TLS (Transport Layer Security) and its predecessor SSL (Secure Sockets Layer) are cryptographic protocols that encrypt the connection between a user's browser and your web server. When a site uses HTTPS, every piece of data traveling between the two endpoints, login credentials, form submissions, credit card numbers, API responses, is encrypted so that anyone intercepting the traffic sees only scrambled bytes. A TLS certificate, issued by a trusted Certificate Authority, verifies that your server is who it claims to be, preventing attackers from impersonating your domain with a lookalike server. Modern web applications exclusively use TLS 1.2 or 1.3, as older SSL versions have been deprecated due to known vulnerabilities.
Without TLS, every request and response between your users and your application travels in plain text across the internet. That means anyone on the same Wi-Fi network, any compromised router along the path, or any malicious ISP could read usernames, passwords, session tokens, and personal data in real time. Beyond the security implications, Google has used HTTPS as a ranking signal since 2014, and modern browsers display prominent "Not Secure" warnings on HTTP pages, destroying user trust before they even interact with your product. For any application handling sensitive data, TLS is not optional. It is the baseline.
Without TLS, every request and response between your users and your application travels in plain text across the internet.
In 2015, Lenovo shipped laptops pre-installed with Superfish adware that installed its own root certificate, effectively breaking TLS for all HTTPS traffic on those machines. This allowed man-in-the-middle attacks where any attacker on the same network could intercept banking credentials, emails, and private communications. The incident affected millions of users and resulted in a $3.5 million FTC settlement. On a smaller scale, any application served over plain HTTP is vulnerable to session hijacking attacks like Firesheep demonstrated in 2010, where an attacker on a coffee shop Wi-Fi network could take over Facebook and Twitter sessions with a single click. TLS eliminates this entire class of attack.