4da MCP Server

@4da/mcp-server

Upgrade intelligence for AI coding agents. Before your agent bumps a dependency it learns what changes between the version you run and the one you want, which of your files that touches, and which vulnerabilities the move fixes, from your own lockfiles, on your machine. Plus vulnerability scanning at osv-scanner parity, ranked upgrade plans and decision memory. Zero config, no account.

You:     "Upgrade axum to 0.8"
Agent →  upgrade_impact { package: "axum", to_version: "0.8.4" }

         axum 0.7.9 -> 0.8.4: 5 releases (0.8.2 yanked), changelog from the 0.8.4 crate.
         12 breaking entries, 8 touch your code (Path, Query, Router, extract, serve):
           breaking  Remove OptionalFromRequestParts impl for `Query`        (you use Query)
           breaking  Require `Sync` for all handlers added to `Router`       (you use Router)
           ...
         Your code: 10 files import axum.

(Real output, abridged, run on this repository, 2026-10-02.)

One command to install. No API keys. No accounts. Your code never leaves your machine.

Install

Requires Node.js 22 or later.

The server uses Node's built-in node:sqlite (Node 22.13 and later), so it needs no install script and works with npm 12's default of blocking them. On Node 22.0-22.12 it uses the optional better-sqlite3, whose native module npm 10 and 11 build on install. npx @4da/mcp-server --doctor shows which one is in use.

claude mcp add 4da -- npx @4da/mcp-server

As a Claude Code plugin (the MCP server plus a hook):

claude plugin marketplace add 4DA-Systems/4da-mcp-server
claude plugin install 4da@4da

The hook: when your agent edits a dependency's version in package.json, Cargo.toml, pyproject.toml, requirements.txt or go.mod, it is told which packages moved and given the exact dependency_check and upgrade_impact calls to make before it installs and builds. The hook is plain Node, contacts nothing, and stays silent for every other edit.

Add to ~/.cursor/mcp.json (Cursor), ~/.codeium/windsurf/mcp_config.json (Windsurf), or ~/.config/devin/mcp_config.json (Devin Desktop and Devin CLI; %APPDATA%devinmcp_config.json on Windows):

{
  "mcpServers": {
    "4da": {
      "command": "npx",
      "args": ["@4da/mcp-server"]
    }
  }
}

Run MCP: Open User Configuration and add the entry, or edit the file directly: %APPDATA%CodeUsermcp.json (Windows), ~/Library/Application Support/Code/User/mcp.json (macOS), ~/.config/Code/User/mcp.json (Linux). VS Code uses servers, not mcpServers:

{
  "servers": {
    "4da": {
      "type": "stdio",
      "command": "npx",
      "args": ["@4da/mcp-server"]
    }
  }
}

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "4da": {
      "command": "npx",
      "args": ["@4da/mcp-server"]
    }
  }
}

npx @4da/mcp-server --setup --dry-run   # show each file and entry, write nothing
npx @4da/mcp-server --setup

Writes Cursor, VS Code (and Insiders), Windsurf, Devin Desktop and Claude Desktop configs it finds, merging into what is there: other servers, settings and comments are kept, a backup (.bak) is written first, and a file it cannot parse is left untouched with the entry to add by hand. For Claude Code it prints the claude mcp add command instead of editing ~/.claude.json.

Then ask your AI: "What changes if I upgrade X to Y?", "Scan for vulnerabilities" or "What should I upgrade first?"

How It Works

The server reads every lockfile of the project it is started in, including independently-locked projects below the root (a repo with src-tauri/Cargo.lock beside a root pnpm-lock.yaml is scanned whole) and skipping what .gitignore excludes: package-lock.json / npm-shrinkwrap.json, pnpm-lock.yaml (v5–v9), yarn.lock (v1 and berry), bun.lock, Cargo.lock (Cargo workspaces included), poetry.lock, uv.lock, pdm.lock, Pipfile.lock, requirements pins (*requirements*.txt, requirements/*.txt, with -r and -c), go.mod / go.sum (Go's build list), Gemfile.lock (RubyGems; git and path gems are local code, not releases) and composer.lock (Packagist). Every Python source in a folder is read, not only the first. Every installed copy is scanned, not one version per name, with the lockfile's own dev flags. It re-reads them whenever a lockfile changes, and for npm it also checks what node_modules actually holds. The walk goes 4 levels down and up to 256 projects; whatever it leaves out, and every manifest with no lockfile (its declared ranges are not installs and are not scanned), is listed in the answer's coverage block, never dropped silently. So are manifests of ecosystems it does not read (Maven pom.xml, Gradle, .NET *.csproj / packages.lock.json, Pub, Hex, SwiftPM, CocoaPods: coverage.not_covered), lockfiles that exist but cannot be read (merge-conflict markers, invalid JSON: coverage.unreadable_lockfiles), and lockfiles under test-fixture directories (tests/, test/, fixtures/, testdata/, __fixtures__/, conformance/ ...), which are not scanned as the project's own unless you pass include_test_fixtures: true (coverage.not_scanned).

An incomplete answer is never a clean one. When OSV.dev cannot answer for some dependencies (outage, HTTP error, timeout, the query budget), vulnerability_scan starts with summary: "NOT CHECKED: ... N of M dependencies have no vulnerability answer", counts them in coverage.unchecked_dependencies, and sets total_vulnerable_packages and by_severity to null (what the checked part found is under found_in_checked_dependencies); dependency_health withholds its score and vulnerable count, and upgrade_planner sets vulnerabilityDataAvailable: false. Large trees are queried in batches of 1,000 as OSV's budget allows, so a tree past 10,000 dependencies is answered in full.

Measured against osv-scanner on 19 public repositories (npm, pnpm v5-v9, yarn v1 and berry, bun, Cargo, Poetry, uv, Pipfile, requirements, Go; 2026-10-10), every difference settled by OSV's own API: precision 1.00 over 19,115 findings, recall 19,115 of 19,116 on the lockfiles it reads (Maven/Gradle are not read). Newly read requirement files were also checked against pip-audit.

• OSV.dev for known vulnerabilities, matched to exact installed versions
• npm registry, crates.io, PyPI, Go module proxy (registry.npmjs.org, crates.io and index.crates.io, pypi.org, proxy.golang.org) for versions, deprecations and yanks
• npm download counts (api.npmjs.org), for dependency_health's weekly-downloads figure
• The package's own registry archive (registry.npmjs.org, static.crates.io, files.pythonhosted.org, proxy.golang.org) for the changelog upgrade_impact reads; GitHub only if you opt in with FOURDA_GITHUB_CHANGELOG=true (below)
• npm full packument, the crates.io versions API, the PyPI JSON API and the Go proxy's version list for dependency_check (publish times, yanks and retractions; on npm and crates.io also publishers, install scripts, per-version dependencies). These requests carry the package name only; the version you have installed is never sent to a registry, except that the Go proxy's list has no dates, so it is asked for the .info of the versions being judged (the same request go get makes). OSV.dev's advisory list for the package lets dependency_check name the safe releases in a constraint. Packuments are cached on disk and revalidated with If-None-Match; crates.io API reads are spaced one per second.
• Hacker News Algolia API (hn.algolia.com), only when you call ecosystem_pulse
• GitHub (api.github.com, raw.githubusercontent.com), only with FOURDA_GITHUB_CHANGELOG=true
• Your embedding provider, only if you configure one for semantic recall (a local Ollama URL, or api.openai.com; see below)

Those are all the hosts the server contacts.

Results are cached (24h for registry data, 1h for vulnerabilities, 30min for news) and rate-limited per source.

What's sent over the network: package names and versions (the same data visible in your lockfile), and, only for ecosystem_pulse, the names of a few of your dependencies as search terms. No source code, no file paths, no personal data. The call-site scan of upgrade_impact runs locally. Set FOURDA_OFFLINE=true to disable all network calls.

GitHub release notes (opt-in, off by default). Many packages ship no changelog in their registry archive (vite, zod, cobra, most Go modules). With FOURDA_GITHUB_CHANGELOG=true in the server's environment, upgrade_impact reads the repository's GitHub releases when the archive has no changelog for the range (for PyPI, first a changelog file the project links on GitHub from its project_urls). GitHub then receives the repository name and the versions, nothing else. It uses the unauthenticated REST API (60 requests an hour) or GITHUB_TOKEN when set (5,000); a rate limit is reported with its reset time, never retried in a loop, and results are cached. With it off, an answer without a changelog says so and names the setting; nothing is guessed.

What's written to disk, and where: only files the server owns, in its folder in your user data directory (%LOCALAPPDATA%\4da-mcp, ~/Library/Application Support/4da-mcp or ~/.local/share/4da-mcp; FOURDA_MCP_HOME moves it): cache.db (registry, OSV and changelog responses; safe to delete) and standalone.db (without the desktop app: your project scan and the decisions, agent memory and feedback you record). Nothing is written inside your repository.

When the 4DA desktop app is installed, the server reads the app's database (4da.db) through a read-only connection and never creates or alters anything in it: no tables, no columns, no cache. The only writes are rows in the four app-owned tables the tools exist to fill, so the app sees them: decisions (decision_memory -> developer_decisions), agent memory (agent_memory), and feedback (record_feedback -> interactions and feedback, which the app's calibration reads). Those go through a separate write connection that waits briefly for the app's lock. If your app version lacks the table or a column a record needs, the record goes to standalone.db instead and the response says so in _meta. (Before 6.1 the server also created a live_cache table inside the app's database; it now keeps that cache in cache.db.)

Where configuration and the database come from: FOURDA_DB_PATH if set (a relative path resolves against the server's working directory and must name an existing file; an absolute path that names no file is created as a new standalone database when its directory exists, and the first tool answer says so in _meta.database_note; otherwise it is refused with an error), else the desktop app's database in its data directory, else the server's own standalone.db. Embedding settings come from FOURDA_SETTINGS_PATH, else the settings.json beside FOURDA_DB_PATH, else the desktop app's data directory. Nothing is picked up from the directory the server is started in: until 6.2.5 a data/settings.json or data/4da.db inside (or beside) the working directory was adopted, so a cloned repository could redirect semantic recall to a host of its choosing or plant "decisions".

The one exception: if you explicitly configure an OpenAI embedding provider (FOURDA_EMBED_PROVIDER=openai) for semantic recall, the decision/memory text you store is sent to OpenAI to be embedded. The default — no embedding provider, or a local Ollama one — keeps everything on your machine, and FOURDA_OFFLINE=true overrides it regardless.

Ecosystems supported: npm, crates.io (Rust), PyPI (Python), Go; vulnerability_scan also reads RubyGems (Gemfile.lock) and Packagist (composer.lock). Maven, Gradle and .NET are not read, and are listed as not covered. upgrade_impact reads npm, crates.io, PyPI and Go. PyPI: versions and dates from the PyPI JSON API, the changelog from the release's sdist, and import sites matched on the module the distribution installs: read from your virtualenv's metadata (.venv, venv, env: top_level.txt or RECORD), else a table of well-known differences (PyYAML -> yaml, Pillow -> PIL), else the distribution name, which the answer then labels an assumption. Go: versions and dates from proxy.golang.org, the changelog from the module zip, and a major version 2+ reported as the module path change it is (github.com/jackc/pgx/v4 -> /v5), with the files that import the old path. dependency_check reads all four too; on PyPI and Go, where the registry exposes no publisher identity or install hooks, those signals say "not applicable".

Known limits, stated plainly: a requirements.txt without a lockfile names only your direct pins, so their transitive dependencies are not scanned (use uv lock, poetry lock or pip-compile). Many packages ship no changelog in their registry archive (fastembed, vite, zod among them); upgrade_impact then says so and gives the release-notes URL instead of guessing. Breaking entries are flagged from the changelog's headings and wording, and every entry carries the heading it sits under (under). Measured on a panel of 40 real upgrades across npm, crates.io, PyPI and Go (1,618 entries, gold from three blind raters with verbatim evidence; the panel and the measurement are in the test suite): on the 20 upgrades held out from rule-making, 95% of entries flagged breaking were breaking (95% CI 89-98%) and about 72% of breaking entries were flagged; Go release notes written as prose are the weakest (about 54% recall). Treat the flags as a pre-sort: read every entry of a major upgrade. Each answer says this in _meta.classification.

What You Can Ask

"What changes if I upgrade axum to 0.8?"      -> upgrade_impact
"Check my dependency health"                  -> dependency_health
"Scan for vulnerabilities"                    -> vulnerability_scan
"Which deps should I upgrade first?"          -> upgrade_planner
"Is it safe to bump axios to 1.14.1?"         -> dependency_check
"Pin ws to a 7.x version"                     -> dependency_check (to: "7.x")
"I'm about to bump fastembed 5 -> 7"          -> what_should_i_know
"What's happening in the ecosystem?"          -> ecosystem_pulse
"What's my tech stack?"                       -> get_context
"Record a decision: we chose Postgres"        -> decision_memory
"Does switching to MySQL align?"              -> check_decision_alignment
"Remember: never use ORM for batch inserts"   -> agent_memory

All 16 Tools

Dependency Security

Intelligence

Decisions & Memory

Identity

* Requires the 4DA desktop app for full data.

Prompt: deps

A user-invoked workflow (shown as a slash command by hosts that surface MCP prompts). It tells the agent to run upgrade_planner, check every proposed bump with dependency_check, apply only proceed items in small batches with the project's own tests after each batch, stop and report every review / avoid / wait / unknown item with its evidence, and re-run vulnerability_scan at the end. Optional argument scope (e.g. security only).

Standalone vs. Full Mode

The MCP server works without the desktop app. It keeps a small local database in your user data folder (%LOCALAPPDATA%\4da-mcp, ~/Library/Application Support/4da-mcp or ~/.local/share/4da-mcp, never inside your repository) and scans your project on every start:

Download 4DA for the full experience.

Transports

stdio (default) -- works with all MCP hosts:

npx @4da/mcp-server

Streamable HTTP -- for remote or multi-client setups:

npx @4da/mcp-server --http --port 4840

The HTTP transport binds to 127.0.0.1 by default and applies a Host-header DNS rebinding guard to every request. Exposing it beyond this machine requires a shared secret:

MCP_AUTH_SECRET=<same value as the relay's JWT_SECRET> \
MCP_ALLOWED_HOSTS=mcp.internal \
  npx @4da/mcp-server --http --host 0.0.0.0

Without MCP_AUTH_SECRET a non-loopback bind is refused at startup. With it, every request must carry a Bearer token whose HMAC-SHA256 signature verifies against that secret, and the token's role is enforced per tool (viewer is read-only; member and admin may write). Put TLS in front of it.

HTTP mode is single-tenant. A token's team_id is verified but not used to separate data: every authenticated client shares one database, one agent memory and one set of decisions, and project_path lets any authenticated client scan any directory on the host the server can read. Run one server per team (or per trust boundary), and only behind clients you would give that access.

CLI Reference

npx @4da/mcp-server              # Start server (stdio)
npx @4da/mcp-server --http       # Start server (Streamable HTTP)
npx @4da/mcp-server --setup      # Auto-configure your editors
npx @4da/mcp-server --doctor     # Verify installation health
npx @4da/mcp-server --version    # Print version

Environment Variables

FAQ

Does this send my code anywhere? No. The server sends package names and versions to public APIs (OSV.dev, npm registry, crates.io, PyPI, Go proxy), downloads the target version's archive from the package's own registry for upgrade_impact (and reads GitHub release notes only if you set FOURDA_GITHUB_CHANGELOG=true), and, only when you call ecosystem_pulse, sends a few dependency names as search terms to HN Algolia. No source code, no file paths, no personal data: the call-site scan runs locally. Set FOURDA_OFFLINE=true to disable all network calls. (The sole exception is opt-in OpenAI embeddings — see the network note above.)

Do I need the 4DA desktop app? No. 11 tools work standalone: upgrade impact, pre-install dependency checks, vulnerability scanning, dependency health, upgrade planning, ecosystem news, pre-task briefings, project context, decision memory, alignment checking, and agent memory. The desktop app is where the same engine runs day to day: one worklist across every project on the machine, a morning Brief of what changed in your stack, and an Upgrade Plan. With it installed, your agent also gets 5 more tools: signals, knowledge gaps, developer news judged against your stack, Developer DNA and feedback.

Which AI tools does this work with? Any tool that supports MCP: Claude Code, Claude Desktop, Cursor, Windsurf, VS Code (Copilot), and any custom MCP client.

Build from Source

git clone https://github.com/4DA-Systems/4da-mcp-server.git
cd 4da-mcp-server
pnpm install
pnpm build
pnpm test    # offline

License

Apache License 2.0 (Apache-2.0). See LICENSE.

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