Talk about an impulse buy: Twitter unveiled its long-awaited ecommerce platform today — enabling users to buy products directly from a tweet —  sending shares up 3.7% in mid-day trading. The test will begin with “a small percentage of U.S. users” via their Android and iOS mobile apps and will grow, the company says in a blog post. They’ll see a “Buy” button on some messages : If they click on it, then they’ll see additional product info and a prompt to enter shipping and payment data. Twitter will confirm, encrypt and store them so they can be reused for subsequent transactions. Sellers won’t see the credit card number without the user’s permission, and users can remove the payment data from their account when they want.

“This is an early step in our building functionality into Twitter to make shopping from mobile devices convenient and easy, hopefully even fun,” says Group Product Manager Tarun Jain. Twitter plans to offer deals that users “can’t get anywhere else” and enable sellers to “turn the direct relationship they build with their followers into sales.”

The initiative could help Twitter to renew investor faith in its growth prospects. Shares are down 17.8% in 2014 amid concerns that the company will find it hard to persuade advertisers that sponsored tweets pay off  — and that the platform is too complicated to attract many non-users.

Twitter’s test will use social buying platforms from Fancy (@fancy), Gumroad (@gumroad), Musictoday (@Musictoday) and Stripe (@stripe). The initial merchandise includes releases from musicians including Brad Paisley, Demi Lovato, Eminem, Keith Urban, Megadeth, Pharrell, and Wiz Khalifa . Others offering products include Burberry and The Home Depot. Users also will be able to make transactions with nonprofits including DonorsChoose, GLAAD,  Global Citizen, and  The Nature Conservancy.