MCP 服务器

MCP Expr Lang

README

MCP Expr-Lang

A powerful expression evaluation tool for Claude Desktop using the Model Context Protocol (MCP).

Overview

MCP Expr-Lang provides a seamless integration between Claude AI and the powerful expr-lang expression evaluation engine. This tool allows you to perform complex data manipulations, calculations, and transformations directly within your Claude conversations.

With MCP Expr-Lang, you can:

Evaluate mathematical expressions
Transform and filter arrays and objects
Sort complex data structures
Perform string manipulations
Use conditional logic
And much more!

Installation

Installing via Smithery

To install MCP Expr-Lang for Claude Desktop automatically via Smithery:

npx -y @smithery/cli install @ivan-saorin/mcp-expr-lang --client claude

Prerequisites

Go 1.18 or higher
Claude Desktop application
Git

Step 1: Clone the Repository

git clone https://github.com/ivan-saorin/mcp-expr-lang.git
cd mcp-expr-lang

Step 2: Install Dependencies

go mod download

Step 3: Build the Application

For Windows

go build -o bin/server.exe

For macOS/Linux

go build -o bin/server
chmod +x bin/server

Step 4: Configure Claude Desktop

Open Claude Desktop
Go to Settings
Navigate to the "Advanced" section
Add the following configuration to your config.json:

For Windows

{
  "mcpServers": {
    "eval": {
      "command": "C:\\path\\to\\mcp-expr-lang\\bin\\server.exe"
    }
  }
}

For macOS/Linux

{
  "mcpServers": {
    "eval": {
      "command": "/path/to/mcp-expr-lang/bin/server"
    }
  }
}

Save the configuration and restart Claude Desktop

Usage

Once installed, you can use the eval tool directly in your conversations with Claude. Simply ask Claude to evaluate an expression using the tool.

Basic Example

User: Use eval to calculate "10 + 5 * 3"

Claude: [Uses eval tool]
Result: 10 + 5 * 3 = 25

Complex Example

User: We have users = [{"Name": "John", "Age": 30},{"Name": "Ivan", "Age": 51},{"Name": "Eve", "Age": 15}]
Use eval to calculate "sortBy(users, .Age, "desc")"

Claude: [Uses eval tool]
Result: The expression returns the users sorted by age in descending order:
[
  {"Age": 51, "Name": "Ivan"},
  {"Age": 30, "Name": "John"},
  {"Age": 15, "Name": "Eve"}
]

For more examples please see EXAMPLES

Features

MCP Expr-Lang supports all features of the expr-lang engine, including:

Arithmetic operations: Addition, subtraction, multiplication, division, modulo, exponentiation
String operations: Concatenation, length, uppercase/lowercase conversion
Boolean operations: AND, OR, NOT, comparison operators
Array operations: Mapping, filtering, reducing, sorting
Object manipulation: Property access, transformation
Conditional logic: Ternary operators, if-else expressions
Built-in functions: Mathematical, string, array, and date functions

For a complete guide to the expression language syntax and capabilities, see the expr-lang documentation.

Troubleshooting

Common Issues

Tool not appearing in Claude: Make sure the path in your config.json is correct and Claude Desktop has been restarted.
Execution errors: Check that the expression syntax is correct according to the expr-lang documentation.
Permission issues (macOS/Linux): Ensure the server binary has execution permissions (chmod +x bin/server).