---
term: "Chunking"
canonical: https://citable.wiki/glossary/chunking
also_known_as: "Text splitting, passage segmentation"
license: CC BY 4.0
---

# Chunking

**Definition:** Chunking is the step in a retrieval pipeline that splits a page or document into smaller passages — typically a few hundred tokens each, cut at headings, paragraphs or a fixed window — so that each passage can be embedded, indexed and retrieved on its own. Because answer engines retrieve and cite chunks rather than whole pages, chunk boundaries decide what a model actually sees.

You do not control how an answer engine chunks your page, but you control how well the page survives it. Common strategies are fixed-size windows (a few hundred tokens, often with some overlap), recursive splitting on paragraph and then sentence boundaries, and structure-aware splitting on Markdown or HTML headings. Structure-aware splitters are the friendliest, and they are what a clean heading outline, [semantic HTML](/glossary/semantic-html) and a [Markdown version of the page](/guides/serving-markdown-to-llms) make possible.

The failure mode is context loss. Anthropic's [contextual retrieval](https://www.anthropic.com/news/contextual-retrieval) write-up from September 2024 gives the canonical example: a chunk reading "The company's revenue grew by 3% over the previous quarter" is useless on its own, because it does not say which company or which quarter. Their fix — prepending a short generated note on where the chunk sits in the document — cut top-20 retrieval failures by 49% when combined with BM25. You can get much of the same effect at source by writing each section so that it names its own subject.

**Writing for the chunker**

- [ ] One question per H2, phrased as the question
- [ ] The first sentence of each section names the entity and states the answer
- [ ] No "as mentioned above" or unresolved "it" at the start of a section
- [ ] Tables and code blocks short enough to sit inside one chunk with their explanation

## Frequently asked questions

### How long should a section be so that it survives chunking?

Aim for sections that make sense on their own at a few hundred words and open with a self-contained answer. Chunkers differ, but nearly all respect headings and paragraph breaks, so a heading that states the question followed by a 40–70 word direct answer will usually land intact in one chunk.

## Related guides

- [How to write answer-first content that LLMs can quote](https://citable.wiki/guides/how-to-write-answer-first-content)
- [Serving Markdown to LLMs: content negotiation and .md endpoints](https://citable.wiki/guides/serving-markdown-to-llms)
- [Modelling content for answer engines in a headless CMS!](https://citable.wiki/guides/modeling-content-for-answer-engines-in-a-headless-cms)

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Source: https://citable.wiki/glossary/chunking