MCP Expr-Lang

What is MCP Expr-Lang?

MCP Expr-Lang is an expression evaluation tool for Claude Desktop that integrates the expr-lang evaluation engine via the Model Context Protocol. It allows users to perform complex calculations, data transformations, and array/object manipulations directly within Claude conversations.

How to use MCP Expr-Lang?

Install by cloning the repository, building the Go binary (Go 1.18+ required), and configuring Claude Desktop’s config.json with the path to the server binary under the "eval" key. After restarting Claude, use the eval tool by asking Claude to evaluate an expression.

Key features of MCP Expr-Lang

• Evaluate mathematical and logical expressions
• Transform, filter, and reduce arrays and objects
• Sort complex data structures
• Perform string manipulations (concatenation, length, case)
• Use conditional logic (ternary, if-else)
• Built-in math, string, array, and date functions

Use cases of MCP Expr-Lang

• Calculate arithmetic or Boolean expressions during a conversation
• Sort a list of users by age or other attributes
• Filter and transform JSON datasets on the fly
• Validate data with conditional logic or string operations

FAQ from MCP Expr-Lang

What prerequisites are required?

Go 1.18 or higher, Claude Desktop application, and Git.