Comparisons
Best Free Authentication Services for Your App: 7 Options With Real User Limits
Auth0, Clerk, Firebase, Kinde, PropelAuth, Stytch and WorkOS compared on free monthly user limits, custom domains and the SSO fees that show up later. Checked against current pricing pages in October 2026.
Building login yourself sounds like an afternoon. It is a month. Password resets, email verification, social sign in, rate limits, session security and a pile of edge cases you will meet one angry user at a time. Hosted authentication exists so you never write that code, and in 2026 the free plans are big enough to carry you well past launch.
The user counts below look similar, but the fine print is not. Here are seven free authentication services, with the number that matters and the limit that stings.
Compare three things before the user count
Monthly active users is the headline number and it is the least interesting one. Check these first.
- Custom domain: can your login page live on your own address, and does that cost extra?
- What happens past the cap: a clean upgrade path or a price cliff?
- SSO and organizations: free plans rarely include enterprise sign in, and per connection fees add up fast.
The big free allowances
WorkOS AuthKit
The first 1 million monthly active users are free, which is the largest allowance here by a mile. You do not need a card until you are ready for production. The trade is that branding costs money: a custom domain is $99 a month and SSO is $125 per connection. Great for a consumer app, expensive the moment you chase enterprise customers. See WorkOS AuthKit.
Clerk
The Hobby plan covers the first 50,000 monthly retained users per app with no card, includes a custom domain, and gives you 3 dashboard seats. Past 50,000 you move to Pro and pay overage from $0.02 per user a month. Past 100 monthly retained organizations you need the B2B add on. Prebuilt components make it the quickest to set up. Read the Clerk listing.
Firebase Authentication
The no cost Spark plan covers 50,000 monthly active users with no payment method. The sharp edges are the daily email caps: 150 password reset emails and just 5 email link sign in emails a day. Phone sign in is not available on Spark at all, so SMS login needs the pay as you go Blaze plan, billed per message. See Firebase Authentication.
Auth0
Up to 25,000 monthly active users, no card to sign up, unlimited social connections and passwordless login. A custom domain is included but you must verify a credit card to switch it on. Past 25,000 users you move to a paid plan, and cost at scale is the loudest complaint in reviews. Go in knowing that, and check the Auth0 page before you commit.
Smaller caps, friendlier for B2B
Stytch
10,000 monthly active users are always free, with unlimited organizations and 5 SSO or SCIM connections included. The page says features are not gated. Extra SSO connections cost $125 each, and removing the Stytch brand from emails is a $99 add on. See Stytch.
PropelAuth
The free plan includes 10,000 monthly active users, unlimited organizations, a custom domain, 2FA and role based access. SMS based 2FA, SAML and enterprise SSO are not included. SSO starts on the Growth plan. If your product is B2B from day one, the unlimited organizations are the draw. See PropelAuth.
Kinde
10,500 monthly active users free, with email, SMS and social login plus multi factor authentication and a custom domain. The caps hide in the details: 2 custom roles, 10 permissions, 1 webhook and only 5 monthly active organizations. It also charges a 0.7% platform fee if you collect payments through Kinde. Read the Kinde entry.
What about Supabase Auth?
If you already use Supabase for your database, its built in auth covers 50,000 monthly active users on the free plan and sits next to your data and row level security. For a lot of first apps, that is the shortest path and one less vendor.
How to choose
- Consumer app with a big free audience: WorkOS AuthKit or Firebase.
- Fastest setup with polished screens: Clerk.
- B2B tool with teams and organizations: PropelAuth or Stytch.
- Already on Postgres with Supabase: use its auth and skip the extra account.
One last habit that saves pain: store your own user ID in your database and map it to the provider's ID. That way, switching providers later means a data migration instead of a rewrite. Also confirm the rules on the pricing page before you launch, because free plans in this category change often.