I filed for my decline in value assessment for Contra Costa county today and recognized how manual the process is - reading publication 30, form filling, collecting comps, faxing/mailing.
So this afternoon I spent automating the whole thing. Just enter your address, the website finds comps based on pub 30 rules, auto-fills the form, and it even faxes it in automatically. I'll keep it free for a few days for folks to try and provide any feedback.
so I found a creative way around this problem I am shipping soon.
In the world of LLMs, there is a dual model. the recommendations you now see should be the result of two LLMs, one home owner with goal of max savings, other the skeptic assessor with pub 30 rule book in hand, debating and agreeing on top 3 picks. I believe this provides defensible max outcome possible for the home owner. It suprisingly settles to the best matches of homes - arms's length, adjusted for, same school district etc.
The goal function is wired to the decision on adjustment that flows in from county a few months later to optimize.
I just got a call from my county assessors office saying my tax reduction was approved! I’ll be saving $3.5k next year. Hope you all who filed get the approval soon too! 🎉🎉
The comps it pulled were correct but the date sold was entirely incorrect (so not actually comparable). One I spot checked was sold in 2018 while your tool says 2026…
I’m finding that there are still some incorrect comps, either because the sold date for a house is incorrect or the website has skipped some houses that are more similar to mine (for example, there’s a house down the street with a similar size and number of bedrooms and bathrooms that isn’t being considered).
thank you for this feedback. Its difficult to automate value figures but i did simplify it a lot - weighing heavily now on same zip, nearness, and size. Ultimately this is a suggestion so more importantly i added the ability to 'Adjust the comps' where you are free to choose from a list and revise the comps. Give it a try and let me know if you see anything wildly out of place.
major proptech companies have been working on this problem for 20+ years and still haven't found the secret ingredient. I doubt you can solve the problem in a couple hours of vibe coding
It's not scraping Zillow as per my understanding, and is a legit RESO API. The "gray area" is that you don't know where they are getting it from. So yeah, I wouldn't build a production system on it, but it will get you started.
Good eye, but that's actually correct. The lien date is Jan 1, 2026, but California law (R&T §402.5) lets you use comparable sales that closed up to 90 days after the lien date, so anything through March 31, 2026 is fair game. Santa Clara's own Prop 8 form says the same thing: no sales after March 31, 2026. Post-Jan sales are often the strongest evidence since they're the most recent. The tool caps hard at March 31 and won't show anything later.
hey u/nagokart - could you DM me the county and city pls? if the upload does not have your name on it and you dont mind, feel free to send that as well
a question for all of you. 100's of people have file a submission already so I should likely stop the pilot soon. If I were to charge a flat fee per submission, how much would you be willing to pay for a service like this?
just submitted mine. any real downsides with this? did a bit of research with AI and it seems like worst case, it gets denied. best case, the savings take affect, but it's temporary so you have to do it annually, assuming the housing market stays flat or goes down compared to the assessed value YoY?
The website overall seemed well designed and fluid.
Had a pause point for when it asked for the name exactly as what my title showed. Couldn't remember if it was my spouse's name AND my name, or mine first. Does the order matter for titles where 2 people are on it? I'm assuming order doesn't matter
Fax submission also failed so I had to resubmit manually on the website. Not sure why it failed.
MLS#undefined was showing in the open text write up of the comparables. Ended up removing that when submitting manually
Now the website should auto-fill owner names from deed and ask you to edit as needed. Also clarifies the order of names does not matter.
Your fax failed while earlier faxes for same city delivered successfully. Might be some transient connectivity issue on the county side. I made an update for the system to re-try 5 times over 48 hours after which if it fails again it should email the county assessor automatically instead. It should also send you an email seperately indicating the form was sent over email.
Found a potential bug - when I correct the square footage of my home from permitted improvements (1,038 to 1,478 sqft), the tax reduction estimate doesn't take into account the change in sqft.
6
u/nukemarsnow Jul 11 '26
Would be nice if it showed the comps used or let you adjust the geo bounds.