db-gateway

@guardbee/mcp-db-gateway

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A KVKK / GDPR-compliant MCP (Model Context Protocol) server — adds a security layer between an LLM and a database.

Instead of querying your database directly, Claude (or any other LLM) goes through this gateway. Sensitive fields are masked automatically, table access is role-controlled, and every query is written to an audit log.

Telemetry is off by default. With GUARDBEE_TELEMETRY=1 it sends the server, tool, success, duration and short parameter values such as a file path; longer strings and fields like content, token or password are replaced with a placeholder. See @guardbee/mcp-telemetry.

Claude ──► MCP Gateway ──► Database
              │
              ├─ PII masking     (tcKimlik → [REDACTED])
              ├─ Role check      (ai-agent can only reach the products table)
              ├─ Rate limiting   (max 100 queries/minute)
              └─ Audit log       (every query is recorded)

---

Features

• PII Masking — Turkish national ID, IBAN, email, phone, password hashes, etc. are masked automatically
• Role-Based Access (RBAC) — Per-role table allow/deny lists and field rules
• Rate Limiting — Global and per-table request windows
• Audit Log — Writable to console, a file, or an HTTP webhook
• Prisma / Postgres / MySQL / SQLite / MongoDB Adapters — Plug in an existing PrismaClient, a pg Pool, a mysql2 Pool, a better-sqlite3 Database, or a MongoDB Db directly
• Write Support (optional) — insert/update/delete, off by default; gated by per-table + per-role permission, protected-field guarding, and a "don't touch the whole table" safety net
• 195 unit tests — masking, the pipeline, RBAC, the rate limiter, the audit log, and every adapter (read + write) are covered

---

Recent Changes (2026-09-15)

Three new steps in this package's AI Gateway growth work:

1. The query_audit_log tool

Previously the gateway's audit log was write-only — it landed in one of the console/file/http sinks, but Claude itself had no way to look back and ask "what just happened, which calls got denied." Now it can:

// Tool called from the Claude side:
query_audit_log({ table: "orders", deniedOnly: true, limit: 20 })

• How it works: AuditLogger gained an always-on, in-memory ring buffer that's completely independent of the configured sink (audit.bufferSize, default 200). Even when the sink is "http" (a fire-and-forget webhook), history is still queryable through this buffer. The buffer resets when the process restarts, and is never populated while audit.enabled: false.
• Filters: table, tool (the MCP tool name, e.g. "delete_row"), operation (read/insert/update/delete), deniedOnly (denied calls only), since (an ISO 8601 timestamp), limit (default 50, max 200). Results come back newest-first.
• A real bug fixed along the way: registerDbTools (read tools) and registerWriteTools (write tools) previously each built their own GatewayPipeline/AuditLogger instance. That meant audit events from insert_row/update_row/delete_row calls would never have appeared in the buffer that query_audit_log reads — there were two separate, unaware-of-each-other buffers. server.ts now builds a single GatewayPipeline instance and shares it across both tool groups.
• Tests: src/__tests__/audit-logger.test.ts (10 tests — buffer capping, every filter, ring-buffer behavior) plus 3 tests added to pipeline.test.ts (verifying that reads and writes land in the same buffer, that deniedOnly + table filters compose correctly, and that the buffer stays empty while audit.enabled: false).

2. The SQLite adapter

The gateway now works with better-sqlite3 alongside Prisma/Postgres/MySQL:

import Database from "better-sqlite3";
import { createServer, createSqliteAdapter } from "@guardbee/mcp-db-gateway";

const db = new Database("./app.db");
const server = createServer({}, createSqliteAdapter(db));

• Same security pattern as pg/mysql: table/column names can't be parameterized, so they're validated before being embedded in SQL — here using SQLite's PRAGMA table_info(table) instead of information_schema. A name that fails the format check (e.g. users"; DROP TABLE users;--) or isn't in the live schema is rejected before any query reaches SQLite.
• better-sqlite3 is only an optional peerDependency — it was not added to the package's own devDependencies, since it requires a native binding; tests (like the pg/mysql tests) were written against a simple mock object matching the SqliteQueryable interface, without importing the real package.
• lastInsertRowid instead of RETURNING for insert: since SQLite's RETURNING support is version-dependent, this follows the same approach as the MySQL adapter's insertId — if the table has an id column and it's not already in data, the inserted row gets lastInsertRowid attached.
• Bonus fix: the AuditEvent/AuditQueryFilter types were not exported from the package root (index.ts) at all — added for consumers who want to type their own calls to GatewayPipeline.queryAuditLog().
• Tests: src/__tests__/sqlite-adapter.test.ts (21 tests) — the same scenario set as pg-adapter.test.ts: table listing, filtered/unfiltered queries, limits, unknown table/column rejection, injection-attempt rejection, insert (including id assignment), update, delete.

3. The MongoDB adapter

The gateway now also works with a Db instance from the mongodb driver:

import { MongoClient } from "mongodb";
import { createServer, createMongoAdapter } from "@guardbee/mcp-db-gateway";

const client = new MongoClient(process.env.DATABASE_URL!);
await client.connect();
const server = createServer({}, createMongoAdapter(client.db("mydb")));

• A different risk class — not SQL injection, but operator injection: for pg/mysql/sqlite the risk was a table/column name being embedded in SQL. MongoDB never embeds identifiers, but if a key in filter/data is a Mongo operator like $where/$ne, or a value is an operator object like { $ne: null }, the "simple key-value equality filter" a tool declares can silently turn into an arbitrary query. This adapter rejects all of the following up front:
  • any key starting with $ (in both filter and data)
  • any key containing . — a dotted path (e.g. "passwordHash.reset") is both an operator-like risk and a way to bypass findProtectedWriteFields's exact-name matching (outside of its glob support)
  • any non-scalar (object/array) filter value — including an operator-object bypass attempt like { status: { $ne: "active" } }
• mongodb is only an optional peerDependency — same as the SQLite adapter, tests were written against a mock object matching the MongoDatabase interface, without importing the real package.
• "Table" = collection. tables() maps to listCollections(); insert attaches _id (the driver's insertedId) to the returned row; update runs updateMany with { $set: data }; delete runs deleteMany.
• Tests: src/__tests__/mongo-adapter.test.ts (19 tests) — collection listing, filtered/unfiltered queries, limits, three operator-injection scenarios (a $-prefixed key, a dotted key, an operator-object value), insert/update/delete.

---

Quick Start

1. Connect with one click via Smithery

You can add this to Claude Desktop with one click via Smithery.

2. Connect to Claude Desktop via global install

npm install -g @guardbee/mcp-db-gateway

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS):

{
  "mcpServers": {
    "guardbee-db-gateway": {
      "command": "guardbee-gateway",
      "env": {
        "DATABASE_URL": "postgresql://user:pass@localhost:5432/mydb"
      }
    }
  }
}

Windows: %APPDATA%\Claude\claude_desktop_config.json Linux: ~/.config/Claude/claude_desktop_config.json

Restart Claude Desktop. The demo database loads automatically, with PII masking active.

3. Use it in your project (Prisma)

npm install @guardbee/mcp-db-gateway

import { PrismaClient } from "@prisma/client";
import { createServer, createPrismaAdapter } from "@guardbee/mcp-db-gateway";

const prisma = new PrismaClient();

const server = createServer(
  {
    audit: { enabled: true, sink: "file", filePath: "./audit.jsonl" },
  },
  createPrismaAdapter(prisma)
);

If you don't use Prisma, you can also pass a raw pg or mysql2 connection directly:

// Postgres
import { Pool } from "pg";
import { createServer, createPgAdapter } from "@guardbee/mcp-db-gateway";

const pool = new Pool({ connectionString: process.env.DATABASE_URL });
const server = createServer({}, createPgAdapter(pool /*, { schema: "public" } */));

// MySQL
import mysql from "mysql2/promise";
import { createServer, createMysqlAdapter } from "@guardbee/mcp-db-gateway";

const pool = mysql.createPool(process.env.DATABASE_URL!);
const server = createServer({}, createMysqlAdapter(pool /*, { database: "shop" } */));

// SQLite
import Database from "better-sqlite3";
import { createServer, createSqliteAdapter } from "@guardbee/mcp-db-gateway";

const db = new Database("./app.db");
const server = createServer({}, createSqliteAdapter(db));

// MongoDB
import { MongoClient } from "mongodb";
import { createServer, createMongoAdapter } from "@guardbee/mcp-db-gateway";

const client = new MongoClient(process.env.DATABASE_URL!);
await client.connect();
const server = createServer({}, createMongoAdapter(client.db("mydb")));

Security note: unlike the Prisma adapter, the pg/mysql2/better-sqlite3 adapters generate raw SQL. Because table and column names can't be parameterized, they are validated against the live schema on every query (information_schema, or PRAGMA table_info for SQLite) — a table/column name that isn't in the schema (e.g. an injection attempt) is rejected before it ever reaches SQL. The MongoDB adapter guards against a different risk ("operator injection" instead of SQL) — see Recent Changes.

---

MCP Tools

The gateway always exposes these 5 read tools to Claude:

Tool	Description
query_table	Query rows from a table (PII is masked automatically)
list_tables	List accessible tables (role restrictions applied)
describe_table	Show a table's schema and masking policy
query_audit_log	Query the gateway's own audit history (filterable by table/tool/operation/deniedOnly/since) — in-memory, capped by audit.bufferSize, resets on process restart
gateway_status	Show the active config, roles, and rate-limit status

When writesEnabled: true (see Write Support), 3 more write tools are added:

Tool	Description
insert_row	Inserts a new row
update_row	Updates rows matching a filter (an empty filter is rejected)
delete_row	Deletes rows matching a filter (an empty filter is rejected)

---

Configuration

createServer({
  // PII field rules (the first match applies)
  fieldRules: [
    { field: "tcKimlik",     strategy: "redact" }, // [REDACTED]
    { field: "iban",         strategy: "mask"   }, // TR32***890
    { field: "email",        strategy: "mask"   }, // ah***@example.com
    { field: "passwordHash", strategy: "redact" },
    { field: "*Token*",      strategy: "redact" }, // glob pattern
  ],

  // Table access rules
  tableRules: [
    { table: "audit_logs", access: "deny"  },
    { table: "users",      access: "allow", maxRows: 25 },
    // write: if unspecified, that table has no write permission at all (off by default)
    { table: "orders",     access: "allow", write: { insert: true, update: true, delete: false } },
  ],

  // Turn on the write tools (insert_row/update_row/delete_row) — false by default.
  // While false, these tools are never visible to Claude.
  writesEnabled: true,

  // How many rows update_row/delete_row may affect via one filter.
  // If exceeded, the operation is rejected before touching the database ("narrow your filter").
  maxAffectedRowsPerWrite: 10,

  // Default max rows
  defaultMaxRows: 50,

  // Rate limiting
  rateLimit: {
    enabled: true,
    windowMs: 60_000,          // 1 minute
    maxRequests: 100,           // global limit
    maxRequestsPerTable: 20,    // per table
  },

  // Audit log
  audit: {
    enabled: true,
    sink: "file",              // "console" | "file" | "http"
    filePath: "./audit.jsonl",
    // webhookUrl: "https://..."  (for sink: "http")
    bufferSize: 200,           // size of the in-memory history the `query_audit_log` tool reads
  },

  // Roles
  roles: [
    {
      name: "ai-agent",
      allowTables: ["products", "orders"],  // only these tables
      maxRows: 10,
      // If a role doesn't define write (undefined), write is COMPLETELY off for that role,
      // even if the table allows it. To permit writes, state it explicitly on the role too:
      write: { insert: true, update: true, delete: false },
    },
    {
      name: "analyst",
      denyTables: ["audit_logs"],           // this table is blocked
      fieldRules: [
        { field: "email", strategy: "allow" }, // email unmasked
      ],
      // write not defined → analyst can write nothing
    },
  ],

  // Active role (can also be set via the GATEWAY_ROLE env var)
  activeRole: "ai-agent",
});

---

Masking Strategies

Strategy	Description	Example
redact	The field is removed entirely	[REDACTED]
mask	The middle of the value is starred out	ah***@example.com / 530***67
hash	SHA-256 (first 16 characters)	a665a45920422f9d
allow	Passed through unchanged	[email protected]

Glob pattern support: *Password*, *Token*, *Secret*

PII inside text columns (piiScan)

Field rules go by column name, so a free-text column (notes, description) can still carry an e-mail, a TC kimlik or an API key. piiScan (off by default) masks those by value in every text field no field rule covers, nested objects and arrays included; an allow rule turns it off for that field. preset / enable / disable pick the detectors, with the same presets as the security proxy: ALL (default), KVKK, IDENTITY, IDENTIFIERS, SECRETS.

createServer({ piiScan: { enabled: true, preset: "KVKK", disable: ["address"] } }, adapter);

From the CLI: GATEWAY_PII_SCAN=true (every default detector) or GATEWAY_PII_SCAN=KVKK (a preset). An unknown preset or detector name fails at startup.

piiScan.blockPatterns and piiScan.allowPatterns add your own patterns, as in the security proxy: block masks your ids as <CATEGORY_n>, allow leaves a detected value whose whole text matches. A block pattern that runs over its 100 ms budget fails the query rather than return rows it may not have masked.

createServer({ piiScan: { enabled: true, blockPatterns: [{ pattern: "CL-\\d{6}", category: "CLIENT_NO" }], allowPatterns: ["destek@acme\\.com\\.tr"] } }, adapter);

---

Role-Based Access (RBAC)

The role is set when the server starts, via the GATEWAY_ROLE env var or config.activeRole. Each Claude Desktop profile or deployment can run with a different role.

GATEWAY_ROLE=analyst node dist/cli.js

Rule precedence (highest to lowest):

1. Global tableRules deny
2. Role denyTables
3. Role allowTables (a whitelist — if set, the table must be in this list)
4. Role fieldRules → global fieldRules

---

Write Support (write/insert/update/delete)

The gateway is fully read-only by default. Letting the LLM modify data requires deliberately unlocking a few gates:

1. writesEnabled: true — the global kill-switch. While false (default), insert_row/update_row/delete_row are never visible to Claude.
2. Table permission — tableRules[].write.{insert,update,delete} — per table, off by default for all.
3. Role permission (when a role is active) — roles[].write.{insert,update,delete}. If a role never defines write (undefined), write is completely off for that role — even if the table permits it. To permit a write, both the table and the role must explicitly say true (AND logic — deliberately stricter than the "role overrides" logic used for masking rules).

Beyond these three gates, there are two more protections that cannot be disabled:

• Protected-field guarding — the LLM can never write a value into a field marked redact/mask/hash in fieldRules (e.g. tcKimlik, passwordHash); if insert_row/update_row sees such a field in data, the whole request is rejected.
• maxAffectedRowsPerWrite — before update_row/delete_row runs, the filter is first tried as a read; if the matched row count exceeds this limit (default 10), the operation is rejected before touching anything. update_row/delete_row also always reject an empty filter — "update/delete the whole table" is never possible through this gateway.

Every write attempt (accepted or denied) is written to the audit log; only which fields were written is logged, never data itself (so the audit log itself can't become a PII leak point).

createServer({
  writesEnabled: true,
  maxAffectedRowsPerWrite: 10,
  tableRules: [
    { table: "orders", access: "allow", write: { insert: true, update: true, delete: false } },
  ],
  roles: [
    { name: "ai-agent", allowTables: ["orders"], write: { insert: true, update: true, delete: false } },
  ],
  activeRole: "ai-agent",
});

---

Prisma Adapter

Pass a PrismaClient directly — table name → model mapping is automatic:

Query table	Prisma model
"users"	prisma.user
"audit_logs"	prisma.auditLog
"orders"	prisma.order
"orderItems"	prisma.orderItem

---

Development

npm run dev          # dev mode via tsx
npm run build        # TypeScript compile
npm test             # 195 unit tests
npm run test:watch   # watch mode
npm run type-check   # type-check only

---

License

MIT — GuardBee

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