The Karma browser extension runs the same free checkers from a Chrome popup: authority, age, expiry, spam score, backlinks, anchor text, DNS, WHOIS, cache, page count, and traffic.
Sign in once and the popup shows the email on the account, the plan, and the credit balance. Checks follow the free tools: the first 10 domains each day are free, then 1 credit per domain. Purchased credits do not expire.
On Google, Bing, and DuckDuckGo the extension still shows domain age and Karma Metric next to each result.
Add it from the Chrome Web Store.