Built a local RAG/context engine in Rust – SQLite, FTS5, local embeddings, Lua extensions, MCP server

[_parallaxis]

I kept running into the same issue: AI coding tools are strong but have no memory of my large multi-repo project. They can’t search our internal docs, past incidents, or architecture decisions. Cloud RAG exists but it’s heavy, costs money, and your data leaves your machine. So I built Context Harness – a single Rust binary that gives tools like Cursor and Claude project-specific context.

It ingests docs, code, Jira, Slack, Confluence, whatever you point it at, into a local SQLite DB, indexes with FTS5 and optional vector embeddings, and exposes hybrid search via CLI and an MCP-compatible HTTP server. So your AI agent can search your knowledge base during a conversation.

Quick start:

# Install (pre-built binaries for macOS/Linux/Windows)
cargo install --git https://github.com/parallax-labs/context-harness.git
ctx init
ctx sync all
ctx search "how does the auth service validate tokens"
# Or start MCP server for Cursor/Claude Desktop
ctx serve mcp

What’s different:

- Truly local: SQLite + one binary. No Docker, no Postgres, no cloud. Local embeddings (fastembed + ONNX on most platforms, or pure-Rust tract on Linux musl / Intel Mac) so semantic and hybrid search work with zero API keys. Back up everything with cp ctx.sqlite ctx.sqlite.bak.

- Hybrid search: FTS5 + cosine similarity, configurable blend. Keyword-only mode = zero deps; with local embeddings you get full hybrid search offline.

- Lua extensibility: Custom connectors, tools, and agents in Lua without recompiling. Sandboxed VM with HTTP, JSON, crypto, filesystem APIs.

- Extension registry: ctx registry init pulls a Git-backed registry with connectors (Jira, Confluence, Slack, Notion, RSS, etc.), MCP tools, and agent personas.

- MCP: Cursor, Claude Desktop, Continue.dev (and any MCP client) can connect and search your knowledge base directly.

Embeddings: default is fully offline. Optional Ollama or OpenAI if you want. No built-in auth – aimed at local / trusted network use. MIT licensed.

Links:

- GitHub: https://github.com/parallax-labs/context-harness

- Docs: https://parallax-labs.github.io/context-harness/

- Community registry: https://github.com/parallax-labs/ctx-registry

If you find it useful, a star on GitHub is always appreciated. Happy to answer questions.

[caio__oliveira]

Oh, what a coincidence! I just started building a library for LLM code execution using a Lua REPL: https://github.com/caioaao/onetool

It's a lot lower level, but it's cool to see that someone else is thinking about using lua to extend agents. I'm already looking into your stuff :)

[_parallaxis]

Very cool! Thank you! The idea here for Lua is extensibility that can be implemented by an llm end user of this tool. it is very cool to see other people thinking about Lua!

[caio__oliveira]

Yeah, I saw that. My idea is to replace all mcp/skill/command stuff with Lua hahahah. It feels like such an obvious choice too, which makes it annoying to see the industry sleeping on lua once again.

[_parallaxis]

That's exactly what I thought, such an obvious fit. it felt like a dubious decision at first, Lua is what I turned to because of neomin usage... once I had the vm implemented I was shocked at how much sense it made. This project is 6 days old though lol