Clerk
Clerk is a hosted user-management/auth platform from Clerk, Inc. (San Francisco; founded 2019 by Colin and Braden Sidoti), which raised a $50M Series C in October 2025 led by Menlo Ventures and Anthropic's Anthology Fund, pushing total funding past $100M. Pricing is denominated in Monthly Retained Users (MRU), not raw MAU: free tier covers 50,000 MRU; Pro is $25/mo ($20/mo billed annually) with 50k MRU included, $0.02/MRU overage to 100k, plus 1 enterprise SSO connection (extra connections $75/mo, 2-15 tier). The @clerk/javascript SDKs are MIT-licensed — @clerk/nextjs and @clerk/clerk-react each pull well over 1M weekly npm downloads — though the auth backend itself is closed-source SaaS. Latest SDK release: clerk-js 6.25.3 (July 14, 2026). Current version/status: clerk-js SDK 6.25.3 (July 14, 2026); hosted backend is continuously-deployed SaaS, unversioned. License: Proprietary hosted SaaS; client SDKs (@clerk/javascript) are MIT-licensed. Pricing: Free tier 50,000 MRU (monthly retained users); Pro $25/mo ($20/mo billed annually) includes 50k MRU + $0.02/MRU overage to 100k + 1 enterprise SSO connection (extra connections $75/mo, 2-15 tier). Enterprise is custom, annual billing only. Maintained by Clerk, Inc. (San Francisco; $50M Series C Oct 2025 led by Menlo Ventures and Anthropic's Anthology Fund).
Pick Clerk when you're shipping a Next.js/React app fast and want pre-built sign-in/sign-up/profile UI components that don't look like a 2012 form — that's the actual moat, not the auth logic underneath. Skip it once enterprise SSO volume matters: $75/mo per connection past the first stacks up faster than Kinde's Plus plan, which bundles unlimited SSO connections into one flat $75/mo. Clerk's own blog has had to publish standalone explainers just to walk developers through what "Monthly Retained User" billing actually means on their invoice — that's not a good sign for pricing transparency. Known weakness: Billing runs on "Monthly Retained Users" — a returning-user metric distinct from raw MAU that Clerk has had to write dedicated explainer posts to clarify — and enterprise SSO is billed per-connection ($75/mo each) rather than bundled flat-rate like some competitors.
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