Use a hosted sign-in service such as Clerk instead of writing your own, send email with Resend from a domain you own, practise payments in Razorpay's test mode, block bots with Cloudflare Turnstile, and watch your app with PostHog, Sentry and UptimeRobot. Stripe is invite-only for new Indian businesses, so Razorpay is the practical payments route in India.
An app is more than screens and a database. Sign-in, email, payments and error alerts are what real users touch, and they are also where AI-generated code takes the most risks. These free services handle the hard parts so you do not write them from scratch.
The 14 picks
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Free, 50,000 usersClerk
Ready-made sign-in and sign-up screens for React and Next.js. The free plan needs no card and covers 50,000 retained users per app. It does not include multi-factor sign-in or removal of Clerk branding.
Free, MIT licenceBetter Auth
Open-source TypeScript auth library that runs inside your own app, with two-factor and passkey plugins. The team also maintains Auth.js and recommends Better Auth for new projects. You provide the database and hosting.
Free, 10,500 usersKinde
Hosted auth with social sign-in, custom domain and organisation support. Free and no card for up to 10,500 monthly active users. Check its feature table before promising multi-factor sign-in.
Free, 1 million usersWorkOS AuthKit
Login with email, social sign-in, passkeys and multi-factor included. The first million monthly active users are free; enterprise single sign-on is billed per connection.
Free, 3,000 emails a monthResend
Email API for sign-up and receipt emails. Free: 3,000 emails a month and 100 a day. The test sender only reaches your own address, so sending to real users needs a domain you own.
Free, 300 emails a dayBrevo
Newsletters and transactional email with a no-card free plan. After account approval you can send up to 300 emails a day, including through its API and SMTP.
Free test modeRazorpay (test mode)
Indian payment gateway for cards, UPI and netbanking. Test mode works right after sign-up with no real money, and test keys can be created without a website. Going live needs account verification.
Free test modeStripe (test mode)
Global payments with a free test mode and test cards. Stripe's own help says its services are invite-only in India, so new Indian businesses cannot sign up on the website. Good for learning the flow.
Free, 20 widgetsCloudflare Turnstile
A free alternative to CAPTCHA for sign-up and contact forms: up to 20 widgets and unlimited checks. You must still verify the token on your server, or bots can call your API directly.
Free, 25 credits a monthCloudinary
Image and video upload, resizing and delivery. The free plan gives 25 credits a month with no card; one credit is 1,000 transformations or 1 GB of storage or bandwidth.
Free, 1 million eventsPostHog
Product analytics, session replay, feature flags and error tracking. Free, no card: 1 million events and 5,000 recordings a month. Usage stops at the limit rather than billing you.
Free, 5,000 errors a monthSentry
Shows the stack trace behind a user's crash. The free plan has one user, 5,000 errors a month and a 30-day lookback. A noisy bug can use the month's errors quickly.
Free, 50 monitorsUptimeRobot
Checks your site every five minutes and alerts you when it is down. Free with no card: 50 monitors and a status page; the site says the free plan is fine for personal and commercial projects.
Free, 1 siteUmami
Simple, cookie-free web analytics. The hosted free plan covers one website and 100,000 events a month, and you can self-host it for free under the MIT licence.
Compare in a table
Show the full comparison table
| Tool | Best for | Free plan |
|---|---|---|
| Clerk | Fast, polished login | Free, 50,000 users |
| Better Auth | Own your auth, no user fees | Free, MIT licence |
| Kinde | Auth with a custom domain | Free, 10,500 users |
| WorkOS AuthKit | Business-ready sign-in | Free, 1 million users |
| Resend | Emails from your own domain | Free, 3,000 emails a month |
| Brevo | Newsletters and alerts | Free, 300 emails a day |
| Razorpay (test mode) | First UPI and card payments | Free test mode |
| Stripe (test mode) | Learning payments, overseas apps | Free test mode |
| Cloudflare Turnstile | Stopping bots on forms | Free, 20 widgets |
| Cloudinary | Image resizing and delivery | Free, 25 credits a month |
| PostHog | Seeing how people use the app | Free, 1 million events |
| Sentry | Catching production errors | Free, 5,000 errors a month |
| UptimeRobot | Uptime alerts | Free, 50 monitors |
| Umami | Simple privacy-friendly analytics | Free, 1 site |
Get started this week
- Add Clerk or Supabase Auth and test sign-up with two different emails.
- Create Razorpay test keys and run one test payment, verifying the signature on the server.
- Add an UptimeRobot monitor and Sentry to the live link.
How to choose
- Never write your own password handling; use a hosted service or a library such as Better Auth.
- Create orders and check payment signatures on the server, never in the browser, and keep secret keys out of front-end code.
- Add Turnstile to sign-up and contact forms before sharing the link.
- Set up UptimeRobot and Sentry before real users arrive so you hear about problems before they do.
Free plans change. Limits above were checked on 3 Nov 2026; confirm on each tool's pricing page before relying on them.
Frequently asked questions
What is the easiest free login for a vibe-coded app?
Clerk's free plan gives ready-made sign-in screens for 50,000 retained users. If you already use Supabase, its built-in Auth is the simplest, but its default email is limited to two messages an hour, so add custom SMTP for real users.
How do I send email from a free app?
Use Resend or Brevo through their HTTP APIs. Resend's test sender only reaches your own address, so to email real users you need a domain you own and its DNS records.
Can I use Stripe in India?
Stripe's help pages say its services are invite-only in India and Indian businesses cannot sign up on the website. Razorpay's test mode is open at sign-up, so use it to practise.
Is it safe to put payment keys in an AI-built app?
Only the public key belongs in the browser. Secret keys and webhook secrets must stay on a server or serverless function, and the server should verify every payment signature before unlocking anything.
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