pocketflow/docs/guide.md

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---
layout: default
title: "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 cant solve it, an LLM cant 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:
<div align="center"><img src="https://github.com/the-pocket/PocketFlow/raw/main/assets/utility.png?raw=true" width="400"/></div>
- 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!
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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 to identify weaknesses.
- 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.
- > **Youll likely iterate a lot!** Expect to repeat Steps 36 hundreds of times.
>
> <div align="center"><img src="https://github.com/the-pocket/PocketFlow/raw/main/assets/success.png?raw=true" width="400"/></div>
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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.
- Its 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 projects entry point.