multilingual-dev-rag

Local-first multilingual RAG for code and technical docs. In-process hybrid retrieval (vector + full-text) with FTS for Cyrillic and other non-ASCII scripts.

pip install multilingual-dev-rag

Русская версия · Apache-2.0

Why this exists

Most local RAG setups pair a multilingual embedding model with a full-text index and call it hybrid search. That works — until your corpus is not in English.

FTS — full-text search: the lexical half of the hybrid. It matches literal words rather than meaning, which is what finds RabbitMQ or obj_k3_gab3 when a vector search only knows they feel like infrastructure and code. Text is split into tokens by a tokenizer, and the whole problem below is that the tokenizer decides which words exist at all.

The embedded engine this is built on (zvec) ships a standard tokenizer that drops non-ASCII tokens entirely (on Windows and Linux — on macOS, curiously, it does not), and a lowercase filter that only folds ASCII. The result is not an error. A query for воркер returns zero rows, a query for RabbitMQ returns rows, and the hybrid quietly degrades to vector-only for half your corpus. Nothing in the logs says so.

The platform split is the nastier half of the story. A package that relied on standard alone would appear to work on a developer's Mac and silently break the moment it shipped to a Linux server — same code, same engine, different tokenizer behaviour per OS. The fix below does not depend on which side of that split you are on: it works everywhere, and is merely redundant where standard already handles Cyrillic.

How the fix works

Swapping the tokenizer does not save you. The engine ships exactly three, and each breaks differently:

¹ On Windows and Linux. On macOS, standard does match Cyrillic — the only platform of the three where it does (verified across the CI matrix on zvec 0.5.1). The text_fts workaround below is therefore redundant on macOS but harmless: its lanes never double-count because Latin is excluded from text_fts.

jieba looks like the answer right up until you measure it at scale: 7 of 9 correct on a five-document probe, pure noise on a real 837-chunk corpus — a query for the exact title word of one document returned three unrelated ones, a different wrong answer per letter case. Worse than standard, which at least stayed honestly silent.

Hence the design: do not pick the best tokenizer — use two, each for what it is good at. The index carries two fields, and every query goes only to the field that can answer it:

text stays byte-for-byte the original: it is what search returns to you. text_fts is derived and internal.

Latin is deliberately excluded from text_fts. If both fields matched RabbitMQ, a document containing it would score twice in the Reciprocal Rank Fusion and outrank documents that match the query's Russian half. Keeping the two lanes disjoint keeps the fusion honest.

Case folding happens in Python, not in the engine: casefold() handles ß/SS and Greek final sigma, which the engine's ASCII-only lowercase filter does not.

What you get

• Hybrid retrieval — vector + full-text, fused with Reciprocal Rank Fusion.
• FTS that survives non-ASCII — verified end-to-end on Russian, German, Greek, French, Arabic.
• No servers — zvec runs in your process. No Qdrant, no Ollama, no Docker.
• Profiles — describe your corpus in JSON; the package stays generic.
• MCP server — exposes rag_search to Claude Code and other MCP clients.

Requirements

Python 3.10–3.13, 64-bit. Everything else follows from zvec's wheels — it ships no sdist, so if there is no wheel for your platform there is no fallback to building from source.

All three wheel-bearing platforms run the full suite in CI, including the eight integration tests that hit the live zvec engine.

On a platform without a wheel, pip install fails with from versions: none. That message means wrong platform, not missing package — no amount of build tooling will help.

3.14 is untested, not unsupported. zvec publishes cp314 wheels and this may well work there, but CI does not run it, so nothing here verifies the claim. requires-python = ">=3.10" has no upper bound, so pip will install on 3.14 — you are the first to find out.

Other requirements:

• 457 MB of disk for the embedding model, downloaded on first index into ~/.cache/huggingface/. Shared across projects; separate from the index.
• On macOS the index goes to ~/.local/share/dev-rag/ (the XDG path), not ~/Library/Application Support. Set ZVEC_DB_PATH if you want the native location.

Install

pip install multilingual-dev-rag

The default embedding model (paraphrase-multilingual-MiniLM-L12-v2, Apache-2.0) is downloaded from Hugging Face on first use and is not bundled.

Configure

Two environment variables:

# Required: the repository you want to index.
export DEV_RAG_ROOT=/path/to/your/repo

# Optional: which files count. Built-in: generic (default), k3_mebel.
# Or a path to your own profile JSON.
export DEV_RAG_PROFILE=generic

DEV_RAG_ROOT is not guessed from the package location, deliberately. An earlier version defaulted to a path near the install directory; when that guess was wrong, globs matched nothing, indexing reported 0 chunks and exited 0.

Two guards replace that guess. A missing root, or one that is not a directory, raises before anything runs. A root that exists but matches no file under the profile's patterns makes dev-rag-index exit 2 with both values printed — an empty index built "successfully" looks healthy right up until a search returns nothing and also says nothing.

Where the index lives

Per user, per corpus — never inside the package:

Linux/macOS   ${XDG_DATA_HOME:-~/.local/share}/dev-rag/<repo>-<hash>/zvec_data
Windows       %LOCALAPPDATA%\dev-rag\<repo>-<hash>\zvec_data

The <hash> is derived from the corpus root's absolute path, so one installation serves several repositories without them colliding. Point DEV_RAG_ROOT somewhere else and you get a separate index, not an overwritten one — otherwise a search would answer confidently from the wrong corpus.

Set ZVEC_DB_PATH to override the location entirely.

The index is derived data: it holds chunks of whatever you indexed, it is rebuilt by dev-rag-index, and it does not belong in version control.

Use

# Index the whole corpus
dev-rag-index --category all --force

# Index one collection
dev-rag-index --category docs --force

# Search from the shell
dev-rag-search "ферма воркеров" --collection docs

The first run is slower than the rest. The embedding model is not bundled: sentence-transformers fetches it from Hugging Face on first use — 457 MB into ~/.cache/huggingface/hub/ (on Windows, C:\Users\<you>\.cache\huggingface\hub\). That is not where the index lives: the model is shared across projects, the index is per corpus. Later runs load it from cache.

For an offline environment, copy the cache from a machine where it is already warm, or point HF_HOME somewhere prepared.

from dev_rag import search

for r in search('усталость воркера', collection='docs', n=5):
    print(f"{r['score']:.4f}  {r['path']}")

As an MCP server

{
  "mcpServers": {
    "dev-rag": {
      "command": "python",
      "args": ["-m", "dev_rag.mcp_server"],
      "env": {
        "DEV_RAG_ROOT": "/absolute/path/to/your/repo",
        "DEV_RAG_PROFILE": "generic"
      }
    }
  }
}

command: "dev-rag-mcp" works too, and on Linux and macOS the two are equivalent. On Windows, prefer python -m — see below.

MCP servers are child processes of the client, not daemons: env is read once at startup. After editing the config, restart the client.

Upgrading on Windows: WinError 32

dev-rag-mcp is an .exe launcher. While the MCP server is running, Windows holds a lock on it, and pip cannot replace it:

ERROR: Could not install packages due to an OSError: [WinError 32]
The process cannot access the file because it is being used by another process:
'...\Scripts\dev-rag-mcp.exe'

Two things about this are worth knowing, because neither is obvious from the message:

• The upgrade mostly went through anyway. Rebuilding the launcher is the last step, so pip has already removed the old version and written the new module, metadata and other scripts. The command exits non-zero while the package is, in fact, upgraded. Verify rather than guess: python -c "import dev_rag; print(dev_rag.__version__)".
• Renaming the locked .exe does not help. A running image cannot be renamed either — that attempt fails with the same error.

Ways out, in order of preference:

1. Launch via python -m dev_rag.mcp_server (as above). Then the lock lands on python.exe, which pip never replaces, and .py files are not held open at all — upgrades just work, with the client still running.
2. Close the MCP client (editor/IDE), upgrade, reopen.

This is not specific to this package: it applies to any console script whose process outlives the upgrade.

Profiles

A profile says which files belong to which collection. generic indexes markdown and Python anywhere; k3_mebel is a worked example for a CAD codebase with .mac macros.

{
  "name": "my_project",
  "collections": { "docs": "my_docs", "code": "my_code", "plans": "my_plans" },
  "index_patterns": {
    "docs":  ["docs/**/*.md"],
    "code":  ["src/**/*.py"],
    "plans": ["rfcs/*.md"]
  }
}

export DEV_RAG_PROFILE=/path/to/my_project.json

Backends

The Qdrant path predates zvec and is kept only as a fallback: nomic-embed-text is English-centric and recalls poorly on Russian. Install it with pip install multilingual-dev-rag[qdrant] and set RAG_BACKEND=qdrant if you need it.

Known limits

• CJK is not supported. Chinese and Japanese have no whitespace between words, so the whitespace tokenizer swallows a sentence as one token. zvec ships a jieba tokenizer for exactly this — it would need a separate field. (Do not reach for jieba on Cyrillic: it indexes it, but shreds it into fragments that match everything. Measured on a real corpus, it ranked worse than returning nothing.)
• Turkish İ/ı is not supported. Caseless matching there is locale-dependent and neither lower() nor casefold() resolves it.
• Indexing is manual. Incremental indexing (--changed-only) is not implemented for the zvec backend; after changing your corpus, re-run a full index.
• One writer. zvec allows many readers but a single writer: do not index while another process holds the collection open for writing.

Origins

Originally built for K3-Мебель — a furniture-design CAD — to give semantic and full-text search over a Russian-language codebase and its documentation. That is where the non-ASCII FTS problem surfaced, and why the fix is measured against a real corpus rather than a toy example.

The k3_mebel profile is that original corpus, kept as a worked example of a hand-tuned profile: Python prototypes, .mac macros, API reference and plans.

License

Apache-2.0. See LICENSE.