qkb — Query Knowledge Base

An on-device hybrid search engine for Obsidian vaults that understands YAML frontmatter metadata. Combines BM25 keyword search (SQLite FTS5) and vector semantic search (sqlite-vec) with metadata filtering, sibling-document surfacing, and two first-class interfaces: a CLI for humans and an MCP server for LLM agents.

Status: Phase 1 (ingest, search tiers 1–3, CLI, MCP stdio).

Quickstart

1. Install (isolated, like pipx / npm -g):

uv tool install qkb-search

2. Point qkb at your vault — create ~/.config/qkb/config.toml:

[vault]
path = "~/Documents/MyVault"   # your Obsidian vault (read-only to qkb)
name = "MyVault"               # used to build obsidian:// links

3. Opt notes in. Only notes whose frontmatter has a context and/or source property are indexed — and an opted-in note also needs an id and a parseable date (created or date):

---
id: f47ac10b-58cc-4372-a567-0e02b2c3d401
context: homelab
created: 2026-03-15
---

4. Index in two phases, then search:

qkb status                       # verify config, vault, and model resolve
qkb ingest                       # keyword index — fast, no model needed
qkb search "certificate renewal" # keyword (BM25) search works right away
qkb embed                        # compute vectors (downloads the model once; resumable)
qkb query "certificate renewal"  # full hybrid (keyword + semantic) search
qkb mcp                          # stdio MCP server for Claude Code / Desktop

Indexing is split so nothing blocks for hours: qkb ingest builds the keyword index in seconds (no model), so qkb search works immediately; qkb embed then computes the vectors that power semantic/hybrid search. qkb embed is resumable — Ctrl-C is safe, and re-running continues where it left off — and qkb status shows how many vectors are still pending.

No separate service, no compile: embeddings run in-process via ONNX Runtime, whose prebuilt wheels install with the package. The default model is embeddinggemma-300M (multilingual — the same embedding model QMD uses), cached after the first download. Re-running qkb ingest/qkb embed is incremental: unchanged notes are skipped and only new/changed chunks get embedded, so it's cheap to keep up to date.

Claude Code MCP registration:

claude mcp add qkb -- qkb mcp

Documents

• PRD — what we're building and why
• Technical Design — architecture, schema, search algorithms
• Architecture Decision Records — the decision log
• Implementation Plans — milestone-by-milestone build plan

The Short Version

Notes opt in to indexing via frontmatter (context and/or source properties). An ingestion pipeline walks the vault, chunks markdown with structure-aware break-point scoring, embeds in-process (fastembed/ONNX by default; Ollama or GGUF optional), and stores everything in a single SQLite file. A search engine layers BM25 (document-level, weighted columns), vector similarity (chunk-level), and Reciprocal Rank Fusion on top — exposed as qkb search / vsearch / query, qkb get <UUID>, and qkb mcp.

Inspired by QMD's search architecture, adapted for structured knowledge systems with frontmatter metadata.

Installation

qkb is a command-line tool, so install it into an isolated environment — the same idea as pipx or npm i -g:

# Recommended (uv):
uv tool install qkb-search

# Run without installing:
uvx --from qkb-search qkb query "certificate renewal"

# Alternatives (pipx isolates like uv; plain pip uses the current env):
pipx install qkb-search
pip install qkb-search

That's the whole setup — no service, no compile. The default embedding provider runs in-process via fastembed / ONNX Runtime, whose prebuilt wheels ship with the package (the C/C++ work is done upfront by the wheel builders, the way QMD relies on node-llama-cpp's prebuilt native binaries). Requires Python ≥3.11.

The default model is embeddinggemma-300M — the same embedding model QMD uses. GGUF (QMD) and ONNX (qkb) are just different packagings of the same weights for different runtimes; search quality comes from the model, not the file format. The ~310 MB quantized ONNX downloads once on first qkb ingest and is cached.

Embedding providers

Three interchangeable providers, set via [embedding].provider:

provider	how it runs	when to use
local (default)	in-process fastembed / ONNX (prebuilt wheels)	just works — no service, no compile
ollama	the Ollama HTTP API	you already run Ollama (e.g. a Linux box)
gguf	in-process llama-cpp-python (the [gguf] extra)	you want a specific GGUF; compiles on install

Switching provider or model changes the vectors, so run qkb ingest --full afterward to re-embed. Any model in fastembed's catalog also works — e.g. a smaller/faster one:

# ~/.config/qkb/config.toml
[embedding]
provider = "local"
model = "sentence-transformers/paraphrase-multilingual-MiniLM-L12-v2"  # 384-dim, ~220 MB
dimension = 384

License

MIT