LangGraph Draft‑Critique‑Rewrite Agent

Overview

This project implements a small LangGraph agent that:

1. Generates a short answer (5‑10 sentences) to a user question.
2. Critiques the draft for completeness, concreteness and absence of filler.
3. If the critique says needs_revision, rewrites the draft incorporating the critique.
4. Loops until the verdict is ok or a maximum of two rewrites is reached.
5. Provides a simple CLI entry point.

The implementation is fully self‑contained and requires only a modern Python interpreter (3.10+).

Installation

# Create and activate a virtual environment (optional but recommended)
python -m venv .venv
source .venv/bin/activate   # On Windows: .venv\Scripts\activate

# Install dependencies
pip install -r requirements.txt

Dependencies

• langgraph
• langchain-openai
• langchain-ollama

Configuration

The agent uses an LLM via the langchain_openai.ChatOpenAI wrapper. It supports both OpenAI and Ollama providers.

Variable	Description	Example
OPENAI_API_KEY	API key for OpenAI.	export OPENAI_API_KEY=sk-…
OLLAMA_BASE_URL	Base URL for a local Ollama instance.	export OLLAMA_BASE_URL=http://localhost:11434/v1

If neither variable is set the agent falls back to the default model gpt-4o-mini (this will require network access to OpenAI).

Usage

Run the CLI entry point:

python agent.py

You will be prompted to type a question. The agent will then display the final draft, the critique, and the verdict.

Example

$ python agent.py
Enter your question: What is the capital of France?

Final Result:
Draft: The capital of France is Paris.
Critique: ok
Verdict: ok

Development Notes

• The graph uses END from langgraph for terminal states.
• The reflect node parses a JSON response, falling back to a default verdict if parsing fails.
• The rewrite node increments the round counter.
• All LLM calls are wrapped in try/except blocks to surface errors clearly.

License

MIT License.