LlamaIndex Skill

LlamaIndex Skill

Complete guide for LlamaIndex - data framework for LLM applications.

Triggers

Use this skill when:

• Building RAG applications or document QA systems
• Creating search indexes over documents
• Working with LlamaIndex query engines or retrievers
• Implementing knowledge base systems
• Loading and processing documents for LLM applications
• Keywords: llamaindex, llama_index, index, query engine, retriever, RAG, document loader

Quick Reference

Core Components

---

1. Installation

# Core
pip install llama-index

# With all integrations
pip install llama-index[all]

# Specific integrations
pip install llama-index-llms-openai
pip install llama-index-embeddings-openai
pip install llama-index-vector-stores-chroma
pip install llama-index-readers-file

---

2. Basic Setup

Initialize

from llama_index.core import Settings
from llama_index.llms.openai import OpenAI
from llama_index.embeddings.openai import OpenAIEmbedding

# Configure defaults
Settings.llm = OpenAI(model="gpt-4o", temperature=0.1)
Settings.embed_model = OpenAIEmbedding(model="text-embedding-3-small")
Settings.chunk_size = 1024
Settings.chunk_overlap = 200

Quick Start

from llama_index.core import VectorStoreIndex, SimpleDirectoryReader

# Load documents
documents = SimpleDirectoryReader("./​data").load_data()

# Create index
index = VectorStoreIndex.from_documents(documents)

# Query
query_engine = index.as_query_engine()
response = query_engine.query("What is the main topic?")
print(response)

---

3. Document Loading

File Readers

from llama_index.core import SimpleDirectoryReader

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

# Load specific files
documents = SimpleDirectoryReader(
    input_files=["./​doc1.pdf", "./​doc2.txt"]
).load_data()

Specialized Readers

from llama_index.readers.file import PDFReader, DocxReader
from llama_index.readers.web import SimpleWebPageReader

# PDF
pdf_reader = PDFReader()
documents = pdf_reader.load_data(file="document.pdf")

# Web pages
web_reader = SimpleWebPageReader()
documents = web_reader.load_data(urls=["https://example.com"])

# Database (requires llama-index-readers-database)
from llama_index.readers.database import DatabaseReader
reader = DatabaseReader(uri="postgresql://...")
documents = reader.load_data(query="SELECT * FROM articles")

Create Documents Manually

from llama_index.core import Document

documents = [
    Document(
        text="Content here",
        metadata={"source": "manual", "category": "tech"}
    ),
    Document(
        text="More content",
        metadata={"source": "manual", "category": "science"}
    )
]

---

4. Indices

Vector Store Index

from llama_index.core import VectorStoreIndex

# Create from documents
index = VectorStoreIndex.from_documents(documents)

# Save to disk
index.storage_context.persist(persist_dir="./​storage")

# Load from disk
from llama_index.core import StorageContext, load_index_from_storage

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

With External Vector Store

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

# Create Chroma client
chroma_client = chromadb.PersistentClient(path="./​chroma_db")
collection = chroma_client.get_or_create_collection("my_collection")

# Create vector store
vector_store = ChromaVectorStore(chroma_collection=collection)
storage_context = StorageContext.from_defaults(vector_store=vector_store)

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

Summary Index

from llama_index.core import SummaryIndex

# Good for summarization tasks
index = SummaryIndex.from_documents(documents)
query_engine = index.as_query_engine(response_mode="tree_summarize")
response = query_engine.query("Summarize all documents")

Keyword Table Index

from llama_index.core import KeywordTableIndex

# Good for keyword-based retrieval
index = KeywordTableIndex.from_documents(documents)

---

5. Query Engines

Basic Query Engine

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

response = query_engine.query("What is machine learning?")
print(response)
print(response.source_nodes)  # Retrieved documents

Response Modes

# Refine - iterate through nodes refining answer
query_engine = index.as_query_engine(response_mode="refine")

# Compact - stuff nodes into single prompt
query_engine = index.as_query_engine(response_mode="compact")

# Tree summarize - hierarchical summarization
query_engine = index.as_query_engine(response_mode="tree_summarize")

# Simple summarize - concatenate and summarize
query_engine = index.as_query_engine(response_mode="simple_summarize")

# No text - return nodes only
query_engine = index.as_query_engine(response_mode="no_text")

Streaming

query_engine = index.as_query_engine(streaming=True)

response = query_engine.query("Explain RAG")
for text in response.response_gen:
    print(text, end="", flush=True)

Chat Engine

chat_engine = index.as_chat_engine(chat_mode="condense_question")

# Conversation with memory
response = chat_engine.chat("What is LlamaIndex?")
print(response)

response = chat_engine.chat("How does it compare to LangChain?")
print(response)

# Reset memory
chat_engine.reset()

---

6. Retrievers

Basic Retriever

from llama_index.core.retrievers import VectorIndexRetriever

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

nodes = retriever.retrieve("machine learning")
for node in nodes:
    print(f"Score: {node.score}, Text: {node.text[:100]}...")

Hybrid Retriever

from llama_index.core.retrievers import BM25Retriever
from llama_index.core.retrievers import QueryFusionRetriever

# BM25 (keyword-based)
bm25_retriever = BM25Retriever.from_defaults(
    docstore=index.docstore,
    similarity_top_k=5
)

# Vector retriever
vector_retriever = index.as_retriever(similarity_top_k=5)

# Combine
hybrid_retriever = QueryFusionRetriever(
    retrievers=[bm25_retriever, vector_retriever],
    similarity_top_k=5,
    num_queries=1
)

nodes = hybrid_retriever.retrieve("query")

Auto-Merging Retriever

from llama_index.core.node_parser import HierarchicalNodeParser
from llama_index.core.retrievers import AutoMergingRetriever

# Create hierarchical nodes
node_parser = HierarchicalNodeParser.from_defaults(
    chunk_sizes=[2048, 512, 128]
)
nodes = node_parser.get_nodes_from_documents(documents)

# Build index with leaf nodes
leaf_nodes = [n for n in nodes if n.node_type == "leaf"]
index = VectorStoreIndex(leaf_nodes)

# Retriever that auto-merges to parent nodes
retriever = AutoMergingRetriever(
    index.as_retriever(similarity_top_k=6),
    storage_context=index.storage_context
)

---

7. Node Parsing

Text Splitters

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

# Sentence splitter (default)
splitter = SentenceSplitter(
    chunk_size=1024,
    chunk_overlap=200
)
nodes = splitter.get_nodes_from_documents(documents)

# Token-based
splitter = TokenTextSplitter(
    chunk_size=1024,
    chunk_overlap=200
)

# Semantic (groups by meaning)
from llama_index.embeddings.openai import OpenAIEmbedding
splitter = SemanticSplitterNodeParser(
    embed_model=OpenAIEmbedding(),
    breakpoint_percentile_threshold=95
)

Metadata Extraction

from llama_index.core.extractors import (
    TitleExtractor,
    SummaryExtractor,
    QuestionsAnsweredExtractor,
    KeywordsExtractor
)
from llama_index.core.ingestion import IngestionPipeline

pipeline = IngestionPipeline(
    transformations=[
        SentenceSplitter(chunk_size=512),
        TitleExtractor(),
        SummaryExtractor(summaries=["self"]),
        KeywordsExtractor(keywords=5)
    ]
)

nodes = pipeline.run(documents=documents)

---

8. Agents

Basic Agent

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

# Create tool from query engine
query_engine_tool = QueryEngineTool.from_defaults(
    query_engine=query_engine,
    name="knowledge_base",
    description="Useful for answering questions about the documents"
)

# Create agent
agent = ReActAgent.from_tools(
    tools=[query_engine_tool],
    llm=Settings.llm,
    verbose=True
)

response = agent.chat("What are the main topics covered?")

Custom Tools

from llama_index.core.tools import FunctionTool

def multiply(a: int, b: int) -> int:
    """Multiply two integers."""
    return a * b

def search_web(query: str) -> str:
    """Search the web for information."""
    # Implementation
    return f"Search results for: {query}"

multiply_tool = FunctionTool.from_defaults(fn=multiply)
search_tool = FunctionTool.from_defaults(fn=search_web)

agent = ReActAgent.from_tools(
    tools=[multiply_tool, search_tool, query_engine_tool],
    verbose=True
)

Multi-Document Agent

from llama_index.core.tools import QueryEngineTool

# Create tools for each document collection
tools = []
for name, index in document_indices.items():
    tool = QueryEngineTool.from_defaults(
        query_engine=index.as_query_engine(),
        name=f"{name}_tool",
        description=f"Query the {name} documents"
    )
    tools.append(tool)

agent = ReActAgent.from_tools(tools, verbose=True)

---

9. Evaluation

Response Evaluation

from llama_index.core.evaluation import (
    FaithfulnessEvaluator,
    RelevancyEvaluator,
    CorrectnessEvaluator
)

# Faithfulness - is response grounded in context?
faithfulness = FaithfulnessEvaluator()
result = faithfulness.evaluate_response(response=response)
print(f"Faithfulness: {result.passing}")

# Relevancy - is response relevant to query?
relevancy = RelevancyEvaluator()
result = relevancy.evaluate_response(query="query", response=response)
print(f"Relevancy: {result.passing}")

# Correctness - compare to reference
correctness = CorrectnessEvaluator()
result = correctness.evaluate(
    query="What is X?",
    response="X is Y",
    reference="X is Y and Z"
)

Retrieval Evaluation

from llama_index.core.evaluation import RetrieverEvaluator

# Create evaluation dataset
eval_questions = ["Question 1?", "Question 2?"]
eval_answers = ["Answer 1", "Answer 2"]

evaluator = RetrieverEvaluator.from_metric_names(
    ["mrr", "hit_rate"],
    retriever=retriever
)

results = []
for q, a in zip(eval_questions, eval_answers):
    result = evaluator.evaluate(query=q, expected_ids=[...])
    results.append(result)

---

10. Callbacks and Observability

Basic Callbacks

from llama_index.core.callbacks import CallbackManager, LlamaDebugHandler

# Debug handler
llama_debug = LlamaDebugHandler(print_trace_on_end=True)
callback_manager = CallbackManager([llama_debug])

Settings.callback_manager = callback_manager

# Now all operations are traced
response = query_engine.query("What is RAG?")

# View trace
print(llama_debug.get_event_pairs())

Custom Callback

from llama_index.core.callbacks.base import BaseCallbackHandler
from llama_index.core.callbacks import CBEventType

class MyCallback(BaseCallbackHandler):
    def on_event_start(self, event_type, payload, **kwargs):
        print(f"Start: {event_type}")

    def on_event_end(self, event_type, payload, **kwargs):
        print(f"End: {event_type}")

callback_manager = CallbackManager([MyCallback()])

---

11. Common Patterns

Multi-Index Query

from llama_index.core.query_engine import SubQuestionQueryEngine
from llama_index.core.tools import QueryEngineTool

# Multiple indices
tools = [
    QueryEngineTool.from_defaults(
        query_engine=index1.as_query_engine(),
        name="index1",
        description="Contains information about topic 1"
    ),
    QueryEngineTool.from_defaults(
        query_engine=index2.as_query_engine(),
        name="index2",
        description="Contains information about topic 2"
    )
]

# Sub-question engine decomposes complex queries
query_engine = SubQuestionQueryEngine.from_defaults(
    query_engine_tools=tools
)

response = query_engine.query("Compare topic 1 and topic 2")

Citation Engine

from llama_index.core.query_engine import CitationQueryEngine

citation_engine = CitationQueryEngine.from_args(
    index,
    similarity_top_k=5,
    citation_chunk_size=512
)

response = citation_engine.query("What is machine learning?")
# Response includes citations: [1], [2], etc.
print(response.source_nodes)  # Cited sources

Router Query Engine

from llama_index.core.query_engine import RouterQueryEngine
from llama_index.core.selectors import LLMSingleSelector

# Route queries to appropriate index
query_engine = RouterQueryEngine(
    selector=LLMSingleSelector.from_defaults(),
    query_engine_tools=tools
)

---

Best Practices

1. Chunk wisely - Balance size and context
2. Add metadata - Improve retrieval
3. Evaluate - Measure RAG quality
4. Use streaming - Better UX
5. Persist indices - Avoid recomputation
6. Hybrid retrieval - Combine methods
7. Tune top_k - Balance recall/​precision
8. Custom prompts - Domain-specific
9. Monitor costs - Track LLM usage
10. Version indices - Track data changes