I bought my first house in Seattle last year. Six months later, King County mailed me a piece of paper telling me it was worth $306,000 more than I paid for it.

Same house. Same tired roof, same list of things I already knew I'd be fixing for years. Nothing about it changed. But according to the county, it quietly appreciated by about a third of a million dollars — because a mass-appraisal model said so.

$1,067,000Last year
$1,373,000This year
📷 Your redacted King County value notice goes here — the one showing the jump. static/blog/value-notice.png
My 2026 King County value notice. "THIS IS NOT A TAX BILL" — but it's the number the tax bill is built on.

I'm a data engineer. I stare at other people's numbers for a living, and I've built enough models to know that a number this clean — a big round jump, no explanation attached — usually means nobody looked at the actual thing. It's an estimate from a computer that has never once stood in my kitchen.

Which is annoying, because my kitchen has opinions. So does the roof, and the thing the inspector circled twice.

📷 A photo or two of the actual problems — the stuff the "value" ignores. static/blog/house-problems.png
The condition the model doesn't see. This is what "worth $1.37M" looks like up close.

My honest first reaction was: who is going to pay that, and why is it me? And to be clear, I love this city. Genuinely. I also write a very large check every year to fund a government whose results are, let's say, not always visible from my front porch. You're allowed to love a place and be furious about how it's run at the same time. Both things can be true. What I'm not willing to do is overpay on a number nobody can defend, just because contesting it sounds like a hassle.

So I stopped being mad long enough to go read the rules. Then I got mad again, but productively this time, and I appealed.

Turns out it's less of a hassle than you'd think — and the whole system is more gameable-in-your-favor than it looks, once you understand it. So I wrote it all down. Read in order, or jump to what you need:

My hearing is July 13. I'll update the appeal post with how it went, numbers and all.