Ethereum Transaction Builder — Claude Code MCP Server
Constructs, signs, and decodes Ethereum transactions offline. Generates ERC-20 calldata and calculates gas parameters without exposing keys to network endpoints.
claude mcp add transaction-mcp-server -- uvx transaction-mcp-serverWhat Ethereum Transaction Builder does
The server equips your assistant with 15 tools covering legacy, EIP-2930, and EIP-1559 formats. It builds unsigned payloads, signs them, serializes outputs into RLP, and unpacks raw hex strings. Reference datasets for multiple EVM networks are included, covering Base, Arbitrum One, Optimism, and Sepolia.
Four built-in workflows guide token transfers, gas optimization, and payload inspection. The toolkit converts values between wei, gwei, and ether. It also prepares smart contract input data through encode_function_call and encode_transfer.
Signing happens strictly offline. Because the server lacks node communication, it will never broadcast raw transactions to the network on its own.
What it helps with
- Assemble and sign EIP-1559 transactions with custom fee caps
- Encode calldata payloads for standard ERC-20 transfers or contract calls
- Parse raw hex transactions to inspect gas limits and recover signer addresses
- Convert gas values across wei, gwei, and ether units
Example prompts for the agent
- Create an unsigned EIP-1559 transfer of 0.25 ETH on Arbitrum One
- Decode raw transaction 0x02f8... and verify gas parameters
- Encode calldata for an ERC-20 transfer of 50 tokens to 0x742d35Cc6634C0532925a3b844Bc9e7595f5b4E2
How to install Ethereum Transaction Builder
Platform CLI
claude mcp add transaction-mcp-server -- uvx transaction-mcp-serveruvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>
Platform CLI
codex mcp add transaction-mcp-server -- uvx transaction-mcp-serveruvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>
Config file
{
"mcpServers": {
"transaction-mcp-server": {
"command": "uvx",
"args": [
"transaction-mcp-server"
]
}
}
}uvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>
Config file
{
"servers": {
"transaction-mcp-server": {
"type": "stdio",
"command": "uvx",
"args": [
"transaction-mcp-server"
]
}
}
}uvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>
Platform CLI
gemini mcp add transaction-mcp-server uvx transaction-mcp-serveruvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>
Step by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about Ethereum Transaction Builder
How to install Ethereum Transaction Builder in Claude Code?
Run claude mcp add transaction-mcp-server -- uvx transaction-mcp-server in your terminal.
What does Ethereum Transaction Builder do?
It builds, signs, validates, and decodes Ethereum transactions across legacy and EIP-1559 formats. It also provides tools to encode calldata and calculate gas parameters.
Does the server broadcast transactions to the Ethereum network?
No, all signing occurs offline without connecting to RPC nodes. You must take the output hex and broadcast it through an external provider.
