mcp-secret-scrub

mcp-name: io.github.sudo-ai-git/mcp-secret-scrub

Deterministic, no-LLM MCP server that scrubs secrets from text, logs, and transcripts before they enter agent context — and never leaks the value.

No LLM. No network. Pure structural detection. MIT. Crown-jewel-free.

The problem it solves

Before you hand raw text to an agent (or store it, or pass it to a tool), you often don't know whether it contains a live secret. Platform scrubbers miss patterns all the time — a private key, an nvapi- token, a github_pat_ token, an api_key= assignment mid-log. If that text reaches an LLM context or a persisted transcript, the secret is effectively exfiltrated.

This server answers, deterministically:

Which secrets are in this text, and can you redact them safely before it goes anywhere?

Detection coverage (deterministic profiles)

The scan never returns the secret value — only its type, count, and position. That is a hard safety contract, enforced by test.

Tools (MCP)

Modes:

• redact (default) → [REDACTED:TYPE]
• mask → shows first 4 + last 2 chars
• hash → deterministic SHA-256 prefix (reproducible across calls)

Quick start (stdio)

pip install mcp-secret-scrub
mcp-secret-scrub          # stdio (default)

Or via uv/pipx for an installable console entry:

pipx install mcp-secret-scrub

MCP client config:

{ "mcpServers": {
    "secret-scrub": { "command": "mcp-secret-scrub" }
}}

Streamable HTTP (remote / Smithery-publishable)

python3 mcp_server.py --http --port 8138   # serves on http://<host>:8138/mcp/

Determinism & safety guarantees

• Deterministic: same input → identical output in every mode, every call.
• Never leaks: scan_text and scrub_text never emit the original token; _deterministic_hash is SHA-256 (no salt) so output is reproducible.
• No LLM, no network: pure regex + reachable structure detection.
• Input-safe: non-string input returns a clean error, not a traceback.

Verification

• python3 test_detector.py — 14/14 core checks (detection, redaction, determinism, no-leak contract, benign/unicode/empty input, bad-mode)
• python3 test_e2e.py — drives the real MCP stdio transport and asserts the secret does NOT cross the wire

License & provenance

MIT. Part of the sudo-ai-git deterministic no-LLM agent-trust MCP family (mcp-skill-sec · mcp-verify-claim · mcp-benchmark-hygiene · mcp-secret-scrub).