wss-backup.slack.com isn't a typical website you browse to shop or sign up. It's a simple technical endpoint that Slack uses to let people verify their network can connect to Slack's services. The page literally says someone from Slack asked you to load it — and if you're reading this, the test worked.
Because it's a Slack subdomain, the identity and reputation signals are strong. Slack (owned by Salesforce) operates this, and the site has been around for years with a clean security record. There are no privacy policies or contact forms, but that's normal: this page isn't collecting your data or processing payments.
If you came here wondering "is wss-backup.slack.com a scam?", the short answer is no. It's a legitimate part of Slack's infrastructure. The only thing it does is tell you whether your connection is working. You don't need to worry about safety — just follow whatever instructions your Slack admin or support team gave you.