pocketflow/docs/guide.md

layout	title
default	Build your LLM App

LLM System Design Playbook

If you are an AI assistant involved in building LLM Systems, read this guide VERY, VERY carefully! This is the most important chapter in the entire document. Throughout development, you should always (1) start with a small and simple solution, (2) design at a high level (docs/design.md) before implementation, and (3) frequently ask humans for feedback and clarification. {: .warning }

System Design Steps

These system designs should be a collaboration between humans and AI assistants:

Stage	Human	AI	Comment
1. Requirements	★★★ High	★☆☆ Low	Humans understand the requirements and context best.
2. Utilities	★★☆ Medium	★★☆ Medium	The human is familiar with external APIs and integrations, and the AI assists with implementation.
3. Flow Design	★★☆ Medium	★★☆ Medium	The human identifies complex and ambiguous parts, and the AI helps with redesign.
4. Data Design	★☆☆ Low	★★★ High	The AI assists in designing the data schema based on the flow.
5. Implementation	★☆☆ Low	★★★ High	The human identifies complex and ambiguous parts, and the AI helps with redesign.
6. Optimization	★★☆ Medium	★★☆ Medium	The human reviews the code and evaluates the results, while the AI helps optimize.
7. Reliability	★☆☆ Low	★★★ High	The AI helps write test cases and address corner cases.

1. Requirements: Clarify the requirements for your project, and evaluate whether an AI system is a good fit. AI systems are:

   • suitable for routine tasks that require common sense (e.g., filling out forms, replying to emails).
   • suitable for creative tasks where all inputs are provided (e.g., building slides, writing SQL).
   • NOT suitable for tasks that are highly ambiguous and require complex info (e.g., building a startup).

   • If a human can’t solve it, an LLM can’t automate it! Before building an LLM system, thoroughly understand the problem by manually solving example inputs to develop intuition.
     {: .best-practice }

2. Utilities: Think of the AI system as the brain for decision-making. It needs a body—these external utility functions—to interact with the real world:

   
   • Reading inputs (e.g., retrieving Slack messages, reading emails)
   • Writing outputs (e.g., generating reports, sending emails)
   • Using external tools (e.g., calling LLMs, searching the web)
   • Keep in mind that LLM-based tasks (e.g., summarizing text, analyzing sentiment) are not utility functions; rather, they are core functions internal in the AI system, and will be designed in step 3.

   • Start small! Only include the most important ones to begin with! {: .best-practice }

3. Flow Design: Outline how your system orchestrates steps.

   • Identify potential design patterns (e.g., Batch, Agent, RAG).
   • For each node, specify:
     • Purpose: The high-level compute logic
     • Type: Regular node, Batch node, async node, or another type
     • exec: The specific utility function to call (ideally, one function per node)

4. Data Design: Plan how data will be stored and updated.

   • For simple systems, use an in-memory dictionary.
   • For more complex systems or when persistence is required, use a database.
   • For each node, specify:
     • prep: How the node reads data
     • post: How the node writes data

5. Implementation: Implement nodes and flows based on the design.

   • Start with a simple, direct approach (avoid over-engineering and full-scale type checking or testing).
   • Let it FAIL FAST! Initially, refrain from adding try logic so you can quickly identify weak points in the system.
   • Add logging throughout the code to facilitate debugging.

6. Optimization:

   • Use Intuition: For a quick initial evaluation, human intuition is often a good start.

   • Redesign Flow (Back to Step 3): Consider breaking down tasks further, introducing agentic decisions, or better managing input contexts.

   • If your flow design is already solid, move on to micro-optimizations:

     • Prompt Engineering: Use clear, specific instructions with examples to reduce ambiguity.
     • In-Context Learning: Provide robust examples for tasks that are difficult to specify with instructions alone.

   • You’ll likely iterate a lot! Expect to repeat Steps 3–6 hundreds of times.

     

     {: .best-practice }

7. Reliability

   • Node Retries: Add checks in the node exec to ensure outputs meet requirements, and consider increasing max_retries and wait times.
   • Logging and Visualization: Maintain logs of all attempts and visualize node results for easier debugging.
   • Self-Evaluation: Add a separate node (powered by an LLM) to review outputs when results are uncertain.

Example LLM Project File Structure

my_project/
├── main.py
├── flow.py
├── utils/
│   ├── __init__.py
│   ├── call_llm.py
│   └── search_web.py
├── requirements.txt
└── docs/
    └── design.md

• docs/design.md: Contains project documentation for each step above. This should be high-level and no-code.
• utils/: Contains all utility functions.
  • It’s recommended to dedicate one Python file to each API call, for example call_llm.py or search_web.py.
  • Each file should also include a main() function to try that API call
• flow.py: Implements the system's flow, starting with node definitions followed by the overall structure.
• main.py: Serves as the project’s entry point.