Planning Your Chain Architecture

Before writing a single prompt, invest time in planning your chain's architecture. Good planning prevents costly rewrites and ensures your chain is robust and maintainable.

The Planning Process

Phase 1: Requirements Gathering

Start by answering these questions:

1. What is the end goal?

   • What output format is needed?
   • What quality bar must it meet?
   • Who will consume the output?

2. What are the inputs?

   • What data will be available?
   • What format will it be in?
   • What variations might exist?

3. What are the constraints?

   • Time/latency requirements?
   • Cost budget?
   • Reliability requirements?

Phase 2: Step Identification

List all the operations needed:

Phase 3: Dependency Mapping

Determine which steps depend on others:

                    ┌─────────────────┐
                    │ Fetch Blog Posts │
                    └────────┬────────┘
                             │
              ┌──────────────┴──────────────┐
              │                             │
    ┌─────────▼─────────┐         ┌────────▼────────┐
    │ Summarize Each    │         │ Categorize by   │
    │ Post              │         │ Topic           │
    └─────────┬─────────┘         └────────┬────────┘
              │                             │
              └──────────────┬──────────────┘
                             │
                    ┌────────▼────────┐
                    │ Match to User   │
                    │ Preferences     │
                    └────────┬────────┘
                             │
                    ┌────────▼────────┐
                    │ Rank and Select │
                    │ Top Stories     │
                    └────────┬────────┘
                             │
                    ┌────────▼────────┐
                    │ Generate        │
                    │ Newsletter      │
                    └────────┬────────┘
                             │
              ┌──────────────┴──────────────┐
              │                             │
    ┌─────────▼─────────┐         ┌────────▼────────┐
    │ Create Subject    │         │ Create Preview  │
    │ Line              │         │ Text            │
    └───────────────────┘         └─────────────────┘

Phase 4: Interface Design

For each step, define inputs and outputs:

const chainArchitecture = {
  steps: {
    summarizePosts: {
      input: {
        posts: "BlogPost[]",
        maxSummaryLength: "number"
      },
      output: {
        summaries: "PostSummary[]"
      }
    },
    categorizePosts: {
      input: {
        posts: "BlogPost[]",
        categories: "string[]"
      },
      output: {
        categorizedPosts: "CategorizedPost[]"
      }
    },
    // ... rest of steps
  }
};

Architecture Patterns

Pattern 1: Linear Pipeline

Best for sequential transformations:

Input → Step1 → Step2 → Step3 → Output

Use when: Each step transforms data for the next in a clear sequence

Pattern 2: Fork-Join

Best for parallel independent processing:

              ┌→ StepA ─┐
Input → Fork ─┼→ StepB ─┼→ Join → Output
              └→ StepC ─┘

Use when: Multiple independent analyses of the same input

Pattern 3: Router

Best for conditional processing:

              ┌→ PathA → Output
Input → Router┼→ PathB → Output
              └→ PathC → Output

Use when: Different inputs need different processing

Pattern 4: Iterative Refinement

Best for quality improvement:

Input → Generate → Evaluate → [Pass?] → Output
              ↑               │
              └─── Refine ◄───┘ (if fail)

Use when: Output quality needs verification and improvement

Planning Document Template

Use this template to document your chain architecture:

# Chain: [Name]

## Overview
[1-2 sentence description of what this chain does]

## Requirements
- Input: [Description of expected input]
- Output: [Description of expected output]
- Latency: [Target time to complete]
- Cost: [Budget per execution]
- Reliability: [Uptime/success rate requirements]

## Architecture
[Diagram or description of step flow]

## Steps

### Step 1: [Name]
- Purpose: [What it does]
- Input: [Schema]
- Output: [Schema]
- Estimated tokens: [Input/Output token estimate]
- Dependencies: [Which steps must complete first]

### Step 2: [Name]
...

## Error Handling
- [Step]: [How errors are handled]
- Fallback strategy: [What happens if chain fails]

## Monitoring
- Key metrics: [What to track]
- Alert conditions: [When to alert]

## Testing Strategy
- Unit tests: [Per-step tests]
- Integration tests: [End-to-end tests]
- Edge cases: [Known edge cases to test]

Exercise: Plan a Chain

Let's plan a complete chain architecture:

Task: Build a chain that takes a GitHub repository URL and generates a comprehensive README.md

Example architecture:

Phase 1: Data Gathering (Parallel)
├── Fetch repo metadata (name, description, stars)
├── Analyze file structure (identify main files)
├── Read package.json / requirements.txt (dependencies)
├── Find existing README (for reference)
└── Identify code samples (entry points)

Phase 2: Analysis (Parallel)
├── Determine project type (library, app, CLI, etc.)
├── Extract installation steps from config files
├── Identify usage patterns from code
└── Find license information

Phase 3: Generation (Sequential)
├── Generate title and badges
├── Generate description section
├── Generate installation section
├── Generate usage section
├── Generate API/reference section (if applicable)
├── Generate contribution section
└── Generate license section

Phase 4: Assembly
├── Combine all sections
├── Verify markdown formatting
└── Validate links and references

Cost and Latency Estimation

Estimating Token Usage

Step	Input Tokens	Output Tokens	Cost Estimate
Summarize	~2000	~500	$0.008
Analyze	~1500	~300	$0.005
Generate	~800	~1000	$0.015
Total	~4300	~1800	$0.028

Estimating Latency

Sequential steps: 3 steps × 2s average = 6s
Parallel phase: max(1.5s, 2s, 1.8s) = 2s
Total estimated: 8s

Architecture Review Checklist

Before implementing, verify:

• Every step has a clear single purpose
• Inputs and outputs are well-defined
• Dependencies are mapped correctly
• Error handling is planned for each step
• Parallelization opportunities are identified
• Cost and latency estimates are acceptable
• Edge cases are considered
• Testing strategy is defined

Key Takeaways

• Planning saves significant implementation and debugging time
• Start with requirements, then identify steps, then map dependencies
• Choose architecture patterns that match your problem
• Document your architecture before implementing
• Estimate costs and latency during planning
• Review architecture against a checklist before building

In the next module, we'll dive into handling errors in prompt chains.