API Security Best Practices: The Checklist I Run on Every Project

import jwt from "jsonwebtoken";
import { timingSafeEqual } from "crypto";
 
interface TokenPayload {
  sub: string;
  role: "user" | "admin";
  iss: string;
  aud: string;
  exp: number;
  iat: number;
  jti: string;
}
 
function verifyToken(token: string): TokenPayload {
  try {
    const payload = jwt.verify(token, process.env.JWT_SECRET!, {
      algorithms: ["HS256"], // Never allow "none"
      issuer: "api.yourapp.com",
      audience: "yourapp.com",
      clockTolerance: 30, // 30 seconds leeway for clock skew
    }) as TokenPayload;
 
    return payload;
  } catch (error) {
    if (error instanceof jwt.TokenExpiredError) {
      throw new ApiError(401, "Token expired");
    }
    if (error instanceof jwt.JsonWebTokenError) {
      throw new ApiError(401, "Invalid token");
    }
    throw new ApiError(401, "Authentication failed");
  }
}

import { randomBytes } from "crypto";
import { redis } from "./redis";
 
interface RefreshTokenData {
  userId: string;
  family: string; // Token family for rotation detection
  createdAt: number;
}
 
async function rotateRefreshToken(oldRefreshToken: string): Promise<{ accessToken: string; refreshToken: string }> {
  const tokenData = await redis.get(`refresh:${oldRefreshToken}`);
 
  if (!tokenData) {
    // Token not found — either expired or already used.
    // If already used, this is a potential replay attack.
    // Invalidate the entire token family.
    const parsed = decodeRefreshToken(oldRefreshToken);
    if (parsed?.family) {
      await invalidateTokenFamily(parsed.family);
    }
    throw new ApiError(401, "Invalid refresh token");
  }
 
  const data: RefreshTokenData = JSON.parse(tokenData);
 
  // Delete the old token immediately — single use only
  await redis.del(`refresh:${oldRefreshToken}`);
 
  // Generate new tokens
  const newRefreshToken = randomBytes(64).toString("hex");
  const newAccessToken = generateAccessToken(data.userId);
 
  // Store the new refresh token with the same family
  await redis.setex(
    `refresh:${newRefreshToken}`,
    60 * 60 * 24 * 30, // 30 days
    JSON.stringify({
      userId: data.userId,
      family: data.family,
      createdAt: Date.now(),
    }),
  );
 
  return { accessToken: newAccessToken, refreshToken: newRefreshToken };
}
 
async function invalidateTokenFamily(family: string): Promise<void> {
  // Scan for all tokens in this family and delete them.
  // This is the nuclear option — if someone replays a refresh token,
  // we kill every token in the family, forcing re-authentication.
  const keys = await redis.keys(`refresh:*`);
  for (const key of keys) {
    const data = await redis.get(key);
    if (data) {
      const parsed = JSON.parse(data) as RefreshTokenData;
      if (parsed.family === family) {
        await redis.del(key);
      }
    }
  }
}

// Setting a secure refresh token cookie
function setRefreshTokenCookie(res: Response, token: string): void {
  res.cookie("refresh_token", token, {
    httpOnly: true, // Not accessible via JavaScript
    secure: true, // HTTPS only
    sameSite: "strict", // No cross-site requests
    maxAge: 30 * 24 * 60 * 60 * 1000, // 30 days
    path: "/api/auth", // Only sent to auth endpoints
  });
}

import { z } from "zod";
 
const CreateUserSchema = z.object({
  email: z
    .string()
    .email("Invalid email format")
    .max(254, "Email too long")
    .transform((e) => e.toLowerCase().trim()),
 
  password: z
    .string()
    .min(12, "Password must be at least 12 characters")
    .max(128, "Password too long") // Prevent bcrypt DoS
    .regex(/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)/, "Password must contain uppercase, lowercase, and a number"),
 
  name: z
    .string()
    .min(1, "Name is required")
    .max(100, "Name too long")
    .regex(/^[\p{L}\p{M}\s'-]+$/u, "Name contains invalid characters"),
 
  role: z.enum(["user", "editor"]).default("user"),
  // Note: "admin" is intentionally not an option here.
  // Admin role assignment goes through a separate, privileged endpoint.
});
 
type CreateUserInput = z.infer<typeof CreateUserSchema>;
 
// Usage in an Express handler
app.post("/api/users", async (req, res) => {
  const result = CreateUserSchema.safeParse(req.body);
 
  if (!result.success) {
    return res.status(400).json({
      error: "Validation failed",
      details: result.error.issues.map((issue) => ({
        field: issue.path.join("."),
        message: issue.message,
      })),
    });
  }
 
  // result.data is fully typed as CreateUserInput
  const user = await createUser(result.data);
  return res.status(201).json({ id: user.id, email: user.email });
});

// VULNERABLE — string concatenation
const query = `SELECT * FROM users WHERE email = '${email}'`;
 
// SAFE — parameterized query
const query = `SELECT * FROM users WHERE email = $1`;
const result = await pool.query(query, [email]);

// VULNERABLE — template literal in $queryRaw
const users = await prisma.$queryRaw`
  SELECT * FROM users WHERE name LIKE '%${searchTerm}%'
`;
 
// SAFE — using Prisma.sql for parameterization
import { Prisma } from "@prisma/client";
 
const users = await prisma.$queryRaw(Prisma.sql`SELECT * FROM users WHERE name LIKE ${`%${searchTerm}%`}`);

// VULNERABLE — if req.body.username is { "$gt": "" }
// this returns the first user in the collection
const user = await db.collection("users").findOne({
  username: req.body.username,
});
 
// SAFE — explicitly coerce to string
const user = await db.collection("users").findOne({
  username: String(req.body.username),
});
 
// BETTER — validate with Zod first
const LoginSchema = z.object({
  username: z.string().min(1).max(50),
  password: z.string().min(1).max(128),
});

import path from "path";
import { access, constants } from "fs/promises";
 
const ALLOWED_DIR = "/app/uploads";
 
async function resolveUserFilePath(userInput: string): Promise<string> {
  // Normalize and resolve to an absolute path
  const resolved = path.resolve(ALLOWED_DIR, userInput);
 
  // Critical: verify the resolved path is still within the allowed directory
  if (!resolved.startsWith(ALLOWED_DIR + path.sep)) {
    throw new ApiError(403, "Access denied");
  }
 
  // Verify the file actually exists
  await access(resolved, constants.R_OK);
 
  return resolved;
}
 
// Without this check:
// GET /api/files?name=../../../etc/passwd
// resolves to /etc/passwd

import { Redis } from "ioredis";
 
interface RateLimitResult {
  allowed: boolean;
  remaining: number;
  resetAt: number;
}
 
async function slidingWindowRateLimit(
  redis: Redis,
  key: string,
  limit: number,
  windowMs: number,
): Promise<RateLimitResult> {
  const now = Date.now();
  const windowStart = now - windowMs;
 
  const multi = redis.multi();
 
  // Remove entries outside the window
  multi.zremrangebyscore(key, 0, windowStart);
 
  // Count entries in the window
  multi.zcard(key);
 
  // Add the current request (we'll remove it if over limit)
  multi.zadd(key, now.toString(), `${now}:${Math.random()}`);
 
  // Set expiry on the key
  multi.pexpire(key, windowMs);
 
  const results = await multi.exec();
 
  if (!results) {
    throw new Error("Redis transaction failed");
  }
 
  const count = results[1][1] as number;
 
  if (count >= limit) {
    // Over limit — remove the entry we just added
    await redis.zremrangebyscore(key, now, now);
 
    return {
      allowed: false,
      remaining: 0,
      resetAt: windowStart + windowMs,
    };
  }
 
  return {
    allowed: true,
    remaining: limit - count - 1,
    resetAt: now + windowMs,
  };
}

interface RateLimitConfig {
  window: number;
  max: number;
}
 
const RATE_LIMITS: Record<string, RateLimitConfig> = {
  // Auth endpoints — tight limits, brute force target
  "POST:/api/auth/login": { window: 15 * 60 * 1000, max: 5 },
  "POST:/api/auth/register": { window: 60 * 60 * 1000, max: 3 },
  "POST:/api/auth/reset-password": { window: 60 * 60 * 1000, max: 3 },
 
  // Data reads — more generous
  "GET:/api/users": { window: 60 * 1000, max: 100 },
  "GET:/api/products": { window: 60 * 1000, max: 200 },
 
  // Data writes — moderate
  "POST:/api/posts": { window: 60 * 1000, max: 10 },
  "PUT:/api/posts": { window: 60 * 1000, max: 30 },
 
  // Global fallback
  "*": { window: 60 * 1000, max: 60 },
};
 
function getRateLimitKey(req: Request, config: RateLimitConfig): string {
  const identifier = req.user?.id ?? getClientIp(req);
  const endpoint = `${req.method}:${req.path}`;
  return `ratelimit:${identifier}:${endpoint}`;
}

function setRateLimitHeaders(res: Response, result: RateLimitResult, limit: number): void {
  res.set({
    "X-RateLimit-Limit": limit.toString(),
    "X-RateLimit-Remaining": result.remaining.toString(),
    "X-RateLimit-Reset": Math.ceil(result.resetAt / 1000).toString(),
    "Retry-After": result.allowed ? undefined : Math.ceil((result.resetAt - Date.now()) / 1000).toString(),
  });
 
  if (!result.allowed) {
    res.status(429).json({
      error: "Too many requests",
      retryAfter: Math.ceil((result.resetAt - Date.now()) / 1000),
    });
  }
}

// DANGEROUS — allows any website to read your API responses
app.use(cors({ origin: "*" }));
 
// ALSO DANGEROUS — this is a common "dynamic" approach that's just * with extra steps
app.use(
  cors({
    origin: (origin, callback) => {
      callback(null, true); // Allows everything
    },
  }),
);

import cors from "cors";
 
const ALLOWED_ORIGINS = new Set(["https://yourapp.com", "https://www.yourapp.com", "https://admin.yourapp.com"]);
 
if (process.env.NODE_ENV === "development") {
  ALLOWED_ORIGINS.add("http://localhost:3000");
  ALLOWED_ORIGINS.add("http://localhost:5173");
}
 
app.use(
  cors({
    origin: (origin, callback) => {
      // Allow requests with no origin (mobile apps, curl, server-to-server)
      if (!origin) {
        return callback(null, true);
      }
 
      if (ALLOWED_ORIGINS.has(origin)) {
        return callback(null, origin);
      }
 
      callback(new Error(`Origin ${origin} not allowed by CORS`));
    },
    credentials: true, // Allow cookies
    methods: ["GET", "POST", "PUT", "DELETE", "PATCH"],
    allowedHeaders: ["Content-Type", "Authorization"],
    exposedHeaders: ["X-RateLimit-Limit", "X-RateLimit-Remaining"],
    maxAge: 86400, // Cache preflight for 24 hours
  }),
);

// Manual preflight handling (most frameworks do this for you)
app.options("*", (req, res) => {
  res.set({
    "Access-Control-Allow-Origin": getAllowedOrigin(req.headers.origin),
    "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, PATCH",
    "Access-Control-Allow-Headers": "Content-Type, Authorization",
    "Access-Control-Max-Age": "86400",
  });
  res.status(204).end();
});

import helmet from "helmet";
 
// One line. This is the fastest security win in any Express app.
app.use(
  helmet({
    contentSecurityPolicy: {
      directives: {
        defaultSrc: ["'self'"],
        scriptSrc: ["'self'"],
        styleSrc: ["'self'", "'unsafe-inline'"], // Needed for many CSS-in-JS solutions
        imgSrc: ["'self'", "data:", "https:"],
        connectSrc: ["'self'", "https://api.yourapp.com"],
        fontSrc: ["'self'"],
        objectSrc: ["'none'"],
        mediaSrc: ["'self'"],
        frameSrc: ["'none'"],
        upgradeInsecureRequests: [],
      },
    },
    hsts: {
      maxAge: 31536000, // 1 year
      includeSubDomains: true,
      preload: true,
    },
    referrerPolicy: { policy: "strict-origin-when-cross-origin" },
  }),
);

import { describe, it, expect } from "vitest";
 
describe("Security headers", () => {
  it("should include all required security headers", async () => {
    const response = await fetch("https://api.yourapp.com/health");
 
    expect(response.headers.get("strict-transport-security")).toBeTruthy();
    expect(response.headers.get("x-content-type-options")).toBe("nosniff");
    expect(response.headers.get("x-frame-options")).toBe("SAMEORIGIN");
    expect(response.headers.get("content-security-policy")).toBeTruthy();
    expect(response.headers.get("referrer-policy")).toBeTruthy();
    expect(response.headers.get("x-powered-by")).toBeNull(); // Helmet removes this
  });
});

# .env.example — commit this
DATABASE_URL=postgresql://user:password@localhost:5432/dbname
JWT_SECRET=your-secret-here
REDIS_URL=redis://localhost:6379
SMTP_API_KEY=your-smtp-key
 
# .env — NEVER commit this
# Listed in .gitignore

import { z } from "zod";
 
const envSchema = z.object({
  DATABASE_URL: z.string().url(),
  JWT_SECRET: z.string().min(32, "JWT secret must be at least 32 characters"),
  REDIS_URL: z.string().url(),
  NODE_ENV: z.enum(["development", "production", "test"]).default("development"),
  PORT: z.coerce.number().default(3000),
  CORS_ORIGINS: z.string().transform((s) => s.split(",")),
});
 
export type Env = z.infer<typeof envSchema>;
 
function validateEnv(): Env {
  const result = envSchema.safeParse(process.env);
 
  if (!result.success) {
    console.error("Invalid environment variables:");
    console.error(result.error.format());
    process.exit(1); // Don't start with bad config
  }
 
  return result.data;
}
 
export const env = validateEnv();

interface SigningKey {
  id: string;
  secret: string;
  createdAt: Date;
  active: boolean; // Only the active key signs new tokens
}
 
async function verifyWithRotation(token: string): Promise<TokenPayload> {
  const keys = await getSigningKeys(); // Returns all valid keys
 
  for (const key of keys) {
    try {
      return jwt.verify(token, key.secret, {
        algorithms: ["HS256"],
      }) as TokenPayload;
    } catch {
      continue; // Try the next key
    }
  }
 
  throw new ApiError(401, "Invalid token");
}
 
function signToken(payload: Omit<TokenPayload, "iat" | "exp">): string {
  const activeKey = getActiveSigningKey();
  return jwt.sign(payload, activeKey.secret, {
    algorithm: "HS256",
    expiresIn: "15m",
    keyid: activeKey.id, // Include key ID in the header
  });
}

// VULNERABLE — any authenticated user can access any user's data
app.get("/api/users/:id", authenticate, async (req, res) => {
  const user = await db.users.findById(req.params.id);
  return res.json(user);
});
 
// FIXED — verify the user is accessing their own data (or is an admin)
app.get("/api/users/:id", authenticate, async (req, res) => {
  if (req.user.id !== req.params.id && req.user.role !== "admin") {
    return res.status(403).json({ error: "Access denied" });
  }
  const user = await db.users.findById(req.params.id);
  return res.json(user);
});

const MAX_LOGIN_ATTEMPTS = 5;
const LOCKOUT_DURATION = 15 * 60 * 1000; // 15 minutes
 
async function handleLogin(email: string, password: string): Promise<AuthResult> {
  const lockoutKey = `lockout:${email}`;
  const attempts = await redis.get(lockoutKey);
 
  if (attempts && parseInt(attempts) >= MAX_LOGIN_ATTEMPTS) {
    const ttl = await redis.pttl(lockoutKey);
    throw new ApiError(429, `Account locked. Try again in ${Math.ceil(ttl / 60000)} minutes.`);
  }
 
  const user = await db.users.findByEmail(email);
 
  if (!user || !(await bcrypt.compare(password, user.passwordHash))) {
    // Increment failed attempts
    await redis.multi().incr(lockoutKey).pexpire(lockoutKey, LOCKOUT_DURATION).exec();
 
    // Same error message for both cases — don't reveal whether the email exists
    throw new ApiError(401, "Invalid email or password");
  }
 
  // Reset failed attempts on successful login
  await redis.del(lockoutKey);
 
  return generateTokens(user);
}

// VULNERABLE — returns the entire user object, including internal fields
app.get("/api/users/:id", authenticate, authorize, async (req, res) => {
  const user = await db.users.findById(req.params.id);
  return res.json(user);
  // Response includes: passwordHash, internalNotes, billingId, ...
});
 
// FIXED — explicit allowlist of returned fields
app.get("/api/users/:id", authenticate, authorize, async (req, res) => {
  const user = await db.users.findById(req.params.id);
  return res.json({
    id: user.id,
    name: user.name,
    email: user.email,
    avatar: user.avatar,
    createdAt: user.createdAt,
  });
});

// VULNERABLE — mass assignment
app.put("/api/users/:id", authenticate, async (req, res) => {
  await db.users.update(req.params.id, req.body);
  // Attacker sends: { "role": "admin", "verified": true }
});
 
// FIXED — pick allowed fields
const UpdateUserSchema = z.object({
  name: z.string().min(1).max(100).optional(),
  avatar: z.string().url().optional(),
});
 
app.put("/api/users/:id", authenticate, async (req, res) => {
  const data = UpdateUserSchema.parse(req.body);
  await db.users.update(req.params.id, data);
});

// Limit request body size
app.use(express.json({ limit: "1mb" }));
 
// Limit query complexity
const MAX_PAGE_SIZE = 100;
const DEFAULT_PAGE_SIZE = 20;
 
const PaginationSchema = z.object({
  page: z.coerce.number().int().positive().default(1),
  limit: z.coerce.number().int().positive().max(MAX_PAGE_SIZE).default(DEFAULT_PAGE_SIZE),
});
 
// Limit file upload size
const upload = multer({
  limits: {
    fileSize: 5 * 1024 * 1024, // 5MB
    files: 1,
  },
  fileFilter: (req, file, cb) => {
    const allowed = ["image/jpeg", "image/png", "image/webp"];
    if (allowed.includes(file.mimetype)) {
      cb(null, true);
    } else {
      cb(new Error("Invalid file type"));
    }
  },
});
 
// Timeout long-running requests
app.use((req, res, next) => {
  res.setTimeout(30000, () => {
    res.status(408).json({ error: "Request timeout" });
  });
  next();
});

// Middleware that checks role-based access
function requireRole(...allowedRoles: string[]) {
  return (req: Request, res: Response, next: NextFunction) => {
    if (!req.user) {
      return res.status(401).json({ error: "Not authenticated" });
    }
 
    if (!allowedRoles.includes(req.user.role)) {
      // Log the attempt — this might be an attack
      logger.warn("Unauthorized access attempt", {
        userId: req.user.id,
        role: req.user.role,
        requiredRoles: allowedRoles,
        endpoint: `${req.method} ${req.path}`,
        ip: req.ip,
      });
 
      return res.status(403).json({ error: "Insufficient permissions" });
    }
 
    next();
  };
}
 
// Apply to routes
app.delete("/api/users/:id", authenticate, requireRole("admin"), deleteUser);
app.get("/api/admin/stats", authenticate, requireRole("admin"), getStats);
app.post("/api/posts", authenticate, requireRole("admin", "editor"), createPost);

import { URL } from "url";
import dns from "dns/promises";
import { isPrivateIP } from "./network-utils";
 
async function safeFetch(userProvidedUrl: string): Promise<Response> {
  let parsed: URL;
 
  try {
    parsed = new URL(userProvidedUrl);
  } catch {
    throw new ApiError(400, "Invalid URL");
  }
 
  // Only allow HTTP(S)
  if (!["http:", "https:"].includes(parsed.protocol)) {
    throw new ApiError(400, "Only HTTP(S) URLs are allowed");
  }
 
  // Resolve the hostname and check if it's a private IP
  const addresses = await dns.resolve4(parsed.hostname);
 
  for (const addr of addresses) {
    if (isPrivateIP(addr)) {
      throw new ApiError(400, "Internal addresses are not allowed");
    }
  }
 
  // Now fetch with a timeout and size limit
  const controller = new AbortController();
  const timeout = setTimeout(() => controller.abort(), 5000);
 
  try {
    const response = await fetch(userProvidedUrl, {
      signal: controller.signal,
      redirect: "error", // Don't follow redirects (they could redirect to internal IPs)
    });
 
    return response;
  } finally {
    clearTimeout(timeout);
  }
}

// Don't leak stack traces in production
app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
  logger.error("Unhandled error", {
    error: err.message,
    stack: err.stack,
    path: req.path,
    method: req.method,
  });
 
  if (process.env.NODE_ENV === "production") {
    // Generic error message — don't reveal internals
    res.status(500).json({
      error: "Internal server error",
      requestId: req.id, // Include a request ID for debugging
    });
  } else {
    // In development, show the full error
    res.status(500).json({
      error: err.message,
      stack: err.stack,
    });
  }
});
 
// Disable unnecessary HTTP methods
app.use((req, res, next) => {
  const allowed = ["GET", "POST", "PUT", "DELETE", "PATCH", "OPTIONS"];
  if (!allowed.includes(req.method)) {
    return res.status(405).json({ error: "Method not allowed" });
  }
  next();
});

import crypto from "crypto";
 
// Verify Stripe webhook signatures
function verifyStripeWebhook(payload: string, signature: string, secret: string): boolean {
  const timestamp = signature
    .split(",")
    .find((s) => s.startsWith("t="))
    ?.slice(2);
  const expectedSig = signature
    .split(",")
    .find((s) => s.startsWith("v1="))
    ?.slice(3);
 
  if (!timestamp || !expectedSig) return false;
 
  // Reject old timestamps (prevent replay attacks)
  const age = Math.abs(Date.now() / 1000 - parseInt(timestamp));
  if (age > 300) return false; // 5 minute tolerance
 
  const signedPayload = `${timestamp}.${payload}`;
  const computedSig = crypto.createHmac("sha256", secret).update(signedPayload).digest("hex");
 
  return crypto.timingSafeEqual(Buffer.from(computedSig), Buffer.from(expectedSig));
}

interface AuditLogEntry {
  timestamp: string;
  action: string; // "user.login", "post.delete", "admin.role_change"
  actor: {
    id: string;
    ip: string;
    userAgent: string;
  };
  target: {
    type: string; // "user", "post", "setting"
    id: string;
  };
  result: "success" | "failure";
  metadata: Record<string, unknown>; // Additional context
  requestId: string; // For correlating with application logs
}
 
async function auditLog(entry: AuditLogEntry): Promise<void> {
  // Write to a separate, append-only data store
  // This should NOT be the same database your application uses
  await auditDb.collection("audit_logs").insertOne({
    ...entry,
    timestamp: new Date().toISOString(),
  });
 
  // For critical actions, also write to an immutable external log
  if (isCriticalAction(entry.action)) {
    await externalLogger.send(entry);
  }
}

function sanitizeForLogging(data: Record<string, unknown>): Record<string, unknown> {
  const sensitiveKeys = new Set([
    "password",
    "passwordHash",
    "token",
    "secret",
    "apiKey",
    "creditCard",
    "ssn",
    "authorization",
  ]);
 
  const sanitized: Record<string, unknown> = {};
 
  for (const [key, value] of Object.entries(data)) {
    if (sensitiveKeys.has(key.toLowerCase())) {
      sanitized[key] = "[REDACTED]";
    } else if (typeof value === "object" && value !== null) {
      sanitized[key] = sanitizeForLogging(value as Record<string, unknown>);
    } else {
      sanitized[key] = value;
    }
  }
 
  return sanitized;
}

import crypto from "crypto";
 
let previousHash = "GENESIS"; // The initial hash in the chain
 
function createTamperEvidentEntry(entry: AuditLogEntry): AuditLogEntry & { hash: string } {
  const content = JSON.stringify(entry) + previousHash;
  const hash = crypto.createHash("sha256").update(content).digest("hex");
 
  previousHash = hash;
 
  return { ...entry, hash };
}
 
// To verify the chain integrity:
function verifyLogChain(entries: Array<AuditLogEntry & { hash: string }>): boolean {
  let expectedPreviousHash = "GENESIS";
 
  for (const entry of entries) {
    const { hash, ...rest } = entry;
    const content = JSON.stringify(rest) + expectedPreviousHash;
    const computedHash = crypto.createHash("sha256").update(content).digest("hex");
 
    if (computedHash !== hash) {
      return false; // Chain is broken — logs have been tampered with
    }
 
    expectedPreviousHash = hash;
  }
 
  return true;
}

# Run this in CI, fail the build on high/critical vulnerabilities
npm audit --audit-level=high
 
# Fix what can be auto-fixed
npm audit fix
 
# See what you're actually pulling in
npm ls --all

# .github/dependabot.yml
version: 2
updates:
  - package-ecosystem: "npm"
    directory: "/"
    schedule:
      interval: "weekly"
    open-pull-requests-limit: 10
    reviewers:
      - "your-team"
    labels:
      - "dependencies"
    # Group minor and patch updates to reduce PR noise
    groups:
      production-dependencies:
        patterns:
          - "*"
        update-types:
          - "minor"
          - "patch"

# In CI, use ci instead of install — it respects the lockfile strictly
npm ci

// You don't need a package for this:
const isEven = (n: number): boolean => n % 2 === 0;
 
// Or this:
const leftPad = (str: string, len: number, char = " "): string => str.padStart(len, char);
 
// Or this:
const isNil = (value: unknown): value is null | undefined => value === null || value === undefined;