Context Retrieval

Context Retrieval

Context retrieval is the process of finding and assembling the most relevant pieces of information from a knowledge base to ground an AI agent's responses in factual, up-to-date data. It is the backbone of Retrieval Augmented Generation (RAG) and ensures that generated outputs are accurate and verifiable rather than hallucinated.

Workflow

1. Embed the Query: Convert the user's natural-language query into a dense vector representation using an embedding model (e.g., OpenAI text-embedding-3-small, Cohere embed-v3, or an open-source model like bge-large). The embedding captures the semantic meaning of the query so it can be compared against stored documents.

2. Search the Vector Store: Send the query embedding to a vector database (Pinecone, Weaviate, Qdrant, Chroma, etc.) and perform an approximate nearest-neighbor (ANN) search. Request the top-k candidate chunks, typically k = 10–20 to give the reranker enough material to work with.

3. Rerank the Results: Pass the candidate chunks through a cross-encoder reranker (e.g., Cohere Rerank, bge-reranker-large, or a ColBERT model). The reranker scores each chunk against the original query with full attention, producing much more accurate relevance scores than cosine similarity alone. Keep the top-n results (typically n = 3–5).

4. Assemble the Context Window: Concatenate the selected chunks into a single context block, ordered by relevance score descending. Prepend source metadata (file path, URL, page number) to each chunk so the agent can cite its sources. Ensure the total token count fits the model's budget for the context section of the prompt.

5. Generate the Response: Feed the assembled context into the LLM prompt alongside the original query and a system instruction that tells the model to answer only from the provided context. This grounds the response in retrieved facts and reduces hallucination.

6. Validate and Cite: After generation, verify that the answer references information actually present in the retrieved chunks. Attach inline citations or a references section so the user can trace each claim back to a source document.

Key Concepts

• Semantic Search: Uses vector embeddings to find documents by meaning rather than exact keyword match. Excels at paraphrasing and synonym handling but can miss precise technical terms.
• Keyword Search (BM25): Traditional term-frequency search that excels at exact matches and rare terms. Fast and interpretable but blind to synonyms.
• Hybrid Search: Combines semantic and keyword search (e.g., weighted fusion of BM25 + cosine similarity scores) to get the best of both worlds. Most production RAG systems use hybrid retrieval.
• Chunking Strategies: Documents must be split into chunks before indexing. Common strategies include fixed-size token windows (256–512 tokens with 50-token overlap), sentence-boundary splitting, and recursive character splitting. Smaller chunks improve precision; larger chunks preserve more context.
• Embedding Models: The choice of embedding model affects retrieval quality. Larger models (1024+ dimensions) capture more nuance but cost more to store and query. Always benchmark on your domain before choosing.

Usage

To use this skill, you need a pre-indexed knowledge base with document embeddings stored in a vector database. Provide a natural-language query as input. The skill returns the retrieved context block ready for prompt assembly, along with source metadata for citation.

Examples

Example 1: Retrieving Codebase Context for a Code Question

Query: "How does the authentication middleware validate JWT tokens?"

Retrieved Chunks (after reranking):

Assembled Prompt:

Answer the following question using ONLY the provided context. Cite file paths.

Context:
[1] src/middleware/auth.ts:14-38 — export function validateToken(req, res, next) { ... }
[2] docs/auth-flow.md:8-22 — The JWT is signed with HS256 using the JWT_SECRET env var...
[3] tests/auth.test.ts:5-19 — Test cases covering valid token, expired token...

Question: How does the authentication middleware validate JWT tokens?