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A good rule of thumb for a good software business is the toothbrush test: Is your product good enough for people to use at least twice a day?

But AI agents are creating a new test, what I’m calling the magic minimum: Can your product periodically deliver enough unexpected value to be irreplaceable, even if users only engage with it once or twice a month?

In the allocation economy, the universe of viable software businesses expands: an entire ecosystem of specialized agents quietly working in the background, earning their keep through occasional moments of delight.

The origins of the toothbrush test

Larry Page created the toothbrush test early on at Google to filter new product bets like Gmail, and acquisitions like YouTube and Android.

It’s useful because it filters for high-upside products. The biggest software businesses are daily habits. They become indispensable tools people reflexively turn to multiple times a day.

This constraint—that great software businesses need to be a daily habit—is driven by human psychology: You only remember things you use a lot.

The toothbrush test constrains the universe of software businesses

This constraint has shaped the entire software industry...

1. The memory limitation problem for specialized tools
2. How AI agents enable the long tail
3. The magic minimum: proactive value without daily use
4. How agents function like professional services
5. Why background utility trumps daily engagement