PDL

PDL is a declarative language designed for developers to create reliable, composable LLM prompts and integrate them into software systems. It provides a structured way to specify prompt templates, enforce validation, and compose LLM calls with traditional rule-based systems.

[Quick Start](#quick-start) | [Example](#example-program-a-basic-llm-call) | [GUI](#graphical-experience) | [Key Features](#key-features) | [Documentation](#documentation) | [API Cheat Sheet](#api-cheat-sheet)

What's New

Check out AutoPDL, PDL's prompt optimizer tool Spiess et al. (2025) (opens in a new tab)! AutoPDL can be used to optimize any part of a PDL program. This includes few-shots examples and textual prompts, but also prompting patterns. It outputs an optimized PDL program with optimal values.

For a tutorial on how to use AutoPDL, see AutoPDL (opens in a new tab)

Example Program: A Basic LLM Call

The following program accumulates a single message write a hello world example… and sends it to the ollama/granite-3.2:8b model:

To run this program:

For more information on the pdl CLI see here (opens in a new tab). To try the screenshot on the right live, click here (opens in a new tab).

Graphical Experience

The screenshot on the right (above) shows PDL's graphical user interface. This GUI allows for interactive debugging and live programming. You may install this via brew install pdl on MacOS. For other platforms, downloads are available here (opens in a new tab). You may also kick the tires with a web version of the GUI here (opens in a new tab).

To generate a trace for use in the GUI:

Key Features

• LLM Integration: Compatible with any LLM, including IBM watsonx
• Prompt Engineering:
• Template system for single/multi-shot prompting
• Composition of multiple LLM calls
• Integration with tools (code execution & APIs)
• Development Tools:
• Type checking for model I/O
• Python SDK
• Chat API support
• Live document visualization for debugging
• Control Flow: Variables, conditionals, loops, and functions
• I/O Operations: File/stdin reading, JSON parsing
• API Integration: Native REST API support (Python)

Documentation

• Documentation (opens in a new tab)