SEATTLE — It’s one of the oldest tricks in an internet company’s playbook. Concoct a tool that gives the public new statistics on something — the quality of a restaurant or a toaster, say. Then watch visitors flock to the data and worry about accuracy later.

Few such tools have been as controversial as ones that show people the market value of homes, using software algorithms to do the estimates. Homes are typically people’s most valuable asset, so emotions run hot when these estimates are seen as too high or too low.

The best-known of these tools — the Zestimate, from the online real estate website Zillow — began on the internet 11 years ago and has since amassed a huge audience of homeowners, shoppers and nosy neighbors. Sellers say unfair Zestimates can kill offers on their homes. About 171 million people visit Zillow each month, according to the company.

The good news is that the overall accuracy of these home estimates appears to have improved significantly over time. But they continue to have meaningful error rates compared with actual home sale prices. That means that they shouldn’t be used as more than a conversation point between homeowners, shoppers and their real estate agents when they’re coming up with listing prices and offers for homes.