io.github.shinpr/mcp-local-rag MCP Server

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MCP Local RAG

<p align="center"> <strong>English</strong> | <a href="README.zh-CN.md">简体中文</a> | <a href="README.de.md">Deutsch</a> | <a href="README.es.md">Español</a> | <a href="README.pt-BR.md">Português (Brasil)</a> | <a href="README.fr.md">Français</a> </p>

Search private documents from an MCP client or the terminal without sending them to an embedding API.

mcp-local-rag indexes PDF, DOCX, Markdown, and text files on your machine. Search combines semantic similarity with keyword matching, so queries can match both intent and exact technical terms such as API names, class names, and error codes.

Features

• Runs locally: Document parsing, embeddings, storage, and search run on your machine. After the initial model download, text ingestion and search work offline.
• Hybrid search: Semantic retrieval finds related concepts, while keyword matching boosts exact technical terms.
• Configurable embeddings: Choose a Hugging Face embedding model that fits the language and domain of your documents.
• Semantic chunking: Documents are split at topic boundaries instead of fixed character counts. Markdown code blocks stay intact.
• MCP and CLI: Use the same index from an AI coding tool or directly from the terminal.

No API key, Docker, Python, or external database is required.

Quick Start

Requirements

• Node.js 22 or later
• Internet access on first use to download the npm package and embedding model
• A directory containing the documents you want to search

Set BASE_DIR to that directory. It is also the security boundary for file operations. Replace /absolute/path/to/your/documents below with the directory's absolute path.

mcp-local-rag uses the standard MCP protocol over a local stdio server, so it works with AI coding tools and other MCP hosts that support local MCP servers.

Use one of the examples below, or register npx -y mcp-local-rag and set BASE_DIR using your client's MCP configuration format.

For Claude Code: Run this command:

claude mcp add local-rag --scope user --env BASE_DIR=/absolute/path/to/your/documents -- npx -y mcp-local-rag

For Codex: Add to ~/.codex/config.toml:

[mcp_servers.local-rag]
command = "npx"
args = ["-y", "mcp-local-rag"]

[mcp_servers.local-rag.env]
BASE_DIR = "/absolute/path/to/your/documents"

For OpenCode: Add to ~/.config/opencode/opencode.json (or opencode.jsonc):

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "local-rag": {
      "type": "local",
      "command": ["npx", "-y", "mcp-local-rag"],
      "environment": {
        "BASE_DIR": "/absolute/path/to/your/documents"
      }
    }
  }
}

For Cursor: Add to ~/.cursor/mcp.json:

{
  "mcpServers": {
    "local-rag": {
      "command": "npx",
      "args": ["-y", "mcp-local-rag"],
      "env": {
        "BASE_DIR": "/absolute/path/to/your/documents"
      }
    }
  }
}

Restart the client, then ask it to build the index:

Sync all documents in the configured root and wait until it finishes.

The first sync downloads the default embedding model (about 90 MB) and may take 1–2 minutes before ingestion starts. Later runs use the local cache.

Once the sync completes:

What does the API documentation say about authentication?

CLI Quick Start

To use the CLI without an MCP client:

npx mcp-local-rag ingest ./docs/
npx mcp-local-rag query "authentication API"

The CLI uses the current directory as its document root by default. Run both commands from the same directory so they use the same default index, or set BASE_DIR and DB_PATH explicitly.

Why This Exists

Some document sets cannot be sent to a hosted embedding service because of confidentiality or organizational policy. Keeping the index local makes them searchable without adding a per-query API cost.

Semantic search alone can miss exact identifiers that matter in technical documentation. Keyword reranking keeps those terms visible without giving up natural-language retrieval.

Supported Content

Input	How to ingest
PDF, DOCX, TXT, Markdown	File ingestion or directory sync
HTML already fetched by the client	ingest_data; cleaned with Readability and converted to Markdown
Plain text or Markdown held in memory	ingest_data with a stable source identifier

HTML fetching is not built into the server. An MCP client can fetch a page and pass its HTML to ingest_data.

Excel, PowerPoint, standalone images, and source-code file extensions are not supported by file ingestion. PDFs can optionally use a local vision model to describe figures, but this is not OCR or image search.

MCP Tools

Tool	Purpose
sync_start	Reconcile the index with all configured roots or one path
sync_status	Poll a running sync job
ingest_file	Ingest or replace one file
ingest_data	Ingest text, Markdown, or HTML already held by the client
query_documents	Search with semantic matching and keyword boost
read_chunk_neighbors	Read surrounding chunks from a search result
list_files	Show supported files and their ingestion state
delete_file	Delete an indexed file or an ingest_data item
status	Show index and search status

Syncing a Document Root

sync_start ingests new and changed files, skips byte-identical files, and removes index entries for files that no longer exist:

Sync everything under the configured document roots and wait for completion.

The tool returns a jobId immediately. Clients should poll sync_status until its state becomes succeeded or failed. There is no visual mode during sync; changed PDFs are ingested as text.

Only one sync job is retained by the server process. A newer job replaces a finished record, and restarting the server discards it.

Ingesting One File

ingest_file accepts PDF, DOCX, TXT, and Markdown. MCP file paths must be absolute and must stay inside a configured document root:

Ingest the document at /Users/me/docs/api-spec.pdf.

Re-ingesting the same path replaces its existing chunks.

Searching and Reading More Context

What does the API documentation say about authentication?
Find the documented behavior of ERR_CONNECTION_REFUSED.

Results contain the text, source path, title, chunk index, and relevance score. Pass the chunkIndex and either filePath or source from a result to read_chunk_neighbors when the answer needs more context:

Read the surrounding chunks for that authentication result.

Both query_documents and list_files accept an optional absolute scope path prefix, or a list of prefixes. A prefix matches the exact path and its descendants.

Ingesting HTML

Use ingest_data after the MCP client fetches a page:

Fetch https://example.com/docs and ingest the HTML.

The server extracts the main article, converts it to Markdown, and stores it under the supplied source identifier. Reusing the same source updates the existing content.

Respect the source site's terms and copyright when indexing external content.

PDF Figures

Visual mode adds a generated caption for figure-heavy PDF pages. It is opt-in and does not load a vision model during normal ingestion.

Ingest /Users/me/docs/research-paper.pdf with visual: true.

npx mcp-local-rag ingest ./docs/research-paper.pdf --visual

Profile	Model cache	Use case
fast (default)	about 250 MB	Lightweight visual indexing
quality	about 2.9 GB	Figures containing labels, annotations, or other in-image text

Select the larger model with visualQuality: "quality" over MCP or --visual-quality quality over CLI. Measured CPU inference was about twice as slow as fast, though results depend on hardware and model updates.

Captions are auxiliary text, not faithful transcriptions. Treat retrieved captions and document text as untrusted input rather than instructions.

CLI

The CLI uses the same parser, embedder, and vector store without an MCP client:

npx mcp-local-rag ingest ./docs/
npx mcp-local-rag sync ./docs/
npx mcp-local-rag query "authentication API"
npx mcp-local-rag query "auth" --scope /docs/api --scope /docs/guide
npx mcp-local-rag read-neighbors --file-path /abs/path.md --chunk-index 5
npx mcp-local-rag list
npx mcp-local-rag status
npx mcp-local-rag delete ./docs/old.pdf
npx mcp-local-rag delete --source "https://example.com/docs"

Global options such as --db-path, --cache-dir, and --model-name go before the subcommand. Subcommand options go after it:

npx mcp-local-rag --db-path ./my-db query "authentication"

Run npx mcp-local-rag --help for the complete command reference.

The CLI does not read MCP client configuration. Set the same environment variables or flags if both interfaces should share an index. In particular, MODEL_NAME and the CLI --model-name must match for a shared database.

Search Tuning

Keyword boost is enabled by default. Relevance-gap grouping and the distance and file filters are optional controls for corpora that need tighter result selection.

Variable	Default	Description
RAG_HYBRID_WEIGHT	0.6	Keyword boost factor (0.0–1.0). 0 disables keyword reranking; 1 applies the maximum boost.
RAG_GROUPING	(not set)	similar keeps the first relevance group; related keeps up to two, using significant vector-distance gaps as boundaries.
RAG_MAX_DISTANCE	(not set)	Filter out low-relevance results (e.g., 0.5).
RAG_MAX_FILES	(not set)	Limit results to top N files (e.g., 1 for single best file).

For API specifications and other documents containing many identifiers, a stronger keyword weight can improve exact-term ranking:

"env": {
  "RAG_HYBRID_WEIGHT": "0.7"
}

• 0.7: slightly stronger exact-term reranking than the default
• 1.0: maximum keyword boost

How It Works

During ingestion:

1. The parser extracts text for the input format.
2. The semantic chunker finds topic boundaries and preserves Markdown code blocks.
3. Transformers.js creates embeddings locally.
4. LanceDB stores the chunks, metadata, vectors, and full-text index.

During search:

1. The query is embedded with the same model.
2. Vector search retrieves semantically related chunks.
3. Optional distance and relevance-group filters narrow the candidates when configured.
4. Full-text matches boost exact query terms.

Agent Skills

Agent Skills provide query and ingestion guidance for AI assistants:

npx mcp-local-rag skills install --claude-code
npx mcp-local-rag skills install --claude-code --global
npx mcp-local-rag skills install --codex

Installed skills cover query formulation, result refinement, and HTML ingestion. Ask the assistant to use the mcp-local-rag skill explicitly if it does not activate automatically.

Configuration

The MCP server reads environment variables. The CLI accepts the same variables plus the listed flags, with CLI flags taking precedence.

Environment Variable	CLI Flag	Default	Description
BASE_DIR	--base-dir	Current directory	One document root; the CLI flag is repeatable on ingest, list, and sync
BASE_DIRS	N/A	(unset)	JSON array of document roots; takes precedence over BASE_DIR
DB_PATH	--db-path	./lancedb/	Vector database location
CACHE_DIR	--cache-dir	./models/	Model cache directory
MODEL_NAME	--model-name	Xenova/all-MiniLM-L6-v2	Hugging Face embedding model
MAX_FILE_SIZE	--max-file-size	104857600 (100MB)	Maximum file size in bytes
CHUNK_MIN_LENGTH	--chunk-min-length	50	Minimum chunk length in characters (1–10000)
RAG_DEVICE	N/A	cpu	ONNX Runtime execution device
RAG_DTYPE	N/A	fp32	Embedding dtype passed to the selected model

Document Roots (BASE_DIR and BASE_DIRS)

mcp-local-rag only allows file operations inside configured roots. For multiple roots, BASE_DIRS must be a JSON array of non-empty paths:

export BASE_DIRS='["/Users/me/Documents/work","/Users/me/Projects/specs"]'

Root configuration is resolved in this order:

1. CLI --base-dir <path> flags (repeatable on ingest, list, and sync)
2. BASE_DIRS
3. BASE_DIR
4. Current directory

Each source replaces the lower-priority source rather than merging with it. Invalid BASE_DIRS configuration fails instead of falling back to BASE_DIR or the current directory. status remains available in MCP so the client can report the configuration error.

npx mcp-local-rag ingest --base-dir /Users/me/work --base-dir /Users/me/specs /Users/me/work/readme.md
npx mcp-local-rag list --base-dir /Users/me/work --base-dir /Users/me/specs
npx mcp-local-rag sync --base-dir /Users/me/work --base-dir /Users/me/specs
BASE_DIRS='["/Users/me/work","/Users/me/specs"]' npx mcp-local-rag list

Storage and Models

DB_PATH and CACHE_DIR are relative to the process working directory by default. Set absolute paths when the MCP client may start the server from different project directories.

Set MODEL_NAME or pass --model-name to choose a Hugging Face embedding model that fits the language and domain of your documents.

mcp-local-rag generates embeddings with mean pooling and L2 normalization. When choosing a model, check whether these settings match its recommended inference setup, since the pooling method can affect retrieval quality.

Changing MODEL_NAME, RAG_DEVICE, or RAG_DTYPE can make existing vectors incompatible. Use a new DB_PATH or delete the existing index and re-ingest after changing the embedding configuration.

An example model for English documents is Xenova/bge-small-en-v1.5.

Security and Operation

• File access is restricted to BASE_DIR, BASE_DIRS, or CLI --base-dir roots.
• Symlinks that resolve outside every configured root are rejected.
• Document processing and search make no network requests after the required models are cached.
• The server is designed for one local user and does not provide authentication or access control.
• Do not run multiple CLI or MCP writers against the same DB_PATH. Read-only queries can run while a sync is active.
• Back up an index by copying its DB_PATH directory while no writer is active.

<details> <summary><strong>Troubleshooting</strong></summary>

"No results found"

Documents must be ingested first. Run "List all ingested files" to verify.

Model download failed

Check internet connection. If behind a proxy, configure network settings. The model can also be downloaded manually.

"File too large"

Default limit is 100MB. Split large files or increase MAX_FILE_SIZE.

Slow queries

Check chunk count with status. Large documents with many chunks may slow queries. Consider splitting very large files.

"Path outside BASE_DIR"

Ensure file paths are within one of the configured roots (BASE_DIR, any BASE_DIRS entry, or any CLI --base-dir). Use absolute paths.

"BASE_DIRS must be a JSON array..."

BASE_DIRS accepts a JSON array of one or more non-empty path strings:

• Valid: BASE_DIRS='["/Users/me/work","/Users/me/specs"]'
• Invalid: BASE_DIRS=/a:/b (delimiter syntax not supported)
• Invalid: BASE_DIRS='[]' (empty array)

MCP client doesn't see tools

1. Verify config file syntax
2. Restart client completely (Cmd+Q on Mac for Cursor)
3. Test directly: npx mcp-local-rag should run without errors

</details>

Contributing

Contributions welcome! See CONTRIBUTING.md for setup and guidelines.

License

MIT License. Free for personal and commercial use.

Blog Posts

• Building a Local RAG for Agentic Coding: Technical deep-dive into the semantic chunking and hybrid search design.

Acknowledgments

Built with Model Context Protocol by Anthropic, LanceDB, and Transformers.js.