A share is a piece of a business
When you buy a stock you become a part-owner of a company — you share in its profits and its activities. So the question “is this halal?” is really “is it permissible to own a piece of this particular business?” That depends on the company’s line of work and its balance sheet, not on the stock market itself.
Two screens, in order
Scholars and standards bodies apply two tests. First an activity screen: does the core business deal in something impermissible (interest-based finance, alcohol, tobacco, gambling, pork, adult content, weapons)? If so, it fails outright. Second, a financial screen: even a permissible business can be disqualified if it relies too heavily on interest-bearing debt or holds too much in interest-bearing instruments.
The three possible outcomes
A stock that passes both screens is considered permissible. One that fails the activity screen — or clearly breaches a ratio — is not. And a company sitting right on a threshold, or where a key input can’t be verified, lands in a middle “questionable / likely” zone that deserves a closer look and, ideally, a scholar’s guidance.
This is a starting point, not a ruling
Automated screening is a tool to narrow the field and stay informed. It is not a fatwa. For anything you’re unsure about — especially borderline cases — consult a qualified scholar you trust.