pii-mcp

Pattern-based PII scrubbing for MCP servers (regex + checksums). Mask emails, IBANs, cards, BICs, MACs, IPs, coordinates, BSNs, US SSNs, German tax IDs, Dutch BTW-ids, phones, Dutch postcodes, and Dutch license plates in tool results — not NER for person names or full street addresses. Language packs: en, nl, and opt-in de.

Aligned with AP examples of persoonsgegevens where pattern/checksum detection can reach them (contact/financial IDs, online identifiers including IP/MAC, locatiegegevens as coordinates, BSN, kenteken). Names, free-text health data, and full street addresses need NER and are out of scope here.

Install

pip install "pii-mcp[fastmcp]"   # FastMCP >= 3.0.0
# or
pip install pii-mcp              # core only (pure Python, no Rust toolchain)

Optional Rust core

Default installs stay pure Python. To accelerate scrubbing with the shared pii-core crate (PyO3), build the optional extension locally:

pip install -e ".[native]"
maturin develop --release --manifest-path crates/pii-mcp-native/Cargo.toml

When pii_mcp._native is importable, scrub_text / scrub_payload use it. Force the Python path with PII_MCP_BACKEND=python.

Performance (Python vs Rust release)

Medians from scripts/bench_backends.py on macOS arm64 / CPython 3.14.7 (release native build; debug builds are not representative):

python scripts/bench_backends.py

FastMCP

from fastmcp import FastMCP
from pii_mcp.fastmcp import PiiScrubMiddleware

mcp = FastMCP("MyServer")
mcp.add_middleware(PiiScrubMiddleware())  # languages=["en", "nl"] by default
# mcp.add_middleware(PiiScrubMiddleware(languages=["en", "nl", "de"]))

Results only. On scrub failure or oversize, the result is withheld — never forwarded unmasked.

Core

from pii_mcp import scrub_text, scrub_payload

scrub_text("mail ada@example.com")
scrub_payload({"email": "ada@example.com"}, languages=["en"])