Phone sign-in is not on Spark, so plan for per-SMS billing on Blaze. Firebase Authentication is Google's sign-in service for web and mobile apps. On the no-cost Spark plan the pricing page lists 50K monthly active users and 50 monthly active users for SAML and OIDC, with no payment method needed. Phone authentication is not available on Spark and is billed per SMS on the pay-as-you-go Blaze plan, where usage above 50K MAUs follows Google Cloud Identity Platform pricing. The limits page caps Spark at 1,000 address verification emails a day, 150 password reset emails and 5 email-link sign-in emails, and caps Firebase Authentication SMS at 3,000 a day. The reviews I found cover Firebase as a whole rather than Authentication alone, and the common complaint is lock-in to Google's proprietary APIs.
Free tier quotas
Monthly active users
50K on the no-cost Spark plan
SAML and OIDC users
50 monthly active users
Payment method
Not needed for Spark
Phone authentication
Not available on Spark. Billed per SMS on the Blaze plan
Address verification emails
1,000 a day on Spark
Password reset emails
150 a day on Spark
Email-link sign-in emails
5 a day on Spark
Sign-in links
20,000 a day on Spark
Blaze plan
Still no-cost up to 50K MAUs, then Google Cloud pricing. Eligible accounts can get $300 in free credit
Last sniffed Oct 18, 2026. Always confirm on the official pricing page.
👍 Good boy
+Spark gives 50K monthly active users with no payment method needed, so you can ship and test without a card on file.
+On Blaze, the first 50K MAUs stay no-cost and usage above that follows Google Cloud Identity Platform pricing, so there is a documented upgrade path.
+It pairs with the rest of Firebase and Google Cloud, which suits apps that already use those products.
+A Capterra reviewer titled their review as a backend-as-a-service that is easy and affordable to get started, and a Reddit commenter said a fully managed auth service beats rolling your own.
+Higher SMS limits are available by upgrading to Google Cloud Identity Platform, per the limits page.
+Quota increases can be requested from Firebase support with at least two weeks notice, per the limits page.
👎 Watch out
−Phone authentication is not available on Spark, so SMS sign-in needs the pay-as-you-go Blaze plan and is billed per SMS.
−Spark's daily email caps are low for some flows: 150 password reset emails and only 5 email-link sign-in emails a day.
−Firebase Authentication SMS is capped at 3,000 sent a day, and the limits page says you need Identity Platform for higher SMS limits.
−Vendor lock-in is the common review complaint. A G2 reviewer called it real and said migrating away can be expensive, and a Capterra reviewer said most features use proprietary Firebase APIs. Both reviews cover Firebase overall.
−SAML and OIDC sign-in is limited to 50 monthly active users on Spark, so enterprise SSO testing runs out quickly.
−A Capterra reviewer said it is hard to work out how to write the rules once you need more than simple authentication. A commenter in an r/Firebase thread on enterprise use said Firebase has limits unless you buy the Blaze plan.
The catch
The 50K MAU allowance is real, and Spark needs no payment method. The catch is in the details. Phone authentication is not available on Spark, SAML and OIDC are limited to 50 monthly active users, and email limits are low: 150 password reset emails and 5 email-link sign-in emails a day.
Moving to Blaze keeps the first 50K MAUs at no cost and raises the email caps, but it requires a billing account, and SMS is billed per message at Google Cloud rates. Firebase Authentication SMS is capped at 3,000 a day unless you upgrade to Identity Platform.
Independent reviews I found cover Firebase overall and flag lock-in to proprietary APIs. I could not confirm commercial-use terms for Spark from the pages I read.
What’s included
✓Email and password sign-in
✓Email-link sign-in
✓Phone authentication on Blaze
✓Social and federated sign-in
✓SAML and OIDC (50 MAUs on Spark)
✓Client SDKs for web and mobile
✓Upgrade path to Google Cloud Identity Platform
✓Quota increases on request
Free tier value
Generosity
A
Estimated value
50K monthly active users with no payment method
Feature parity
Blaze raises email limits and enables phone authentication, billed per SMS.
No-cost up to 50K MAUs, then Google Cloud Identity Platform pricing. Phone authentication is billed per SMS. Eligible accounts can get $300 in free credit.
Identity Platform upgrade
Removes the Firebase Authentication SMS daily cap and gives higher SMS limits, per the limits page. Rates are on the Google Cloud pricing page.
Common questions
Is Firebase Authentication free?
On the no-cost Spark plan the pricing page lists 50K monthly active users with no payment method needed.
Does phone sign-in work on Spark?
No. The pricing page lists phone authentication as not applicable on Spark and billed per SMS on Blaze.
How many password reset emails can I send?
150 a day on Spark and 10,000 a day on Blaze.
What happens past 50K users?
On Blaze, usage above 50K MAUs follows Google Cloud Identity Platform pricing.
What do reviewers complain about?
Mainly vendor lock-in and rules that are hard to learn beyond simple authentication. The reviews I found cover Firebase overall.
Change history
Checked October 22, 2026
Pricing page and limits page read. G2 and Capterra review excerpts cover Firebase as a whole. Reddit threads read as excerpts. Commercial-use terms not confirmed.
