Polars MCP Server

MCP server providing Polars API reference documentation via introspection of the installed Polars package and additional information via conceptual guides.

Features

• Polars API searchable by keyword
• Full documentation for any Polars function, method, or class
• Conceptual guides for Polars usage patterns
• pandas to Polars translation guide
• Always up-to-date with your installed Polars version
• No external dependencies or pre-built docs needed

Installation

Important: This server introspects the installed Polars package. Install the same Polars version you use in your project to ensure accurate documentation.

From PyPI

# Or install with latest Polars
uv pip install polars-mcp polars

# Install with your project's Polars version
uv pip install polars-mcp polars==1.35.0

From source

# Clone repository
git clone https://github.com/r-brink/polars-mcp
cd polars-mcp

# Install with uv
uv pip install .

Usage

Add to your MCP settings configuration file.

With uvx

{
    "mcpServers": {
        "polars-mcp": {
            "command": "uvx",
            "args": [
                "--with",
                "polars", # set your Polars version here
                "polars-mcp"
            ]
        }
    }
}

When installing from source

{
    "mcpServers": {
        "polars-mcp": {
            "command": "uv",
            "args": [
                "--directory",
                "/path/to/polars-mcp",
                "run",
                "polars_mcp.py"
            ]
        }
    }
}

Refer to the documentation on the Model Context Protocol website on how to connect to local MCP servers for an extensive guide.

Standalone Testing

# Test the server
python polars_mcp.py --help

# Run with MCP inspector
npx @modelcontextprotocol/inspector uv run polars_mcp.py

Available Tools

polars_get_guide

Get conceptual guides about Polars usage patterns.

Parameters:

• guide (str): Which guide to retrieve
  • 'contexts' - Expression contexts (select, filter, group_by, with_columns, over)
  • 'expressions' - Expression system and composition patterns
  • 'lazy-api' - Lazy evaluation and query optimization
  • 'pandas-to-polars' - Complete pandas to Polars translation guide

Example:

Guide: "pandas-to-polars"
Returns: Complete guide with side-by-side pandas/Polars comparisons

polars_search_api

Search for Polars API elements by keyword.

Parameters:

• query (str): Search term (e.g., "groupby", "filter", "lazy")
• limit (int, optional): Max results (default: 20)
• response_format (str, optional): "markdown" or "json" (default: "markdown")

Example:

Query: "group by"
Returns: List of all group by-related functions and methods

polars_get_docstring

Get complete documentation for a specific API element.

Parameters:

• name (str): Full name (e.g., "DataFrame.filter", "col", "LazyFrame")
• response_format (str, optional): "markdown" or "json" (default: "markdown")

Example:

Name: "DataFrame.filter"
Returns: Full documentation with signature and examples

Available Guides

polars://guides/contexts

Guide to Polars expression contexts:

• What contexts are (select, filter, group_by, with_columns)
• When to use each context
• How contexts affect expression evaluation
• Common patterns for each context

polars://guides/expressions

Complete guide to the Polars expression system:

• What expressions are and how they work
• Composition patterns (chaining, operators, nesting)
• Expression expansion
• Common patterns (aggregations, window functions, conditionals)

polars://guides/lazy-api

Guide to lazy evaluation:

• Eager (DataFrame) vs Lazy (LazyFrame)
• Query optimization (predicate pushdown, projection pushdown)
• When to use each approach
• Best practices for large datasets

polars://guides/pandas-to-polars

• Side-by-side syntax comparisons for all common operations
• Reading data, column selection, filtering, sorting
• Group by aggregations and window functions
• Joins (including semi/anti joins)
• String, datetime, and missing value operations
• Complete worked examples
• Anti-patterns to avoid
• Performance optimization checklist

This guide is specifically optimized for LLMs to quickly translate pandas code to efficient Polars queries.

Why This Server?

• Always current: Documentation reflects your installed Polars version
• Lightweight: No large pre-built documentation databases
• Comprehensive: Combines API reference with conceptual guides
• Migration-friendly: Includes complete pandas translation guide
• Fast: Uses introspection for instant access to documentation

Project Structure

polars-mcp/
├── polars_mcp.py              # Main server
├── pyproject.toml             # Dependencies
├── guides/                    # Conceptual
│   ├── lazy-api.md           # Lazy API guide
│   ├── expressions.md        # Expression patterns
│   ├── contexts.md           # Context behaviors
│   └── pandas-to-polars.md   # pandas to Polars
└── README.md

Contributing

Contributions welcome! Please submit issues or pull requests.