Which vector database should I use?

Choice depends on your deployment model: Pinecone for managed/serverless, Weaviate for hybrid search, Chroma for local development, pgvector for SQL integration, or Qdrant for filtered search. The skill documents tradeoffs for each.

What embedding model should I use with Claude?

Voyage-3-large is Anthropic's recommended embedding model for Claude applications. For code search, use voyage-code-3; for open-source deployments, use bge-large-en-v1.5.

Does this skill cover reranking?

Yes. The skill documents reranking methods including cross-encoders, Cohere Rerank API, maximal marginal relevance (MMR), and LLM-based scoring to improve retrieval quality.

Can I combine keyword and semantic search?

Yes. The skill describes hybrid search, which combines dense retrieval (embeddings) and sparse retrieval (BM25/TF-IDF) with weighted fusion.

Does the quick start example work with other LLMs besides Claude?

The example uses Claude, but the pattern is framework-agnostic. You can swap ChatAnthropic for any LangChain LLM provider and adjust embeddings accordingly.

rag-implementation by wshobson

rag-implementation — detailed patterns and worked examples

Advanced RAG Patterns

Pattern 1: Hybrid Search with RRF

from langchain_community.retrievers import BM25Retriever
from langchain.retrievers import EnsembleRetriever

# Sparse retriever (BM25 for keyword matching)
bm25_retriever = BM25Retriever.from_documents(documents)
bm25_retriever.k = 10

# Dense retriever (embeddings for semantic search)
dense_retriever = vectorstore.as_retriever(search_kwargs={"k": 10})

# Combine with Reciprocal Rank Fusion weights
ensemble_retriever = EnsembleRetriever(
    retrievers=[bm25_retriever, dense_retriever],
    weights=[0.3, 0.7]  # 30% keyword, 70% semantic
)

Pattern 2: Multi-Query Retrieval

from langchain.retrievers.multi_query import MultiQueryRetriever

# Generate multiple query perspectives for better recall
multi_query_retriever = MultiQueryRetriever.from_llm(
    retriever=vectorstore.as_retriever(search_kwargs={"k": 5}),
    llm=llm
)

# Single query → multiple variations → combined results
results = await multi_query_retriever.ainvoke("What is the main topic?")

Pattern 3: Contextual Compression

from langchain.retrievers import ContextualCompressionRetriever
from langchain.retrievers.document_compressors import LLMChainExtractor

# Compressor extracts only relevant portions
compressor = LLMChainExtractor.from_llm(llm)

compression_retriever = ContextualCompressionRetriever(
    base_compressor=compressor,
    base_retriever=vectorstore.as_retriever(search_kwargs={"k": 10})
)

# Returns only relevant parts of documents
compressed_docs = await compression_retriever.ainvoke("specific query")

Pattern 4: Parent Document Retriever

from langchain.retrievers import ParentDocumentRetriever
from langchain.storage import InMemoryStore
from langchain_text_splitters import RecursiveCharacterTextSplitter

# Small chunks for precise retrieval, large chunks for context
child_splitter = RecursiveCharacterTextSplitter(chunk_size=400, chunk_overlap=50)
parent_splitter = RecursiveCharacterTextSplitter(chunk_size=2000, chunk_overlap=200)

# Store for parent documents
docstore = InMemoryStore()

parent_retriever = ParentDocumentRetriever(
    vectorstore=vectorstore,
    docstore=docstore,
    child_splitter=child_splitter,
    parent_splitter=parent_splitter
)

# Add documents (splits children, stores parents)
await parent_retriever.aadd_documents(documents)

# Retrieval returns parent documents with full context
results = await parent_retriever.ainvoke("query")

Pattern 5: HyDE (Hypothetical Document Embeddings)

from langchain_core.prompts import ChatPromptTemplate

class HyDEState(TypedDict):
    question: str
    hypothetical_doc: str
    context: list[Document]
    answer: str

hyde_prompt = ChatPromptTemplate.from_template(
    """Write a detailed passage that would answer this question:

    Question: {question}

    Passage:"""
)

async def generate_hypothetical(state: HyDEState) -> HyDEState:
    """Generate hypothetical document for better retrieval."""
    messages = hyde_prompt.format_messages(question=state["question"])
    response = await llm.ainvoke(messages)
    return {"hypothetical_doc": response.content}

async def retrieve_with_hyde(state: HyDEState) -> HyDEState:
    """Retrieve using hypothetical document."""
    # Use hypothetical doc for retrieval instead of original query
    docs = await retriever.ainvoke(state["hypothetical_doc"])
    return {"context": docs}

# Build HyDE RAG graph
builder = StateGraph(HyDEState)
builder.add_node("hypothetical", generate_hypothetical)
builder.add_node("retrieve", retrieve_with_hyde)
builder.add_node("generate", generate)
builder.add_edge(START, "hypothetical")
builder.add_edge("hypothetical", "retrieve")
builder.add_edge("retrieve", "generate")
builder.add_edge("generate", END)

hyde_rag = builder.compile()

Document Chunking Strategies

Recursive Character Text Splitter

from langchain_text_splitters import RecursiveCharacterTextSplitter

splitter = RecursiveCharacterTextSplitter(
    chunk_size=1000,
    chunk_overlap=200,
    length_function=len,
    separators=["\n\n", "\n", ". ", " ", ""]  # Try in order
)

chunks = splitter.split_documents(documents)

Token-Based Splitting

from langchain_text_splitters import TokenTextSplitter

splitter = TokenTextSplitter(
    chunk_size=512,
    chunk_overlap=50,
    encoding_name="cl100k_base"  # OpenAI tiktoken encoding
)

Semantic Chunking

from langchain_experimental.text_splitter import SemanticChunker

splitter = SemanticChunker(
    embeddings=embeddings,
    breakpoint_threshold_type="percentile",
    breakpoint_threshold_amount=95
)

Markdown Header Splitter

from langchain_text_splitters import MarkdownHeaderTextSplitter

headers_to_split_on = [
    ("#", "Header 1"),
    ("##", "Header 2"),
    ("###", "Header 3"),
]

splitter = MarkdownHeaderTextSplitter(
    headers_to_split_on=headers_to_split_on,
    strip_headers=False
)

Vector Store Configurations

Pinecone (Serverless)

from pinecone import Pinecone, ServerlessSpec
from langchain_pinecone import PineconeVectorStore

# Initialize Pinecone client
pc = Pinecone(api_key=os.environ["PINECONE_API_KEY"])

# Create index if needed
if "my-index" not in pc.list_indexes().names():
    pc.create_index(
        name="my-index",
        dimension=1024,  # voyage-3-large dimensions
        metric="cosine",
        spec=ServerlessSpec(cloud="aws", region="us-east-1")
    )

# Create vector store
index = pc.Index("my-index")
vectorstore = PineconeVectorStore(index=index, embedding=embeddings)

Weaviate

import weaviate
from langchain_weaviate import WeaviateVectorStore

client = weaviate.connect_to_local()  # or connect_to_weaviate_cloud()

vectorstore = WeaviateVectorStore(
    client=client,
    index_name="Documents",
    text_key="content",
    embedding=embeddings
)

Chroma (Local Development)

from langchain_chroma import Chroma

vectorstore = Chroma(
    collection_name="my_collection",
    embedding_function=embeddings,
    persist_directory="./chroma_db"
)

pgvector (PostgreSQL)

from langchain_postgres.vectorstores import PGVector

connection_string = "postgresql+psycopg://user:pass@localhost:5432/vectordb"

vectorstore = PGVector(
    embeddings=embeddings,
    collection_name="documents",
    connection=connection_string,
)

Retrieval Optimization

1. Metadata Filtering

from langchain_core.documents import Document

# Add metadata during indexing
docs_with_metadata = []
for doc in documents:
    doc.metadata.update({
        "source": doc.metadata.get("source", "unknown"),
        "category": determine_category(doc.page_content),
        "date": datetime.now().isoformat()
    })
    docs_with_metadata.append(doc)

# Filter during retrieval
results = await vectorstore.asimilarity_search(
    "query",
    filter={"category": "technical"},
    k=5
)

2. Maximal Marginal Relevance (MMR)

# Balance relevance with diversity
results = await vectorstore.amax_marginal_relevance_search(
    "query",
    k=5,
    fetch_k=20,  # Fetch 20, return top 5 diverse
    lambda_mult=0.5  # 0=max diversity, 1=max relevance
)

3. Reranking with Cross-Encoder

from sentence_transformers import CrossEncoder

reranker = CrossEncoder('cross-encoder/ms-marco-MiniLM-L-6-v2')

async def retrieve_and_rerank(query: str, k: int = 5) -> list[Document]:
    # Get initial results
    candidates = await vectorstore.asimilarity_search(query, k=20)

    # Rerank
    pairs = [[query, doc.page_content] for doc in candidates]
    scores = reranker.predict(pairs)

    # Sort by score and take top k
    ranked = sorted(zip(candidates, scores), key=lambda x: x[1], reverse=True)
    return [doc for doc, score in ranked[:k]]

4. Cohere Rerank

from langchain.retrievers import CohereRerank
from langchain_cohere import CohereRerank

reranker = CohereRerank(model="rerank-english-v3.0", top_n=5)

# Wrap retriever with reranking
reranked_retriever = ContextualCompressionRetriever(
    base_compressor=reranker,
    base_retriever=vectorstore.as_retriever(search_kwargs={"k": 20})
)

Prompt Engineering for RAG

Contextual Prompt with Citations

rag_prompt = ChatPromptTemplate.from_template(
    """Answer the question based on the context below. Include citations using [1], [2], etc.

    If you cannot answer based on the context, say "I don't have enough information."

    Context:
    {context}

    Question: {question}

    Instructions:
    1. Use only information from the context
    2. Cite sources with [1], [2] format
    3. If uncertain, express uncertainty

    Answer (with citations):"""
)

Structured Output for RAG

from pydantic import BaseModel, Field

class RAGResponse(BaseModel):
    answer: str = Field(description="The answer based on context")
    confidence: float = Field(description="Confidence score 0-1")
    sources: list[str] = Field(description="Source document IDs used")
    reasoning: str = Field(description="Brief reasoning for the answer")

# Use with structured output
structured_llm = llm.with_structured_output(RAGResponse)

Evaluation Metrics

from typing import TypedDict

class RAGEvalMetrics(TypedDict):
    retrieval_precision: float  # Relevant docs / retrieved docs
    retrieval_recall: float     # Retrieved relevant / total relevant
    answer_relevance: float     # Answer addresses question
    faithfulness: float         # Answer grounded in context
    context_relevance: float    # Context relevant to question

async def evaluate_rag_system(
    rag_chain,
    test_cases: list[dict]
) -> RAGEvalMetrics:
    """Evaluate RAG system on test cases."""
    metrics = {k: [] for k in RAGEvalMetrics.__annotations__}

    for test in test_cases:
        result = await rag_chain.ainvoke({"question": test["question"]})

        # Retrieval metrics
        retrieved_ids = {doc.metadata["id"] for doc in result["context"]}
        relevant_ids = set(test["relevant_doc_ids"])

        precision = len(retrieved_ids & relevant_ids) / len(retrieved_ids)
        recall = len(retrieved_ids & relevant_ids) / len(relevant_ids)

        metrics["retrieval_precision"].append(precision)
        metrics["retrieval_recall"].append(recall)

        # Use LLM-as-judge for quality metrics
        quality = await evaluate_answer_quality(
            question=test["question"],
            answer=result["answer"],
            context=result["context"],
            expected=test.get("expected_answer")
        )
        metrics["answer_relevance"].append(quality["relevance"])
        metrics["faithfulness"].append(quality["faithfulness"])
        metrics["context_relevance"].append(quality["context_relevance"])

    return {k: sum(v) / len(v) for k, v in metrics.items()}

/rag-implementation

referencesdetails.md

rag-implementation — detailed patterns and worked examples

Advanced RAG Patterns

Pattern 1: Hybrid Search with RRF

Pattern 2: Multi-Query Retrieval

Pattern 3: Contextual Compression

Pattern 4: Parent Document Retriever

Pattern 5: HyDE (Hypothetical Document Embeddings)

Document Chunking Strategies

Recursive Character Text Splitter

Token-Based Splitting

Semantic Chunking

Markdown Header Splitter

Vector Store Configurations

Pinecone (Serverless)

Weaviate

Chroma (Local Development)

pgvector (PostgreSQL)

Retrieval Optimization

1. Metadata Filtering

2. Maximal Marginal Relevance (MMR)

3. Reranking with Cross-Encoder

4. Cohere Rerank

Prompt Engineering for RAG

Contextual Prompt with Citations

Structured Output for RAG

Evaluation Metrics

Third-party checks

Provenance

Topics

What it does

Frequently asked

/rag-implementation

rag-implementationreferencesdetails.md

rag-implementation — detailed patterns and worked examples

Advanced RAG Patterns

Pattern 1: Hybrid Search with RRF

Pattern 2: Multi-Query Retrieval

Pattern 3: Contextual Compression

Pattern 4: Parent Document Retriever

Pattern 5: HyDE (Hypothetical Document Embeddings)

Document Chunking Strategies

Recursive Character Text Splitter

Token-Based Splitting

Semantic Chunking

Markdown Header Splitter

Vector Store Configurations

Pinecone (Serverless)

Weaviate

Chroma (Local Development)

pgvector (PostgreSQL)

Retrieval Optimization

1. Metadata Filtering

2. Maximal Marginal Relevance (MMR)

3. Reranking with Cross-Encoder

4. Cohere Rerank

Prompt Engineering for RAG

Contextual Prompt with Citations

Structured Output for RAG

Evaluation Metrics

Third-party checks

Provenance

Topics

README badge

What it does

Frequently asked

Related skills

referencesdetails.md