Best Free Online Developer Tools to Use in 2026
A practical, opinionated list of the best free online developer tools worth using in 2026, organized by category so you can find what you need fast.
Aug 08, 2026
SSL Certificate Checker
Inspect SSL/TLS certificate details of any website including expiry, issuer, SAN, and certificate chain.
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What is an SSL Certificate?
An SSL/TLS certificate is a digital certificate that authenticates a website's identity and enables an encrypted connection. It contains the website's public key, identity information (domain name, organization), validity period, and is digitally signed by a Certificate Authority (CA).
Key Details to Check
- Expiry date — Expired certificates cause browser security warnings
- Subject Alternative Names (SAN) — Lists all domains the certificate covers
- Issuer — The Certificate Authority that signed the certificate
- Signature algorithm — SHA-256 or stronger is recommended; SHA-1 is deprecated
- Key size — RSA 2048+ or ECDSA is recommended
Frequently Asked Questions
What does "Certificate Chain" mean?
The certificate chain (or certification path) lists all certificates from the server certificate up to the root CA. The browser uses this chain to verify that the server certificate was issued by a trusted Certificate Authority. A complete chain typically includes the server certificate, one or more intermediate certificates, and a root certificate.
How often should I check my SSL certificate?
It's recommended to check SSL certificates monthly and set up expiration alerts at least 30 days before expiry. Modern certificates typically last 90 days to 1 year. Regular monitoring prevents unexpected expiration that could cause website downtime and browser security warnings.
What is the difference between SSL and TLS?
SSL (Secure Sockets Layer) is the predecessor of TLS (Transport Layer Security). SSL versions 1.0, 2.0, and 3.0 are deprecated and insecure. TLS 1.2 and 1.3 are the current secure standards. The term "SSL certificate" is still commonly used even though the certificates are used with TLS protocols.
Is my data sent to your server when I check a certificate?
Yes, temporarily. Unlike most tools on this site that run client-side, SSL certificate checking requires a server-side connection to the target host. The hostname you enter is used only to fetch the certificate details and is not stored or logged.
Last updated: 17 Aug 2026
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