Powerful expression evaluation tool for Claude Desktop via Model Context Protocol enabling complex mathematical, string, array, and object manipulations, conditional logic, and data transformations directly within AI conversations.
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A powerful expression evaluation tool for Claude Desktop using the Model Context Protocol (MCP).
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:
To install MCP Expr-Lang for Claude Desktop automatically via Smithery:
npx -y @smithery/cli install @ivan-saorin/mcp-expr-lang --client claude
git clone https://github.com/ivan-saorin/mcp-expr-lang.git cd mcp-expr-lang
go mod download
go build -o bin/server.exe
go build -o bin/server chmod +x bin/server
config.json
:{ "mcpServers": { "eval": { "command": "C:\\path\\to\\mcp-expr-lang\\bin\\server.exe" } } }
{ "mcpServers": { "eval": { "command": "/path/to/mcp-expr-lang/bin/server" } } }
Once installed, you can use the eval
tool directly in your conversations with Claude. Simply ask Claude to evaluate an expression using the tool.
User: Use eval to calculate "10 + 5 * 3"
Claude: [Uses eval tool]
Result: 10 + 5 * 3 = 25
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
MCP Expr-Lang supports all features of the expr-lang engine, including:
For a complete guide to the expression language syntax and capabilities, see the expr-lang documentation.
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
).
If you encounter any issues or have questions:
Contributions are welcome! If you'd like to improve MCP Expr-Lang:
git checkout -b feature/amazing-feature
)git commit -m 'Add some amazing feature'
)git push origin feature/amazing-feature
)This project is licensed under the MIT License - see the LICENSE file for details.
Made with ❤️ by Ivan Saorin
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