WATCHING money drain from your bank account has never been so much fun. On WhatsApp, a messaging service ubiquitous in India, sending rupees is now as easy as posting a selfie. Set-up is a breeze, because all Indian banks have been corralled onto a common payment platform on which anyone, from Google and Samsung to local payment firms and banks themselves, can build their own user interface. Money zips instantly from one bank account to the other, without any need to set up a pesky digital wallet or download some new app. At least outside China, there is no simpler way to shift money today.

WhatsApp’s offering is being rolled out gradually. The number of transactions routed through the Unified Payment Interface (UPI), the system on which WhatsApp and the rest are riding, has soared from almost nothing in early 2017 to over 150m a month in January. On current trends, UPI transfers will overtake cash withdrawals from banks within weeks. Some 665bn rupees ($10.2bn) will have shifted hands—or phones—in the year to March.

All this is good news for tech-savvy Indian citizens. It is even better news for the taxman. Electronic transactions, unlike those in hard currency, leave a digital trail that makes it harder to do business informally. Just as an Uber driver cannot hide his income in the same way as a cash-in-hand cabbie can, money routed through bank accounts is easier to track, trace and tax. That is helpful because pushing more of the Indian economy out of the shadows, where perhaps half of all activity takes place, and onto the authorities’ radar has been a central policy of Narendra Modi, the prime minister.

Informality has long been the norm in India. Economists estimate that nine in ten workers toil in the grey economy (recent research from the finance ministry suggests the figure may be somewhat lower). Informal outfits, often small, employ two-thirds of all manufacturing workers, at far lower pay than in formal manufacturing jobs. The informal sector remains the employer of last resort. So Mr Modi’s claim that widespread formalisation would be akin to turning “an old civilisation into a modern society” is no overstatement.

As so often in India, data are patchy. But Mr Modi can claim some success. A new Goods and Services Tax (GST) introduced in July has boosted the number of firms registered to pay indirect taxes by 50%, to nearly 10m. This has become the most serious challenge to those looking to do business under the radar. It subsumed a plethora of nationwide and state taxes adding up to 40% of India’s total take. A sort of value-added tax, it compels businesses to declare both their purchases and their sales if they are to qualify for tax refunds. Plenty of loopholes have been built in, and lots of features have had to be delayed because of IT problems. But the miseries of implementation—and the nearly two decades of political bickering it took to get GST passed—should yield more gain than pain.

That is more than can be said for “demonetisation”, which in November 2016 compelled Indians to trade or deposit most of their cash holdings at banks before their notes turned to worthless pieces of paper. It led to the abrupt withdrawal of 86% of all bank notes from circulation. Only now is currency in circulation, which some see as a proxy for informality, creeping up to previous levels even as the economy has grown (see chart).