secretguard-mcp

An MCP (Model Context Protocol) server that scans a code string for hardcoded secrets — AWS keys, Stripe keys, GitHub tokens, Google API keys, Slack tokens, private key blocks, JWTs, and generic high-entropy credentials — so an AI coding agent (Claude Code, Cursor, Windsurf, ...) can catch a secret before it writes the file or makes the commit, instead of finding out at CI/PR-review time. It exposes exactly one tool, scan_for_secrets, runs entirely locally over stdio, needs no API key, and never returns a raw secret value — every finding comes back redacted.

Why this exists

secret-scan-action already catches these secrets in CI, on every PR. That's necessary but late — by the time it runs, the secret has already been written, committed, and pushed. This project reuses that same detection engine (same rules, same entropy check, same redaction) but puts it in front of the agent as a tool call, so the check can happen at generation time, before the secret ever touches disk or history.

Related MCP server: credential-free

What it does

On a scan_for_secrets call:

1. Splits the input code string into lines.

2. Runs the same two-tier ruleset secret-scan-action uses:

   • Pattern rules (high confidence) — distinctive formats that are near-certain secrets when matched: AWS access key IDs (AKIA...) and contextual secret keys, Stripe live keys (sk_live_, rk_live_), GitHub tokens (ghp_, gho_, github_pat_, ...), Google API keys (AIza...), Slack tokens (xox[baprs]-...), private key blocks (-----BEGIN ... PRIVATE KEY-----), and JWTs.

   • Generic entropy rule — a value assigned to a variable named like secret, token, password/credential, or a *key compound commonly used for real secret material (apiKey, sessionKey, signingKey, clientKey, webhookKey, ...) whose value also has high Shannon entropy (looks random, not like a placeholder or an env-var reference). Deliberately does not match a bare *Key — that would also catch partitionKey, cacheKey, queryKey, and similar non-secret identifiers common in ordinary code.

3. Returns every finding's filename, line, ruleId, description, confidence ("high" | "generic"), and a redacted line — the raw secret value never leaves the process. If nothing is found, it returns a plain "No secrets detected." result.

Example output

Calling scan_for_secrets with:

{
  "code": "const key = \"AKIAIOSFODNN7EXAMPLE\";\nconst greeting = \"hello\";",
  "filename": "src/config.ts"
}

returns:

{
  "findings": [
    {
      "filename": "src/config.ts",
      "line": 1,
      "ruleId": "aws-access-key-id",
      "description": "AWS Access Key ID",
      "confidence": "high",
      "redactedLine": "const key = \"AKIA************MPLE\";"
    }
  ],
  "summary": "Found 1 potential secret (1 high-confidence, 0 needs-review).\n\n- [high] src/config.ts:1 — AWS Access Key ID (aws-access-key-id)\n  const key = \"AKIA************MPLE\";"
}

(The AWS key above is AWS's own public documentation placeholder, not a live credential.) A clean scan — e.g. { "code": "const greeting = \"hello world\";" } — returns { "findings": [], "summary": "No secrets detected." }.

Setup

Not yet published to the npm registry — install directly from GitHub via npx. npm install from a git source runs this package's prepare script automatically, which builds dist/ on the fly, so no separate build step is needed.

Claude Code

Add to your project's .mcp.json (or run claude mcp add):

{
  "mcpServers": {
    "secretguard": {
      "command": "npx",
      "args": ["-y", "github:vladimirbakalov/secretguard-mcp"]
    }
  }
}

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "secretguard": {
      "command": "npx",
      "args": ["-y", "github:vladimirbakalov/secretguard-mcp"]
    }
  }
}

No API key, no account, no config options — restart Claude Code / Claude Desktop and scan_for_secrets is available. The tool description tells the agent to call it before writing code that could contain a credential, and again before a commit or PR — most of the time you won't need to ask for it explicitly.

Cursor / Windsurf

Both read the same command/args shape from their own MCP settings UI or config file — point them at npx -y github:vladimirbakalov/secretguard-mcp the same way.

Once this package is published to npm, the args above can drop to ["-y", "secretguard-mcp"] instead — that's a follow-up, not a blocker.

One-click install (.mcpb)

A prebuilt MCP Bundle is attached to the v0.1.0-mcpb release — download secretguard-mcp-0.1.0.mcpb and open it in Claude Desktop (or any other MCPB-compatible client) for a one-click local install, no npx/Node setup required on the client side. Rebuild it yourself with npm run package:mcpb (see scripts/build-mcpb.sh).

This same .mcpb release asset is what server.json at the repo root points at for the official MCP Registry — publishing there is prepared but not yet done, since it requires a one-time interactive mcp-publisher login github device-flow authorization.

Security notes

• The raw secret value matched by a rule is held in memory only for the duration of a single scan_for_secrets call and is redacted (redactLine/redactSecret) before the tool result is built — it never appears in the returned content, structuredContent, or any log line.

• The server does no network calls of any kind. It reads stdin, writes stdout (MCP stdio transport), and does nothing else.

• Generic-tier findings are ambiguous by nature (config placeholders, hashes, and UUIDs can trip the entropy check) — that's expected. Treat confidence: "generic" as "worth a second look," not "confirmed."

Development

npm install
npm run typecheck   # tsc --noEmit
npm test            # vitest run
npm run build       # tsc -p tsconfig.build.json -> dist/

dist/ is not committed — it's built from src/ via the prepare script, which runs both on a git-based npx/npm install and before any future npm publish.

Scope (v1)

One tool, one job: scan a code string, return redacted findings. No allowlist file, no AI triage step, no config options, no persistent state. If this needs any of that later, it'll get added once real usage shows it's needed — not before.

Relationship to secret-scan-action

secretguard-mcp and secret-scan-action share the same detection engine (rules.ts, redact.ts, and the core of scan.ts) but are independent, separately distributed packages: one is a GitHub Action that scans PR diffs in CI, the other is an MCP server that scans arbitrary code strings locally, before a commit exists. Fixing a false positive/negative in the ruleset means updating both.

License

MIT.