presidio-hardened-x402-mcp

Pre-payment safety gate for x402 — agents call screen_payment_metadata(...), check_payment_policy(...), and check_payment_replay(...) before signing, catching PII, budget overruns, and duplicate payments before metadata or money leaves the agent host.

Part of the presidio-hardened-* toolkit family. Thin MCP (Model Context Protocol) adapter over the presidio-hardened-x402 library, pinned for parent 0.7.x compatibility (presidio-hardened-x402>=0.7.0,<0.8.0).

Why this exists

x402 agentic payments routinely carry user-supplied free text — descriptions, memos, query-string parameters — straight through to merchants and facilitators. When an LLM agent generates that text, it can include PII the user never intended to share. Once the merchant logs it, retention is their decision, not yours.

This MCP server gives agents a small default-deny gate before payment leaves the agent host. Three tools expose the parent library's stable pre-payment controls: PII redaction, spending policy, and replay detection. They are designed to compose with payment-execution and endpoint-safety MCP servers (x402station, Coinbase x402, Sardis, ...), while newer parent-library surfaces such as evidence-ref@1 verification and the v0.7.0 SLO broker stay in the Python library unless an MCP tool explicitly wraps them later.

Install & configure

Requires Python ≥ 3.10. Distributed on PyPI; recommended invocation via uvx (no global install).

Claude Desktop / Claude Code

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or the equivalent on your platform:

{
  "mcpServers": {
    "presidio-x402": {
      "command": "uvx",
      "args": ["presidio-hardened-x402-mcp"]
    }
  }
}

Cursor / Windsurf / Continue

Same shape — every MCP host accepts command / args / env. See your editor's MCP-server docs for the config-file path.

Environment variables

All optional. Defaults give a zero-config in-process mode with no quota, no network, and no PII storage.

Variable	Purpose	Default
PRESIDIO_X402_MCP_MODE	regex (zero-setup) or nlp (needs [nlp] extra + a spaCy model)	regex
PRESIDIO_X402_MCP_MAX_PER_CALL_USD	Max USD per single payment (policy gate)	unset → no limit
PRESIDIO_X402_MCP_DAILY_LIMIT_USD	Max USD per rolling window (policy gate)	unset → no limit
PRESIDIO_X402_MCP_PER_ENDPOINT_JSON	Per-endpoint cap, e.g. '{"api.foo.com": 5.00}'	unset
PRESIDIO_X402_MCP_WINDOW_SECONDS	Rolling window for the daily limit	86400
PRESIDIO_X402_MCP_AGENT_ID	Label written into audit records	unset
PRESIDIO_X402_MCP_REPLAY_TTL	Fingerprint cache TTL (seconds)	300
PRESIDIO_X402_MCP_REDIS_URL	Use Redis for replay state instead of in-memory	unset
PRESIDIO_X402_MCP_AUDIT_PATH	Append-only JSON-L audit log path; omit to disable	unset
PRESIDIO_X402_MCP_LOG_LEVEL	DEBUG / INFO / WARNING / ERROR	INFO
PRESIDIO_X402_MCP_REMOTE_BASE_URL	Enable HTTP-proxy mode for tool 1 — see Modes	unset
PRESIDIO_X402_MCP_REMOTE_API_KEY	API key for the remote screening service	unset
PRESIDIO_X402_FINGERPRINT_KEY	32-byte hex key for cross-process replay detection	unset (per-process)
PRESIDIO_X402_CHAIN_KEY	32-byte hex key for cross-process audit-chain HMAC	unset (per-process)
PRESIDIO_X402_REQUIRE_FINGERPRINT_KEY	Fail startup if replay key is absent or invalid	unset
PRESIDIO_X402_REQUIRE_CHAIN_KEY	Fail startup if audit-chain key is absent or invalid	unset

Generate cross-process keys with openssl rand -hex 32.

Tools

screen_payment_metadata(resource_url, description, reason, entities?)

Detects and redacts PII in payment metadata. No side effects — safe to call repeatedly.

// Input
{
  "resource_url": "https://api.foo.com/u/jane@example.com",
  "description": "monthly fee for jane@example.com",
  "reason": ""
}

// Output
{
  "redacted_resource_url": "https://api.foo.com/u/<EMAIL_ADDRESS>",
  "redacted_description": "monthly fee for <EMAIL_ADDRESS>",
  "redacted_reason": "",
  "entities_found": [
    { "entity_type": "EMAIL_ADDRESS", "field": "resource_url", "count": 1 },
    { "entity_type": "EMAIL_ADDRESS", "field": "description", "count": 1 }
  ],
  "mode": "in_process"
}

entities (optional list of Presidio entity types) narrows detection to a whitelist. Field-length caps mirror the screening-api wire contract that remains stable through parent 0.7.x: resource_url ≤ 2048, description ≤ 4096, reason ≤ 4096 characters. Oversized inputs raise ValueError.

check_payment_policy(resource_url, amount_usd)

Spending-policy gate. Records the spend on success — call exactly once, immediately before payment. Skipping the actual payment after a successful check inflates the daily-limit ledger until the window rolls over.

// Input
{ "resource_url": "https://api.foo.com/x", "amount_usd": 1.50 }

// Output (allowed)
{ "allowed": true }

// Output (denied — over per-call limit of $5.00)
{ "allowed": false, "reason": "...", "limit_usd": 5.00, "amount_usd": 6.00 }

check_payment_replay(resource_url, pay_to, amount, currency, deadline_seconds)

Duplicate-payment gate via HMAC-SHA256 fingerprint of the canonical fields. Records the fingerprint on success — call exactly once, immediately before payment.

amount is a string to preserve precision. Cross-process detection requires PRESIDIO_X402_FINGERPRINT_KEY (and optionally PRESIDIO_X402_MCP_REDIS_URL); otherwise each MCP server process keeps its own in-memory store.

// Input
{
  "resource_url": "https://api.foo.com/x",
  "pay_to": "0xabc...",
  "amount": "1.50",
  "currency": "USDC",
  "deadline_seconds": 1700000000
}

// Output (first seen)
{ "is_replay": false, "fingerprint": "29aaf60f..." }

// Output (duplicate within TTL)
{ "is_replay": true, "fingerprint": "29aaf60f..." }

Modes

In-process (default). Wraps the local presidio-hardened-x402 library in the same process as the MCP server. No network, no API key, no quota. PII never leaves the agent host. Use this unless you have a specific reason not to.

HTTP-proxy. When both PRESIDIO_X402_MCP_REMOTE_BASE_URL and PRESIDIO_X402_MCP_REMOTE_API_KEY are set, screen_payment_metadata calls /v1/screen on the configured host (e.g. https://screen.presidio-group.eu) for centralized audit. On auth / quota / network failure, returns a structured { "error": "auth_error" | "rate_limit" | "unavailable", "detail": ..., "mode": "remote" } — never silently falls back to in-process. Tools 2 and 3 always stay in-process.

Composability

Designed to slot into agent flows alongside payment-execution and endpoint-safety MCP servers:

agent intent: pay https://api.foo.com/x with 1.50 USDC
    │
    ├─ x402station    preflight(url)            ← is the ENDPOINT safe? (decoys, dead, traps)
    │
    ├─ presidio-x402  screen_payment_metadata   ← is the PAYLOAD safe? (PII)
    ├─ presidio-x402  check_payment_policy      ← within budget?
    ├─ presidio-x402  check_payment_replay      ← not a duplicate?
    │
    └─ pay()

screen_payment_metadata is read-only and safe to interleave anywhere. The policy and replay gates record state on call — sequence them immediately before payment.

Combined snippet: preflight → screen → pay

Endpoint-safety and payload-safety are independent signals — calling both is what you actually want before signing. Configure the two MCP servers side-by-side:

{
  "mcpServers": {
    "x402station":   { "command": "npx", "args": ["-y", "x402station-mcp"],
                       "env": { "AGENT_PRIVATE_KEY": "0x…" } },
    "presidio-x402": { "command": "uvx", "args": ["presidio-hardened-x402-mcp"] }
  }
}

Agent flow before signing a payment (pseudocode — each step is one MCP tool call):

# 1. endpoint safety: is the URL trustworthy? (x402station-mcp)
pf = preflight(url)
if not pf["ok"]:
    abort(reason=pf["warnings"])              # decoy / zombie / dead / price-trap

# 2. payload safety: redact PII before it leaves the host (presidio-x402)
s = screen_payment_metadata(resource_url=url, description=description, reason="")
url, description = s["redacted_resource_url"], s["redacted_description"]

# 3. spend gates: record-on-success, call exactly once each (presidio-x402)
if not check_payment_policy(url, amount_usd)["allowed"]:
    abort(reason="policy")
if check_payment_replay(url, pay_to, amount, currency, deadline_seconds)["is_replay"]:
    abort(reason="replay")

# 4. sign + pay
pay(url, amount, description=description)

The two servers are developed independently, on purpose — keeping the signals uncorrelated is the point. See x402station-mcp for the preflight tool's full output schema and warning catalog.

Notes for developers

• Logs go to stderr (MCP clients capture stderr). stdout is reserved for JSON-RPC frames.
• The package is a thin adapter. All security logic lives in presidio-hardened-x402 — read its docs for the entity-type catalog, policy semantics, evidence-ref verification, SLO broker, and audit-chain details.
• This MCP release intentionally exposes the same three tools as 0.1.1; the compatibility update is dependency and metadata alignment with parent 0.7.x, not a promotion of the full parent SLO/evidence surface into MCP.
• When testing via mcp-inspector --cli, bare numeric --tool-arg amount=1.50 is auto-coerced to a float and rejected by the schema. Real MCP clients send proper JSON types; the tool's amount argument is a string to preserve precision.
• Local dev: uv venv && uv pip install -e ".[dev]" && pytest tests/.

License

MIT. See LICENSE.

Links

• This repo: https://github.com/presidio-v/presidio-hardened-x402-mcp
• Issues: https://github.com/presidio-v/presidio-hardened-x402-mcp/issues
• Parent library: https://github.com/presidio-v/presidio-hardened-x402
• Library on PyPI: https://pypi.org/project/presidio-hardened-x402/
• Requirements: PRESIDIO-REQ.md
• Security policy: SECURITY.md
• MCP spec: https://modelcontextprotocol.io
• x402: https://x402.org

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SDLC

This repository is developed under the Presidio hardened-family SDLC: https://github.com/presidio-v/presidio-hardened-docs/blob/main/sdlc/sdlc-report.md.