MCP Vector Proxy

A semantic MCP proxy that sits between AI agents and MCP Router, exposing only 4 tools instead of hundreds. Uses local vector embeddings to find the right tool on demand — no OpenAI key required.

Why

When you have 150+ MCP tools, passing all of them to an AI agent costs ~30,000 tokens per request. This proxy exposes just 4 tools (discover_tools, execute_tool, batch_execute, refresh_tools). The agent searches semantically for what it needs, then calls it — reducing token usage by ~93%.

Without proxy:  151 tools × ~200 tokens = 30,860 tokens per request
With proxy:     4 tool definitions + search results = ~500 tokens

Related MCP server: ToolsDNS

Platform Support

Prebuilt binaries are downloaded automatically at npm install via scripts/fetch-tray.js. To build from source: npm run build:tray.

Cross-compiling the tray binary

The Rust tray (tray-rs/) compiles to 6 platform/arch combos. Each combo is a separate binary in dist/tray/:

mcp-tray-win-x64.exe
mcp-tray-win-arm64.exe
mcp-tray-macos-x64
mcp-tray-macos-arm64
mcp-tray-linux-x64
mcp-tray-linux-arm64

Build for current platform

npm run build:tray      # or:
cd tray-rs && cargo build --release

Cross-compile to another target

# Add the target once
rustup target add aarch64-pc-windows-msvc

# Build
cd tray-rs
cargo build --release --target aarch64-pc-windows-msvc

# Stage the binary
cp target/aarch64-pc-windows-msvc/release/mcp-tray.exe ../dist/tray/mcp-tray-win-arm64.exe

Common targets:

• x86_64-pc-windows-msvc (Windows x64)

• aarch64-pc-windows-msvc (Windows ARM64)

• x86_64-apple-darwin (macOS Intel)

• aarch64-apple-darwin (macOS Apple Silicon)

• x86_64-unknown-linux-gnu (Linux x64)

• aarch64-unknown-linux-gnu (Linux ARM64, requires gcc-aarch64-linux-gnu)

CI builds

Push to main triggers .github/workflows/build-tray.yml which builds all 6 binaries and uploads them as artifacts. Tagging a release (git tag v0.2.0 && git push --tags) attaches them to a GitHub Release, which npm install then downloads via the postinstall hook.

Architecture

MCP Router (all your servers)
        │ stdio
        ▼
mcp-vector-proxy  (tray-managed background process, port 3456)
  - Local embeddings: mxbai-embed-xsmall-v1 q8 (~23MB, runs offline)
  - sqlite-vec persistence (native KNN vector search via vec0 virtual table)
  - Hybrid search: dense vector (sqlite-vec KNN) + BM25 keyword + RRF fusion
  - Auto-syncs when tools change (MCP notifications + polling)
  - HTML dashboard at / + JSON /health
  - HTTP: Streamable HTTP only (SSE dropped — no known client used it)
        │
        ├── Claude Code / other agents  (HTTP → :3456/mcp)
        │
        └── Claude Desktop              (stdio-bridge → HTTP)

System tray  (node dist/tray.js, auto-starts on login)
  - Green  = connected, N tools indexed
  - Yellow = MCP Router reconnecting (cache still serves discover_tools)
  - Red    = proxy down / crashed (auto-restarts)
  - Right-click → Open Dashboard / Open Log File / Restart Proxy / Exit
  - Proxy logs to ~/.mcp-proxy/proxy.log

Requirements

• All platforms: Node.js 18+, MCP Router installed and running

• Windows: Windows 10/11

• macOS: macOS 10.15+

• Linux: Any desktop with a system tray (GNOME, KDE, etc.)

First run: mxbai-embed-xsmall-v1 (~23MB) downloads automatically on first startup and is cached to .model-cache/. Subsequent starts are instant.

Setup

1. Configure your token

cp .env.example .env
# Edit .env and replace "your-mcp-router-token-here" with your real MCPR_TOKEN

The .env file is gitignored. Alternatively, set MCPR_TOKEN as a system environment variable — it takes precedence over the .env file.

2. Install dependencies and build

npm install
npm run build

3. Register auto-start and launch the tray

Windows:

npm run setup
# or: powershell -ExecutionPolicy Bypass -File setup.ps1

macOS / Linux:

npm run setup
# or: bash setup.sh

This registers the tray to start on every login and launches it immediately.

4. Connect your AI clients

Claude Code (~/.claude.json):

{
  "mcpServers": {
    "mcp-vector-proxy": {
      "type": "http",
      "url": "http://127.0.0.1:3456/mcp"
    }
  }
}

Claude Desktop (%APPDATA%\Claude\claude_desktop_config.json on Windows, ~/Library/Application Support/Claude/claude_desktop_config.json on macOS):

{
  "mcpServers": {
    "mcp-vector-proxy": {
      "command": "node",
      "args": ["/absolute/path/to/mcp-proxy/dist/stdio-bridge.js"],
      "env": { "PROXY_URL": "http://127.0.0.1:3456/mcp" }
    }
  }
}

Any other agent — point it at http://127.0.0.1:3456/mcp (Streamable HTTP).

Environment Variables

Tool Allow/Deny Lists

Scope what the proxy exposes to agents. Patterns are JavaScript regex matched against tool names. Comma-separated.

# Only expose GitHub and Slack tools
ALLOW_TOOLS=^github_.*,^slack_.*

# Hide anything destructive plus the admin tools
DENY_TOOLS=.*_delete_.*,^admin_.*

# Lock down to a single specific tool
ALLOW_TOOLS=^gmail_send_email$

Enforcement is layered:

1. Index time — denied tools are never embedded, never appear in discover_tools results

2. Execute time — execute_tool and batch_execute refuse denied tools with a clear error, even if the agent learned the name out-of-band

3. Fingerprint — computed on the filtered list, so changes to filtered-out tools don't trigger re-indexing

When active, the dashboard shows a yellow banner with the patterns. Changes require a proxy restart.

Tools Exposed to Agents

npm Scripts

npm run build          # Compile TypeScript → dist/
npm run setup          # Register auto-start + launch tray (platform-detected)
npm run update         # Build + restart tray (platform-detected)

Updating

After changing source code:

npm run update

This rebuilds everything and restarts the tray (which restarts the proxy).

Health Check

GET http://127.0.0.1:3456/health

{
  "status": "ok",
  "routerConnected": true,
  "tools": 151,
  "indexedAt": "2026-02-17T15:51:21.620Z",
  "lastError": null,
  "sessions": { "streamable": 1 }
}

Status is "ok" when MCP Router is connected and tools are indexed. "disconnected" means the proxy is up but MCP Router is unreachable — discover_tools still works from cache, execute_tool will fail until reconnection.

Dashboard

Open http://127.0.0.1:3456/ in a browser (or use the tray's Open Dashboard menu item) for:

• Live status card (connection, tool count, indexedAt, sessions)

• Search playground — type a query, see ranked results with relevance bars and argument schemas

• Tool browser — searchable list of all indexed tools with click-to-copy names

• Recent activity — last 20 discover/execute/batch calls with latency, p50/p99 summary

• Refresh button — triggers an immediate re-index

Read-only JSON helpers (used by the dashboard, also useful for scripting):

• GET /discover?q=<query>&limit=<n> — same ranking as discover_tools

• GET /tools — all indexed tools as JSON

• POST /refresh — trigger re-index

Log File

The tray pipes the proxy child's stdout/stderr to ~/.mcp-proxy/proxy.log. Use the tray's Open Log File menu item or:

# Follow live
tail -f ~/.mcp-proxy/proxy.log        # macOS/Linux
Get-Content ~\.mcp-proxy\proxy.log -Wait   # Windows PowerShell

This is the first place to look when the proxy "didn't start on boot".

File Reference

src/
  index.ts          — Main proxy server (HTTP + stdio modes, mounts dashboard)
  server.ts         — MCP tool handlers (discover / execute / batch / refresh)
  dashboard.ts      — HTML dashboard + /discover + /tools read-only routes
  vector-index.ts   — Embeddings + sqlite-vec KNN search + BM25 + RRF
  search.ts         — Pure BM25 / RRF functions
  filter.ts         — Tool allow/deny regex filter (3-layer enforcement)
  stats.ts          — Per-tool stats (call count, success rate, latency)
  activity.ts       — Recent activity ring buffer
  router-connection.ts — MCP Router child lifecycle, reconnection, polling
  launch-router.ts  — Spawns MCP Router CLI (offline after first install)
  tray.ts           — Spawns Rust tray binary, JSON-lines IPC
  config.ts         — Env loading + typed constants

tray-rs/            — Rust crate using tray-icon (cross-platform native tray)
scripts/fetch-tray.js — Postinstall: downloads prebuilt binary from GitHub
build-tray.ps1 / .sh — Build Rust tray for current platform

dist/               — Compiled output (generated by npm run build)

.env.example        — Template for .env (copy and fill in MCPR_TOKEN)
.env                — Your config (gitignored, never commit this)

setup.ps1           — Windows: install CLI locally + register auto-start + launch tray
setup.sh            — macOS/Linux: same
restart-tray.ps1    — Windows: kill + restart tray
restart-tray.sh     — macOS/Linux: same

.lancedb/           — Legacy LanceDB persistence (no longer used, safe to delete)
.sqlite-vec/        — SQLite + sqlite-vec persistence (auto-generated, gitignored)
.tool-meta.json     — Tool fingerprint cache (auto-generated, gitignored)
.model-cache/       — Downloaded embedding model (~23MB, gitignored)
~/.mcp-proxy/proxy.log — Runtime log written by tray (rotated manually)

How Tool Sync Works

1. On startup, tools from MCP Router are embedded using mxbai-embed-xsmall-v1 and stored in SQLite (DB_PATH)

2. MCP Router sends a tools/list_changed notification when servers change → immediate re-index

3. A polling fallback runs every 15s to catch any missed notifications

4. Re-indexing is incremental — only new or changed tools get re-embedded, cached embeddings are reused

5. Tool schema changes (new parameters) are detected via fingerprint and trigger re-indexing

6. If MCP Router is unreachable, discover_tools still serves from the in-memory cache; only execute_tool requires a live router

How Search Works

discover_tools uses hybrid search for best accuracy:

1. Dense vector search — sqlite-vec KNN over mxbai-embed-xsmall-v1 embeddings (handles paraphrasing, synonyms, conceptual matches; sublinear via HNSW scan)

2. BM25 keyword search — in-memory scoring over tool names + descriptions finds exact keyword matches that semantic search can miss

3. RRF fusion — Reciprocal Rank Fusion merges both ranked lists into a single optimal ranking

Embeddings live in the tools vec0 virtual table alongside their metadata. Vector distance from sqlite-vec is converted to cosine similarity (1 − distance for L2-normalized vectors).

This combination handles both vague queries ("something to do with files") and precise queries ("browser_screenshot") accurately.

Migrating from LanceDB

If you're upgrading from a pre-sqlite-vec version:

1. The old .lancedb/ directory is ignored (no longer in deps)

2. On first startup with the new code, all tools are re-embedded from scratch

3. One-time cost: ~5-25s depending on tool count (165 tools ≈ ~10s on typical hardware)

4. After successful re-index, you can delete .lancedb/ manually

Fingerprint matches won't be honored on first run because the new DB is empty — reindexing is forced.