How fast is your T-Mobile connection? Now you can get an honest answer.

T-Mobile doesn't charge customers extra for exceeding their monthly data limits, but it does slow their connection speeds. Under a new agreement between T-Mobile and the FCC, T-Mobile won't keep speed test applications from showing the actual speeds of slowed connections.

T-Mobile is one of the only major US wireless carriers that doesn’t charge customers extra for exceeding a monthly data limit. But it does slow down connection speeds once customers hit a monthly limit – and that slowdown, known as “throttling,” reduces 4G LTE speeds from around 38 Mbps all the way down to 0.1 to 0.06 Mbps.

The only catch: until now, speed test applications were exempted from T-Mobile’s throttling, so a test to see just how slow your connection was would show everything humming along at regular 4G speeds.

Enough T-Mobile customers complained to the Federal Communications Commission about this practice that the FCC began looking into how T-Mobile discloses network information. T-Mobile and the Commission reached an agreement, and on Monday the FCC announced that T-Mobile will be more honest going forward about how fast customer data speeds are, even after those customers have blown through their monthly data limits.

Under the new agreement, T-Mobile will text customers when they’ve reached their monthly high-speed data limit, letting them know that their speed will be reduced for the rest of the month. The text message will include a link to a speed test that will accurately measure a customer’s reduced speed. T-Mobile will also include a speed test app on its smart phones that will return accurate information about reduced network speeds.

This agreement doesn’t cover all speed tests: some applications will still measure T-Mobile’s full network speed potential, rather than an individual subscriber’s throttled connection speed.

Consumer advocacy group Public Knowledge found those omissions troubling, saying in a statement that consumers should be able to test network speeds using whatever application they wish. “If T-Mobile is truly confident that they are managing their network responsibly,” the group said in a statement, “Public Knowledge hopes that they will free their subscribers to test their network connection with an application that they trust, not one that was pre-approved by T-Mobile.”

The agreement between the FCC and T-Mobile is important because it relates to transparency, the only one of the FCC’s three Open Internet principles that survived a Supreme Court ruling earlier this year. While the FCC considers new net neutrality rules, groups such as Public Knowledge have tried to use the transparency rule to ensure that wireless companies are treating consumers fairly. FCC chairman Tom Wheeler sent letters to the four major wireless companies this summer, asking them to reconsider their speed-reduction practices.