At some point I realised this should just be an app, and that other people could add spots too. That's Curbie. You drop a pin where you parked, answer a few quick questions about what the rules are, and that information becomes available to everyone. The bit I care about most: it tells you whether a street is free right now based on its operating hours, and if it is paid, how much, so you can see at a glance whether you have to pay before you drive over.
What it doesn't tell you is if a spot is physically available to park or not. Google attempted to solve that problem in 2010 with Open Spot but failed. It is a tough one really.
Curbie is also a utility app, so drivers can use the "Park here" feature after they park, which locks in the GPS coordinates of their car so they never forget where they parked. They can also set a timer to remind them so they never overstay and risk being clamped. Depending on how much time is left on their timer, other users can see an estimate that a driver is about to leave, in 2 minutes for example. You can always turn this feature off if you are concerned about privacy. It's iOS only for now since it's just me building it. To get it off the ground I mapped roughly 100 streets in my city so it isn't a blank map on day one.
Would love feedback, including the brutal kind. Especially curious how people would solve the cold start problem of getting crowdsourced data in a new city.