Have you ever overpaid for a beer? Matt Cortland has, and it set him on a path to never repeat the mistake.

That is, for Cortland’s drink of choice: a pint of Guinness. After paying €7.80 (about $8.93) for Irish dry stout at a pub in Dublin earlier this month, the 37-year-old grew curious about the average cost of a pint across Ireland.

To his astonishment, the country’s Central Statistics Office had dropped price tracking of the nation’s most popular beer in 2011. That led Cortland to the wild idea of tracking the price himself.

Cortland—founder of an AI startup—turned to AI to lend him a hand, and a voice. He devised Rachel with AI voice generation platform ElevenLabs. Made as an homage to Rachel Duffy, the winner of the U.K. version of the reality TV show The Traitors and equipped with a Northern Irish accent, the voice-enabled AI agent made more than 3,000 calls across the island, inquiring about the price of a pint of Guinness.

“I was like, ‘Well can I just call every pub in Ireland and conversationally ask them with AI?,’” Cortland told Fortune. “I pulled the thread, and I just kept pulling the thread, and here we are.”

Using the data accrued from the thousands of phone calls, he then turned to Anthropic’s Claude to devise the “Guinndex,” which he calls a “living, breathing” consumer price index for a pint of Guinness across Ireland. It also allows bartenders and beer drinkers to contribute and modify prices.

Now Cortland can see how his €7.80 pint weeks earlier matches up with the rest of Ireland. On Monday, the average price was about €6.01 (about $6.88) and the most common price was €5.50 ($6.30).

Guinness parent company Diageo didn’t respond to Fortune’s requests for comment. Beer prices are independently set by pub owners across Ireland.

AI models are advancing at an increasingly rapid pace, surpassing benchmarks even the most sophisticated scientists deemed out of the realm of the machine. And while many shudder at the idea of an AI job apocalypse, others are leveraging the technology to answer complex questions. Some have even used it to sell their home.

And while OpenAI CEO Sam Altman and Google president Ruth Porat think the technology will solve the world’s most complex issues like finding a cure for cancer, AI is also solving smaller, albeit still important, problems along the way.

Rachel, Cortland’s AI agent, is one of a growing number of voice AIs that are appearing on the other end of your phone line. Data from voice AI firm Regal showed that customers are finding the AI as credible as humans.

Based on data from millions of calls with voice AI agents, people are taking 14% more time to chat with AI than they would with a human representative. They’re also giving 22% longer responses, sharing details they’d normally skip.

Cortland said he saw similar results. The conversations his AI had across Ireland showed that most didn’t realize they were communicating with AI. The transcripts of some of those conversations, reviewed by Fortune, make that clear.

“The cost of a pint of Guinness? Twenty-five pounds. But if you’re coming in for a wee drink, I’ll give it to you for a fiver,” a bartender at Doogies in Enniskillen, Northern Ireland, told Rachel.

“Listen, they’re normally 6.20 [euros], but if you can’t afford one, we’ll buy you one. We’ll look after you,” a bartender at Malzards Pub in Kilkenny, Ireland, told the AI.

While the Guinndex hasn’t yet led to a dramatic price shift, Cortland said he has already seen it yielding results. In one instance, he said a pub owner reportedly lowered the cost of his Guinness by 0.40 euros and then updated the entry on the Guinndex himself.

Cortland’s hoping to replicate the success of the Guinndex for other products, perhaps for prescription drugs in the U.S., where he is originally from, or even for a slice of pizza in New York City.

For Cortland, the level of transparency is essential in a market where he has seen prices fluctuate wildly, sometimes by nearly 2 euros, between pubs located literally 100 yards away from one another.

“If you’re charging €11 for a pint of Guinness, that’s fair enough,” he said. (The priciest pint in Ireland is €11, according to the Guinndex.) “But people should know that information.”