Planner–Executor: Managing Complexity

In the ReAct pattern, the agent "wings it"—it only thinks one step ahead. For complex projects (like "Write a 10-page research paper"), this leads to a lack of focus.

The Planner–Executor pattern separates "Thinking" from "Doing" by using two distinct roles (or two distinct LLM calls).

1. The Roles

• The Planner: Its only job is to break the big goal into a list of specific, achievable sub-tasks. It does not use tools. It produces a Roadmap.
• The Executor: Its only job is to take a single sub-task from the roadmap and solve it (often using a ReAct loop).

---

2. The Workflow

1. User: "Build me a marketing plan for a new sneaker."
2. Planner:
   • Step 1: Research competitor pricing.
   • Step 2: Identify top 3 social media trends.
   • Step 3: Write ad copy.
3. Executor: Takes Step 1. Runs search tools. Returns result.
4. Executor: Takes Step 2. Runs social media tools. Returns result.
5. Finalizer: Combines all results into the final marketing plan.

---

3. Visualizing the Split

graph TD
    User[Complex Goal] --> Plan[Planner Agent]
    Plan --> List[Sub-task List]
    List --> E1[Executor: Sub-task 1]
    List --> E2[Executor: Sub-task 2]
    List --> E3[Executor: Sub-task 3]
    E1 --> Res[Aggregator]
    E2 --> Res
    E3 --> Res
    Res --> Final[Final Goal Reached]

---

4. Why This is Better for Production

A. Reliability

The Planner can use a very large, smart model (like GPT-4), while the Executor can use a smaller, faster model (like Llama 8B). This saves money and time.

B. Parallelism

Since the sub-tasks are often independent, you can run multiple Executors at the same time!

C. Re-planning

If an Executor fails at Step 2, the system can go back to the Planner and say: "Step 2 failed because the website was down. Please update the plan." The Planner might add a new step: "Search for a cached version of Step 2 data."

---

5. Code Example: Conceptual Planner Output

The Planner should always output a machine-readable format:

{
  "tasks": [
    {"id": 1, "description": "Get CEO name of Nvidia", "tool_required": "search"},
    {"id": 2, "description": "Get CEO name of Intel", "tool_required": "search"},
    {"id": 3, "description": "Compare their net worth", "tool_required": "calculator"}
  ]
}

---

Key Takeaways

• Planner–Executor is for tasks that require more than 3-5 steps.
• The Planner manages the high-level logic and roadmap.
• The Executor focuses on technical completion of a single task.
• This pattern allows for Better error recovery and Parallel execution.