Let's Encrypt Explained: How Free SSL Certificates Work
March 1, 2026 - 9 min read
Let's Encrypt has fundamentally changed the SSL certificate landscape. Since its public launch in 2015, this free, automated, and open Certificate Authority has issued billions of certificates and helped push HTTPS adoption past the 95% mark.
What Is Let's Encrypt?
Let's Encrypt is a free, automated, and open Certificate Authority (CA) operated by the Internet Security Research Group (ISRG), a California-based nonprofit organization. ISRG's mission is to reduce financial, technological, and educational barriers to secure communication on the internet.
Let's Encrypt is sponsored by major technology companies including Mozilla, Google, Cisco, and the Electronic Frontier Foundation.
How the ACME Protocol Works
Let's Encrypt uses the ACME (Automatic Certificate Management Environment) protocol, standardized as RFC 8555. The ACME protocol automates three steps: account registration, domain validation, and certificate issuance.
Domain Validation Methods
Let's Encrypt supports HTTP-01 (place a file on your web server) and DNS-01 (add a TXT record to your DNS). DNS validation is required for wildcard certificates.
Certificate Lifetime and Renewal
Let's Encrypt certificates are valid for 90 days. This short lifetime is intentional - it encourages automation and limits the damage from key compromise.
Rate Limits
Let's Encrypt enforces rate limits to prevent abuse: 50 certificates per registered domain per week, 5 duplicate certificates per week, and other safeguards.
Get Started with Let's Encrypt
freesslcert.net provides a web-based interface for generating Let's Encrypt certificates without installing certbot or using the command line.
Generate a Free SSL Certificate