HypRAG

Hierarchical retrieval for structured documents. FAISS cosine k-NN seeds a result set, then subtree_expand walks the chunk parent/child graph to pull every parent, sibling, and child of each hit. The flat encoder finds the right region of the document; the hierarchy walker fills in the surrounding context.

+154% Recall@5 on GDPR  ·  +120% on CPython stdlib  ·  <1 ms/query CPU  ·  no GPU

What it does

Most RAG pipelines treat documents as flat bags of chunks. When the right answer lives in paragraph 15(1)(c) of a regulation, flat retrieval returns the chunk for 15(1)(c) — but loses the article header, the surrounding paragraphs, and the chapter context that make the answer interpretable.

HypRAG keeps that structure. Each chunk carries a node_path (e.g. gdpr.ch3.art15.p1.pa) and a depth tag. After the FAISS lookup, subtree_expand returns the parent, the siblings, and the children of every hit. Same recall as flat FAISS at the seed step, but a much higher hit rate after expansion — the answer arrives with its scaffolding intact.

Benchmarks

GDPR (EU 2016/679) — 821 chunks, 20 hand-labeled queries, BGE-base, K=5

Condition	Recall@5	Precision	Latency
FAISS (flat)	0.286	0.590	0.1 ms
FAISS + subtree_expand	0.727	0.441	0.6 ms
Hybrid (BM25+FAISS) + expand	0.683	0.408	1.8 ms

Expansion lift: +154.2 %. BM25 hybrid hurts on regulatory text (uniform vocabulary).

Chunker generalisation — same GDPR corpus, different chunkers

Chunker	Chunks	FAISS	FAISS+expand	Lift
GDPRChunker (domain-specific)	821	0.221	0.549	+148 %
HTMLChunker (generic, no domain)	896	0.256	0.564	+120 %

The expansion lift is algorithm-driven, not chunker-biased. A source-agnostic chunker that only uses HTML heading levels and <ol>/<ul> nesting reaches essentially the same post-expansion recall as a hand-crafted GDPR parser.

CPython stdlib — 16k chunks, K=5

Condition	Recall@5
FAISS (flat)	0.092
FAISS + subtree_expand	0.203

Expansion lift: +120 %.

Reproducing the GDPR numbers:

python -m benchmarks.run_legal_comparison --html-path gdpr_corpus.html
python -m benchmarks.compare_chunkers      --html-path gdpr_corpus.html

Install

pip install hyprag                       # core (faiss, sentence-transformers, numpy)
pip install hyprag[legal]                # adds beautifulsoup4 for HTML chunkers
pip install hyprag[api]                  # adds fastapi + uvicorn for the HTTP server
pip install hyprag[dev]                  # pytest, ruff, mypy

Quick start — Python codebase

from hyprag.retriever import HypragRetriever

r = HypragRetriever()              # default encoder: BAAI/bge-base-en-v1.5
r.index_path("./myproject")        # AST-based chunker, module → class → method

for chunk in r.query("how does the parser handle escape sequences?", k=5):
    print(chunk.depth, chunk.node_path, chunk.start_line)

Quick start — GDPR (or any hierarchical HTML)

from hyprag.chunkers import GDPRChunker     # domain-specific, +154% lift
from hyprag.chunkers import HTMLChunker     # generic, +120% lift, zero domain knowledge
from hyprag.retriever import HypragRetriever

# Fetch the corpus once (per-article from gdpr-info.eu; takes ~5 min)
chunks = GDPRChunker().load()              # or .load(html_path=Path("..."))

r = HypragRetriever()
r.index_chunks(chunks)

for chunk in r.query("when must a data breach be reported?", k=5):
    print(chunk.depth, chunk.node_path)
    print(chunk.text[:200])

HTMLChunker works on any HTML document — Wikipedia, documentation, statutes — using only <h1>–<h6> levels and <ol>/<ul>/<li> nesting as hierarchy signals.

HTTP API

uvicorn api.main:app --reload

POST /index/gdpr, POST /index/codebase, POST /index/texts build indexes. POST /search queries them. Each request is authenticated via X-API-Key; tiering (free / paid) caps vectors, queries/day, and TTL — see api/auth.py.

Every IndexResponse returns depth_distribution and warnings, so callers can verify the chunker recovered the hierarchy as expected without inspecting internals.

Subtree expansion

subtree_expand(results, corpus) is the core algorithm. Given any list of seed chunks and the full corpus, it returns the seeds plus every chunk that is:

• a parent — chunk.node_path matches a seed's parent_path
• a child — chunk.parent_path matches a seed's node_path
• a sibling — same parent_path as a seed

All three are toggleable; max_expand caps the result size. The walk is O(N) per query — cheap enough to run on every search.

What's deliberately not here

• No geometry. Earlier versions used a Poincaré-ball backend for hyperbolic embeddings. Four experiments across two corpora produced numerically identical results to FAISS at up to 257× the latency. Removed in v0.5.0; the git history preserves the code.
• No LLM summaries. Tested; recall regressed. Not coming back.
• No cross-encoder reranking by default. bge-reranker-base hurt on code (Recall@5 0.349 → 0.080). Plug your own in if you have a domain-tuned one.
• No BM25 by default. Hurts on legal text (uniform vocabulary). Opt-in per-request via HybridRetriever for code corpora where identifiers carry signal.

Status

v0.5.x. The algorithm is stable. The API is stable. The chunkers are tested against real corpora. What's missing is a hosted demo and packaging polish.

License

MIT.