working today: reachability is a dated check, and no installs or reviews go into the score.

  • Reached in the last 30 days25 pts

    Keep the endpoint answering the MCP handshake; SourceWeft probes it every 30 days.

  • Auth declared10 pts

    Declare the credential headers in the registry entry, or keep the endpoint answering the probe so its auth can be classified.

  • Tools listed15 pts

    Answer tools/list without a credential, or ship a package that starts in a sandbox without one.

  • DescriptionRequired15 pts
  • Logo10 pts
  • Documentation15 pts
  • License10 pts