# Query Rewriting and Expansion — Retrieval-Augmented Generation (RAG)

Source: https://www.geekswithgeeks.com/en/rag/q-rewrite

> Turn messy user questions into good search queries.

## Users do not write search queries

Real questions are short, vague or depend on earlier turns ("and what about contractors?"). Improve them before searching: (1) **condense** the chat history and the follow-up into a **standalone question**; (2) **expand** with synonyms and related terms; (3) **decompose** a complex question into several sub-questions and search for each (**multi-query**); (4) **HyDE**, where the model drafts a hypothetical answer and you search with that text. Each rewrite adds a model call and can drift from the user's intent, so keep the original query in the search too and measure whether the rewrite actually helps.

## Ask better, rank better, send less

Rewrite queries, rerank candidates, diversify results and choose how many chunks to send.

![Four levers: rewrite, rerank, diversify, trim.](assets/figures/rag/section-4-map.svg) — Figure 4.1 — Rewrite, rerank, diversify and trim.

## Condensing a follow-up (prompt template)

A template for turning a follow-up into a standalone question. Not run here.

```text
Given the chat history and the follow-up question, rewrite the follow-up as a
single standalone question that includes all needed context. Do not answer it.

History:
User: How many leave days do employees get?
Assistant: 24 days per year.
Follow-up: and contractors?

Standalone question: How many paid leave days do contractors get per year?
```

**Quiz:** Why condense a follow-up question before retrieval?

- [ ] To make the query longer for no reason
- [x] "and contractors?" alone has no searchable context
- [ ] To avoid embeddings
- [ ] To delete history

*Answer:* "and contractors?" alone has no searchable context. A standalone question carries the meaning the retriever needs.