# Ethereum Transaction Builder

Constructs, signs, and decodes Ethereum transactions offline. Generates ERC-20 calldata and calculates gas parameters without exposing keys to network endpoints.

- MCP server · `type=mcp` · Claude Code, Codex, Cursor, GitHub Copilot, Windsurf (Devin Desktop), Cline, Zed, Gemini CLI · ★ 28
- Author: nirholas
- License: not stated · policy=link-only · description only; the file stays with the author
- Source: https://github.com/nirholas/ethereum-wallet-toolkit/tree/HEAD/transaction-mcp-server
- Updated: 2026-10-19
- HTML: https://affpapa.org/en/nevibecode/mcp/ethereum-transaction-builder

## What it 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.

## Requirements
- Needs: Python and uv (commands run via uvx)

## Install

### Claude Code (native platform)

**Platform CLI**
```bash
claude mcp add transaction-mcp-server -- uvx transaction-mcp-server
```
uvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>

### Codex

**Platform CLI**
```bash
codex mcp add transaction-mcp-server -- uvx transaction-mcp-server
```
uvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>

### Cursor

**Config file**
File `.cursor/mcp.json`:
```json
{
    "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>

### GitHub Copilot

**Config file**
File `.vscode/mcp.json`:
```json
{
    "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>

### Gemini CLI

**Platform CLI**
```bash
gemini mcp add transaction-mcp-server uvx transaction-mcp-server
```
uvx runs the command named after the package; if the README names another one, use uvx --from transaction-mcp-server <command>

## When to use it
- 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
- 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

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From the same set: [nirholas/ethereum-wallet-toolkit](https://affpapa.org/en/nevibecode/by/nirholas/ethereum-wallet-toolkit.md) — 5 cards

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