Vector Memory MCP Server for GitHub Copilot CLI

An MCP server that adds persistent long-term memory to GitHub Copilot CLI via local semantic vector search. Copilot can recall past conversations, code changes, and decisions across all sessions — by meaning, not just keywords.

Note: This is a community project and is not affiliated with or endorsed by GitHub. GitHub Copilot CLI is a product of GitHub / Microsoft.

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Installation

Prerequisites

You need Node.js ≥18 installed. This gives you node, npm, and npx.

• Windows: winget install OpenJS.NodeJS.LTS
• macOS: brew install node or download from nodejs.org
• Linux: Use your package manager or nodejs.org

That's it. The native SQLite modules (better-sqlite3, sqlite-vec) ship prebuilt binaries for Windows (x64), macOS (x64, ARM), and Linux (x64, ARM) — no compiler or build tools needed.

<details><summary>Build tools only needed if prebuilds aren't available for your platform</summary>

If you're on an unusual platform and the prebuilt binaries aren't available, better-sqlite3 falls back to compiling from source. In that case you'll need:

• Windows: Visual Studio Build Tools with the "Desktop development with C++" workload
• macOS: xcode-select --install
• Linux: sudo apt install build-essential python3 (or equivalent)

</details>

Step 1: Find (or create) your MCP config file

GitHub Copilot CLI reads MCP server definitions from a JSON config file. The user-level config lives at:

OS	Path
Windows	%USERPROFILE%\.copilot\mcp-config.json (e.g. C:\Users\YourName\.copilot\mcp-config.json)
macOS / Linux	~/.copilot/mcp-config.json

If this file doesn't exist yet, create it. If the .copilot folder doesn't exist either, create that too — Copilot CLI will use it.

You can also place a project-level config at .copilot/mcp-config.json in any repo root, but user-level is recommended for this server since it provides memory across all projects.

Step 2: Add the vector-memory server

If the file doesn't exist or is empty, create it with this content:

{
  "mcpServers": {
    "vector-memory": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "ghcp-cli-vector-memory-mcp"]
    }
  }
}

If you already have an mcp-config.json with other servers, add the "vector-memory" entry inside the existing "mcpServers" object:

{
  "mcpServers": {
    "your-existing-server": { "...": "..." },
    "vector-memory": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "ghcp-cli-vector-memory-mcp"]
    }
  }
}

You do not need to clone this repo or run npm install yourself. The npx -y command automatically downloads, installs, and runs the package from the npm registry. It caches the package locally so subsequent launches are fast.

Step 3: Load the server

Close any running Copilot CLI session and start a new one — or if you already have a session open, type /mcp reload to pick up the new config without restarting. The MCP server will launch automatically in the background.

[!IMPORTANT] The very first launch takes a few minutes. On first run, npx installs the package and its native dependencies, then the server downloads a small machine learning model (~34 MB, Xenova/gte-small). This is a one-time cost — subsequent starts are near-instant.

The MCP proxy connects immediately and won't block Copilot CLI from starting. If you try to use vector search before the model is ready, it will tell you it's still warming up.

[!NOTE] Runs comfortably on any laptop. The ONNX embedding model is tiny (~34 MB in memory) and inference is fast even on CPU. There is no GPU requirement. You will not notice any impact on battery life or system performance. The server also idles down and exits automatically after 5 minutes of inactivity, so it costs zero resources when you're not using Copilot.

Step 4: Verify it's working

In a new Copilot CLI session, ask:

Do you have vector search available?

Copilot should confirm it has the vector_search and vector_reindex tools. If it's the first launch and the model is still downloading, it will tell you — just wait a minute and try again.

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What it does

Once installed, Copilot CLI gains two new tools:

Tool	Description
vector_search	Semantic search across all past session history. Find conversations, code changes, and decisions by meaning — not just keywords. Returns ranked results with similarity scores.
vector_reindex	Force a full rebuild of the vector index. Normally not needed — search auto-indexes new content. Use if the index seems stale.

Copilot will use vector_search automatically when it needs to recall past context. You can also prompt it directly: "search your memory for..." or "do you remember when we..."

Data flow

1. Copilot CLI writes session data to ~/.copilot/session-store.db (this already exists)
2. vector-memory reads from that DB (read-only) and creates embeddings
3. Embeddings are stored in ~/.copilot/vector-index.db
4. Indexing triggers: on startup, on each search (if new content exists), and every 15 minutes

All data stays local. Nothing is sent to any external service.

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Configuration

Environment variables

Variable	Default	Description
VECTOR_MEMORY_PORT	(auto)	HTTP port for the singleton server. A deterministic port is computed from your OS username (FNV-1a hash, range 31337–35432). Only set this if two users collide.
VECTOR_MEMORY_IDLE_TIMEOUT	5	Minutes of inactivity before the server shuts down. 0 or negative = never shut down.

Set these in the env block of your config (only if needed):

{
  "mcpServers": {
    "vector-memory": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "ghcp-cli-vector-memory-mcp"],
      "env": {
        "VECTOR_MEMORY_IDLE_TIMEOUT": "10"
      }
    }
  }
}

Multi-user setup

On a shared machine, each user's server runs on a unique auto-assigned port. No extra config needed — just use the same mcp-config.json entry above and each user gets their own singleton server, vector index, and session history.

In the rare case of a port hash collision, the server detects it at startup and tells the affected user to set VECTOR_MEMORY_PORT manually.

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Architecture

copilot.exe ──STDIO──▶ index.js (proxy) ──HTTP──▶ vector-memory-server.js (singleton)
                                                          │
                                                   embed-worker.js (worker thread)
                                                          │
                                                   Xenova/gte-small (ONNX, 34MB)

• index.js — Thin STDIO MCP proxy. One per copilot instance. Checks if the HTTP server is running, launches it if not, then ferries tool calls over HTTP.
• vector-memory-server.js — Singleton HTTP server. Owns the embedding model (one copy in memory), SQLite vector DB, and background indexing. Port is auto-assigned per user via a deterministic hash of the username.
• embed-worker.js — Worker thread that loads the ONNX model and handles embedding inference off the main thread.
• lib.js — Pure logic extracted for testability: filtering, dedup, post-processing, process detection.

Key design decisions

• Singleton: Only one server runs regardless of how many copilot instances are open. Saves ~200MB RAM per additional instance.
• Race condition hardened: EADDRINUSE detection with full diagnostics — distinguishes between healthy singleton, zombie process, and foreign port conflict.
• No duplicates: UNIQUE constraint + INSERT OR IGNORE + isIndexing guard prevents duplicate embeddings even under concurrent access.
• Lazy init: ONNX model only loads after winning the singleton race. Losers exit in about 500ms.
• Idle shutdown: Server exits after 5 minutes of inactivity (no requests and no new session content). The proxy re-launches it on next use.
• Self-healing: Detects and deletes corrupt/truncated model files, re-downloads automatically. Retries with backoff for Windows Defender file locks.

Development

Scripts

npm run lint     # ESLint on all source files
npm test         # 44 unit tests with 100% coverage (node:test, zero external deps)
npm run check    # lint + test

Running tests

npm test

With coverage:

npm test   # coverage is enforced at 100% by default

File overview

File	Purpose
index.js	STDIO MCP proxy — what copilot.exe launches via npx
vector-memory-server.js	HTTP singleton — owns model, DB, indexing
embed-worker.js	Worker thread for ONNX embedding inference
lib.js	Pure logic: filtering, dedup, scoring, handler factory
test.js	44 unit tests with DI mocks, 100% coverage enforced
eslint.config.js	Lint config

Manual server management

# Start server directly (normally done by the proxy)
node vector-memory-server.js

# Check if running (port varies per user — see startup log)
curl -X POST http://127.0.0.1:<PORT>/ping -d "{}"

# Search directly
curl -X POST http://127.0.0.1:<PORT>/search \
  -H "Content-Type: application/json" \
  -d '{"query":"what did I work on yesterday","limit":5}'

# Kill server (find PID first)
cat ~/.copilot/vector-memory.pid

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Troubleshooting

First run is slow

This is expected! On first launch, the server needs to:

1. Install native SQLite extensions (better-sqlite3, sqlite-vec)
2. Download the embedding model (~34 MB from Hugging Face)

This can take 2–5 minutes depending on your connection speed and whether native compilation is needed. Subsequent launches start in seconds.

Port collision with another user

Error: Port 31796 is owned by user "X" (expected "Y")

Two usernames hashed to the same port (rare). One user needs to set a manual override:

{
  "mcpServers": {
    "vector-memory": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "ghcp-cli-vector-memory-mcp"],
      "env": {
        "VECTOR_MEMORY_PORT": "31338"
      }
    }
  }
}

Port occupied by another service

Error: Vector memory server failed to start — port XXXXX may be in use by another service

Something else is listening on your auto-assigned port. Pick a different port using the VECTOR_MEMORY_PORT env var as above.

To check what's on the port:

# Windows
netstat -ano | findstr :31337

# macOS/Linux
lsof -i :31337

Version mismatch

Warning: server version X ≠ proxy version Y

An older server is still running from before an update. Kill it and let the proxy spawn a fresh one:

# Find and kill the server
cat ~/.copilot/vector-memory.pid   # get the PID
kill <PID>                          # or Stop-Process -Id <PID> on Windows

The next copilot launch will start the updated server automatically.

Session store not found

Error: Session store not found

The file ~/.copilot/session-store.db doesn't exist yet. This is normal on a fresh Copilot CLI install — it creates the file after your first conversation. Use Copilot for a bit, then try again.

Embedding model corrupt

Symptom: Server starts but search returns no results or errors.

The ONNX model file may be corrupt (e.g., interrupted download). The server self-heals on restart — kill the server and let it re-launch:

cat ~/.copilot/vector-memory.pid
kill <PID>

If it persists, clear the model cache:

rm -rf node_modules/@huggingface/transformers/.cache

The model will re-download on next launch.

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License

MIT — see LICENSE.