Fine-TuningReActJSONL

Fine-Tuning LLMs With ReAct Reasoning Chains

February 4, 2026·6 min read·3 views

Generic LLMs know a lot about everything and not enough about your specific domain. Fine-tuning bridges that gap -but only if your training data encodes the right reasoning patterns.

The ReAct Pattern

ReAct (Reasoning + Acting) structures each training example as:

  • Thought - The model's internal reasoning about what to do
  • Action - The specific action to take (search, recommend, calculate)
  • Action Input - The parameters for that action
  • Observation - The result of the action

This teaches the model HOW to think, not just WHAT to answer.

Building the Dataset

For each client AI assistant, we create JSONL datasets from:

  • Company websites (product info, policies, FAQs)
  • Product catalogs (specifications, compatibility, pricing)
  • Prompt builder rules (response format, tone, constraints)

Each example follows the ReAct chain, showing the model the complete reasoning process from question to answer.

Case Study: AmatiBot

For Amati Model's ship modeling assistant, we extracted every product detail from their catalog -materials, scales, difficulty levels, tools required. Each training example shows the model reasoning through a customer question:

Thought: The customer is asking about beginner ship models. I should filter by difficulty level and recommend appropriate kits. Action: search_products Action Input: difficulty=beginner, category=ship_kits Observation: Found 12 beginner kits...

The Process

  1. 1.Extract domain knowledge from all available sources
  2. 2.Structure into ReAct reasoning chains
  3. 3.Format as JSONL training data
  4. 4.Fine-tune and evaluate
  5. 5.Deploy with monitoring

This is repeatable across any domain. The key investment is in building high-quality training data with proper reasoning chains.