What are all the parameters of HybridChunker in Docling, and how do you use it with a custom tokenizer?

HybridChunker Parameters#

Here are all HybridChunker() parameters:

Parameter	Type	Default	Description
`tokenizer`	`BaseTokenizer`	default tokenizer	Tokenizer to use (controls `max_tokens`)
`max_tokens`	`int`	from tokenizer	Maximum tokens per chunk (backward compat)
`merge_peers`	`bool`	`True`	Merge undersized chunks with same headings
`repeat_table_header`	`bool`	`True`	Repeat table headers when table is split
`omit_header_on_overflow`	`bool`	`False`	Omit headers if they'd cause overflow
`serializer_provider`	`BaseSerializerProvider`	default	Controls text serialization
`always_emit_headings`	`bool`	`False`	Emit headings even for empty sections
`use_markdown_images`	`bool`	`False`	Serialize images as markdown references and add `has_image` to metadata
`image_placeholder`	`str`	`"![IMAGE]"`	Placeholder for images when `use_markdown_images=False`

Import#

from docling.chunking import HybridChunker

Usage Examples#

Basic usage with max_tokens:

chunker = HybridChunker(max_tokens=512)

Disable peer merging:

chunker = HybridChunker(max_tokens=512, merge_peers=False)

With a custom HuggingFace tokenizer:

from docling_core.transforms.chunker.tokenizer.huggingface import HuggingFaceTokenizer
from transformers import AutoTokenizer

tokenizer = HuggingFaceTokenizer(
    tokenizer=AutoTokenizer.from_pretrained("sentence-transformers/all-MiniLM-L6-v2"),
    max_tokens=256,
)
chunker = HybridChunker(tokenizer=tokenizer)

Full example with chunking and contextualization:

from docling.document_converter import DocumentConverter
from docling.chunking import HybridChunker

converter = DocumentConverter()
result = converter.convert("path/to/document.pdf")
doc = result.document

chunker = HybridChunker(max_tokens=512)
chunks = list(chunker.chunk(dl_doc=doc))

for i, chunk in enumerate(chunks):
    print(f"Text: {chunk.text[:200]}")
    # Contextualized text prepends section headings — use this for embeddings
    enriched = chunker.contextualize(chunk=chunk)
    print(f"Contextualized: {enriched[:200]}")

How HybridChunker Works (4-Stage Pipeline)#

Hierarchical Chunking – Uses an inner HierarchicalChunker to create initial chunks based on document structure.
Group Document Items – Combines consecutive elements (paragraphs, list items, tables) until the token limit is reached.
Split Oversized Items – Splits single elements that exceed max_tokens; tables use LineBasedTokenChunker with header repetition, text uses the semchunk library.
Merge Peers (optional) – When merge_peers=True, merges consecutive undersized chunks that share the same section headings.

The contextualize() method prepends hierarchical section headings to chunk text, which is recommended for embedding in RAG applications.