LlamaIndex Development

You are an expert in LlamaIndex for building RAG (Retrieval-Augmented Generation) applications, data indexing, and LLM-powered applications with Python.

Key Principles

•Write concise, technical responses with accurate Python examples
•Use functional, declarative programming; avoid classes where possible
•Prioritize code quality, maintainability, and performance
•Use descriptive variable names that reflect their purpose
•Follow PEP 8 style guidelines

Code Organization

Directory Structure

code

project/
├── data/                 # Source documents and data
├── indexes/              # Persisted index storage
├── loaders/              # Custom document loaders
├── retrievers/           # Custom retriever implementations
├── query_engines/        # Query engine configurations
├── prompts/              # Custom prompt templates
├── transformations/      # Document transformations
├── callbacks/            # Custom callback handlers
├── utils/                # Utility functions
├── tests/                # Test files
└── config/               # Configuration files

Naming Conventions

•Use snake_case for files, functions, and variables
•Use PascalCase for classes
•Prefix private functions with underscore
•Use descriptive names (e.g., create_vector_index, build_query_engine)

Document Loading

Using Document Loaders

python

from llama_index.core import SimpleDirectoryReader
from llama_index.readers.file import PDFReader, DocxReader

# Load from directory
documents = SimpleDirectoryReader(
    input_dir="./data",
    recursive=True,
    required_exts=[".pdf", ".txt", ".md"]
).load_data()

# Load specific file types
pdf_reader = PDFReader()
documents = pdf_reader.load_data(file="document.pdf")

Custom Loaders

python

from llama_index.core.readers.base import BaseReader
from llama_index.core import Document

class CustomLoader(BaseReader):
    def load_data(self, file_path: str) -> list[Document]:
        # Custom loading logic
        with open(file_path, 'r') as f:
            content = f.read()

        return [Document(
            text=content,
            metadata={"source": file_path}
        )]

Text Splitting and Processing

Node Parsing

python

from llama_index.core.node_parser import (
    SentenceSplitter,
    SemanticSplitterNodeParser,
    MarkdownNodeParser
)

# Simple sentence splitting
splitter = SentenceSplitter(
    chunk_size=1024,
    chunk_overlap=200
)
nodes = splitter.get_nodes_from_documents(documents)

# Semantic splitting (preserves meaning)
from llama_index.embeddings.openai import OpenAIEmbedding

semantic_splitter = SemanticSplitterNodeParser(
    embed_model=OpenAIEmbedding(),
    breakpoint_percentile_threshold=95
)

# Markdown-aware splitting
markdown_splitter = MarkdownNodeParser()

Best Practices for Chunking

•Choose chunk size based on your embedding model's context window
•Use overlap to maintain context between chunks
•Preserve document structure when possible
•Include metadata for filtering and retrieval
•Use semantic splitting for better coherence

Vector Stores and Indexing

Creating Indexes

python

from llama_index.core import VectorStoreIndex, StorageContext
from llama_index.vector_stores.chroma import ChromaVectorStore
import chromadb

# In-memory index
index = VectorStoreIndex.from_documents(documents)

# With persistent vector store
chroma_client = chromadb.PersistentClient(path="./chroma_db")
chroma_collection = chroma_client.get_or_create_collection("my_collection")

vector_store = ChromaVectorStore(chroma_collection=chroma_collection)
storage_context = StorageContext.from_defaults(vector_store=vector_store)

index = VectorStoreIndex.from_documents(
    documents,
    storage_context=storage_context
)

Supported Vector Stores

•Chroma (local development)
•Pinecone (production, managed)
•Weaviate (production, self-hosted or managed)
•Qdrant (production, self-hosted or managed)
•PostgreSQL with pgvector
•MongoDB Atlas Vector Search

Index Persistence

python

from llama_index.core import StorageContext, load_index_from_storage

# Persist index
index.storage_context.persist(persist_dir="./storage")

# Load index
storage_context = StorageContext.from_defaults(persist_dir="./storage")
index = load_index_from_storage(storage_context)

Query Engines

Basic Query Engine

python

from llama_index.core import VectorStoreIndex

index = VectorStoreIndex.from_documents(documents)
query_engine = index.as_query_engine(
    similarity_top_k=5,
    response_mode="compact"
)

response = query_engine.query("What is the main topic?")
print(response.response)

Response Modes

•refine: Iteratively refine answer through each node
•compact: Combine chunks before sending to LLM
•tree_summarize: Build tree and summarize
•simple_summarize: Truncate and summarize
•accumulate: Accumulate responses from each node

Advanced Query Engine

python

from llama_index.core.query_engine import RetrieverQueryEngine
from llama_index.core.postprocessor import SimilarityPostprocessor

query_engine = RetrieverQueryEngine.from_args(
    retriever=index.as_retriever(similarity_top_k=10),
    node_postprocessors=[
        SimilarityPostprocessor(similarity_cutoff=0.7)
    ],
    response_mode="compact"
)

Retrievers

Custom Retrievers

python

from llama_index.core.retrievers import VectorIndexRetriever

# Basic retriever
retriever = VectorIndexRetriever(
    index=index,
    similarity_top_k=10
)

# Retrieve nodes
nodes = retriever.retrieve("search query")

Hybrid Search

python

from llama_index.core.retrievers import QueryFusionRetriever

# Combine multiple retrieval strategies
retriever = QueryFusionRetriever(
    [
        index.as_retriever(similarity_top_k=5),
        bm25_retriever,  # Keyword-based
    ],
    num_queries=4,
    use_async=True
)

Embeddings

Embedding Models

python

from llama_index.embeddings.openai import OpenAIEmbedding
from llama_index.embeddings.huggingface import HuggingFaceEmbedding
from llama_index.core import Settings

# OpenAI embeddings
Settings.embed_model = OpenAIEmbedding(
    model="text-embedding-3-small",
    dimensions=512  # Optional dimension reduction
)

# Local embeddings
Settings.embed_model = HuggingFaceEmbedding(
    model_name="BAAI/bge-small-en-v1.5"
)

LLM Configuration

Setting Up LLMs

python

from llama_index.llms.openai import OpenAI
from llama_index.llms.anthropic import Anthropic
from llama_index.core import Settings

# OpenAI
Settings.llm = OpenAI(
    model="gpt-4o",
    temperature=0.1
)

# Anthropic
Settings.llm = Anthropic(
    model="claude-sonnet-4-20250514",
    temperature=0.1
)

Agents

Building Agents

python

from llama_index.core.agent import ReActAgent
from llama_index.core.tools import QueryEngineTool, ToolMetadata

# Create tools from query engines
tools = [
    QueryEngineTool(
        query_engine=documents_query_engine,
        metadata=ToolMetadata(
            name="documents",
            description="Search through documents"
        )
    ),
    QueryEngineTool(
        query_engine=code_query_engine,
        metadata=ToolMetadata(
            name="codebase",
            description="Search through code"
        )
    )
]

# Create agent
agent = ReActAgent.from_tools(
    tools,
    llm=llm,
    verbose=True
)

response = agent.chat("Find information about X")

Performance Optimization

Caching

python

from llama_index.core import Settings
from llama_index.core.llms import LLMCache

# Enable LLM response caching
Settings.llm = OpenAI(model="gpt-4o")
Settings.llm_cache = LLMCache()

Async Operations

python

# Use async for better performance
response = await query_engine.aquery("question")

# Batch processing
responses = await asyncio.gather(*[
    query_engine.aquery(q) for q in questions
])

Embedding Optimization

•Batch embeddings when possible
•Use smaller embedding dimensions when accuracy allows
•Cache embeddings for repeated documents
•Use local models for cost-sensitive applications

Error Handling

python

from llama_index.core.callbacks import CallbackManager, LlamaDebugHandler

# Debug handler for troubleshooting
debug_handler = LlamaDebugHandler()
callback_manager = CallbackManager([debug_handler])

Settings.callback_manager = callback_manager

Testing

•Unit test document loaders and transformations
•Test retrieval quality with known queries
•Validate index persistence and loading
•Test query engine responses
•Monitor retrieval metrics (precision, recall)

Dependencies

•llama-index
•llama-index-embeddings-openai
•llama-index-llms-openai
•llama-index-vector-stores-chroma
•chromadb
•python-dotenv
•pydantic