AI Design Patterns Quick Reference¶

Quick lookup for common patterns. See individual chapters for detailed implementation.

Retrieval Patterns¶

Pattern	Use Case	Key Tradeoff
Basic RAG	Simple Q&A over documents	Easy to implement, limited accuracy
Hybrid Search	Combining semantic + keyword	Better recall, more complexity
Reranking	High-precision retrieval	Accuracy vs latency
Query Expansion	Ambiguous queries	Better recall, more tokens
HyDE	No direct matches expected	Creative, but can hallucinate
Parent-Child Chunking	Need surrounding context	Memory overhead

Query → Embed → Vector Search → Rerank → Top-K → Generate
              ↓
         BM25 Search ─────────┘ (hybrid)

Generation Patterns¶

Pattern	Use Case	Key Tradeoff
Zero-Shot	Simple tasks	Fast, less reliable
Few-Shot	Need format control	Token cost
Chain-of-Thought	Reasoning tasks	Latency, shows work
Self-Consistency	High-stakes answers	3-5x cost
Structured Output	API responses	Constrained creativity

Agent Patterns¶

Pattern	Use Case	Complexity
ReAct	Tool-using agents	Medium
Plan-and-Execute	Multi-step tasks	High
Multi-Agent Debate	Verification	High
Human-in-the-Loop	High-stakes actions	Medium
Swarm / Handoff	Specialised sub-agents	High
Advisor / Executor	Cheap model runs the loop, strong model consulted at decision points	Medium
Orchestrator + isolated subagents	Parallel work without context contention	High

Advisor / executor, added in 2026, is the cost-quality lever worth knowing: an inexpensive executor drives the agent loop and calls a stronger advisor model at decision points, passing the transcript and receiving a plan or correction. It is a cost claim rather than a quality claim: pairing a low-effort executor with a stronger advisor can beat the cost-quality line that executor traces by raising its own effort, while the top scores still belong to maximum effort at higher cost. Published figures are vendor-benchmarked, so measure on your own tasks. Consult rate is the metric to watch: if the executor consults on nearly every step you have bought an expensive model with extra latency.

Orchestrator plus isolated subagents is where the single-versus-multi-agent argument landed. Subagents get their own context and return summaries, with no peer-to-peer channel between them. Context is what is isolated, not state: managed platforms typically share one sandbox, filesystem, and credential set across the roster. Vendor platforms enforce the limits that make it work in practice, typically one level of delegation and a cap on roster size, which is a good default even when your framework does not enforce it.

┌─────────────────────────────────────────┐
│              REACT LOOP                  │
│                                         │
│  Observe → Think → Act → Observe → ...  │
│              ↓                          │
│         [Tool Call]                     │
│              ↓                          │
│         [Result]                        │
└─────────────────────────────────────────┘

Agentic Coding Patterns (2026)¶

Pattern	Use Case	Key Tool
Scaffold → Implement → Verify	Full feature development	Claude Code / OpenHands
Read-Plan-Edit	Refactoring existing code	Claude Code text_editor
Test-Driven Agent	High reliability code	Agent writes tests first
Shadow Review	PR quality gate	Agent reviews diff before merge
CLAUDE.md Manifest	Project context injection	Claude Code CLAUDE.md file
Sub-Agent Parallelism	Large codebase changes	Multiple agents per module

┌────────────────────────────────────────────────────────┐
│              AGENTIC CODING LOOP                        │
│                                                        │
│  Understand → Plan → Implement → Run Tests → Fix       │
│      ↑             (bash + text_editor tools)    │     │
│      └──────────── Iterate until tests pass ────┘     │
│                                                        │
│  [CLAUDE.md injects: coding style, test commands,     │
│   forbidden patterns, architecture decisions]          │
└────────────────────────────────────────────────────────┘

When to use which tool:

Need full autonomy + CLI → Claude Code
Need open-source + any LLM → OpenHands / Cline
Need tight IDE integration → Cursor / Windsurf
Need reproducible pipelines → OpenHands in Docker CI

Reliability Patterns¶

Pattern	Problem Solved	Implementation
Retry with Backoff	Transient failures	Exponential backoff
Circuit Breaker	Cascading failures	Fail-fast after threshold
Fallback Model	Primary unavailable	Secondary model
Timeout	Slow responses	Cancel + fallback
Bulkhead	Resource isolation	Separate pools

# Reliability stack
@circuit_breaker(failure_threshold=5)
@retry(max_attempts=3, backoff=exponential)
@timeout(seconds=30)
@fallback(model="gpt-4o-mini")
async def generate(prompt):
    return await primary_model.generate(prompt)

Caching Patterns¶

Pattern	Hit Rate	Use Case
Exact Match	Low	Identical queries
Semantic Cache	Medium	Similar queries
KV Cache	High	Same prefix
Response Cache	Varies	Deterministic outputs

Security Patterns¶

Pattern	Threat	Implementation
Input Validation	Prompt injection	Sanitize, detect
Output Filtering	Data leakage	PII detection, blocklists
Tenant Isolation	Cross-tenant access	Filter at query time
Rate Limiting	Abuse	Per-user/tenant limits

Input → Validate → Sanitize → LLM → Filter → Validate → Output

Evaluation Patterns¶

Pattern	Use Case	Metrics
Golden Set	Regression testing	Pass rate
LLM-as-Judge	Quality scoring	1-5 scale
Human Eval	Ground truth	Agreement rate
A/B Testing	Production comparison	User metrics

Cost Optimization Patterns¶

Pattern	Savings	Tradeoff
Model Routing	50-70%	Complexity
Caching	20-40%	Staleness
Prompt Compression	10-30%	Quality risk
Batch Processing	30-50%	Latency

Query → Classify → Route → [Small Model] or [Large Model]
                      ↓
              [Cheap: 80%]  [Expensive: 20%]

Anti-Patterns to Avoid¶

Anti-Pattern	Problem	Better Approach
Context Stuffing	Token waste	Retrieve relevant only
Retry Forever	Resource exhaustion	Circuit breaker
Trust All Output	Hallucination	Verify, ground
Single Model	Single point of failure	Multi-provider
No Observability	Blind debugging	Trace everything
Infinite Agentic Loop	Agent spins without progress	Max turns + Critic agent
Over-trusting Computer-Use	Agent clicks wrong UI elements	Screenshot validation + HITL
No CLAUDE.md / Manifest	Agent lacks project context	Always provide coding manifest
Thinking Mode Always On	3-10x cost with no benefit	Gate on complexity classifier

Pattern Selection Guide¶

Starting a new project? 1. Begin with Basic RAG 2. Add reranking when precision matters 3. Add hybrid search for keyword-heavy content

Need reliability? 1. Start with retry + timeout 2. Add circuit breaker for external calls 3. Add fallback models for critical paths

Cost concerns? 1. Implement semantic caching first 2. Add model routing for query complexity 3. Batch where latency allows

See 15-ai-design-patterns/ for detailed implementations