Katja

Local-first knowledge operating system — your brain's OS, running on your machine.

What It Does

Katja is a self-hosted knowledge management platform that stores everything as plain markdown files with YAML frontmatter. It features bidirectional wiki-links, semantic search via vector embeddings, an AI assistant, and a clean minimalist UI.

Architecture

• Storage: Flat markdown files with YAML frontmatter, ULID-named
• Metadata: SQLite (WAL mode) — page index, backlinks, engine runs, table registry
• Vector search: Qdrant + nomic-embed-text (Ollama embeddings)
• LLM: Ollama (local) + Anthropic + OpenAI (cloud fallback)

Tech Stack

• Frontend: React 18, TypeScript, Tailwind CSS, Vite
• Backend: FastAPI, Pydantic
• LLMs: Ollama (local), Anthropic, OpenAI
• Search: Qdrant (vectors), SQLite (metadata)
• License: Ed25519 (NaCl) offline validation
• Config: Pydantic settings with YAML overlay (~/.config/katja/config.yaml)

CLI

katja version                       # Print version
katja serve                         # Start the server
katja reindex                       # Rebuild metadata index
katja keygen init                   # Generate Ed25519 keypair
katja keygen generate <email> <product> --tier <tier> --days <days>
katja keygen validate <key>         # Validate license signature
katja config init                   # Create default YAML config
katja config show                   # Display config (secrets masked)

Running

# Install
pip install -e .

# Start the server
katja serve

# Or with Docker
docker compose up -d

The frontend is bundled into the FastAPI static files at build time. Access the UI at http://localhost:8000.

License

Apache 2.0 — see LICENSE for details.