King County Property Tax Appeal

Build a filing-ready property tax appeal packet for any King County, WA residential property — the same deliverable contingency services like Owlue and Ownwell charge 25% of first-year savings for.

What it does

Given a residential property address, the pipeline:

1. Resolves the parcel — address → PIN via King County ArcGIS
2. Pulls assessed values — current assessment, land/improvement split, building characteristics, levy rate
3. Finds comparable sales — arm's-length sales within ±18 months, filtered by location, size, grade
4. Adjusts each comp — time, living area, grade, age, bedrooms, bathrooms → adjustment grid
5. Tests the case — is there an over-assessment? How much would you save?
6. Builds the packet — pre-filled petition fields, evidence narrative with comp grid, filing deadline

Quick start

# Clone
git clone https://github.com/chaoz23/king-county-property-tax-appeal.git
cd king-county-property-tax-appeal

# One-time: download King County data extracts (~180MB download, ~880MB on disk)
bash scripts/setup.sh

# Run for any King County address
bash scripts/run_appeal.sh "1817 Morris Ave S, Renton, WA 98055"

Output lands in run/<PIN>/:

• petition.json — pre-filled eAppeals petition fields
• evidence_packet.md — comp grid, adjustments, opinion of value
• deadline.md — filing rule and exact deadline when the notice mailing date is known
• decision.json — go/no-go with savings estimate
• Plus: subject.json, comps.json, valuation.json, parcel.json

As a Claude Code skill

Drop this repo into your Claude Code skills directory and it triggers on:

• "Appeal my property tax"
• "Is my assessment too high?"
• "How much could I save by appealing?"
• Any King County address + a question about property value

Requirements

• Python 3.10+
• Network access to kingcounty.gov and gismaps.kingcounty.gov
• ~1GB disk for the KC assessor data extracts (downloaded automatically)
• No API keys, no paid services, no dependencies beyond Python stdlib

How it works

The appeal is built on the sales comparison approach — the same method the assessor uses. For each comparable sale, adjustments account for how the comp differs from the subject (size, grade, age, bedrooms, bathrooms). The adjusted prices form a range; the opinion of value is the conservative low end.

The pipeline uses only admissible evidence per WAC 458-14-056(5). It deliberately excludes everything the Board of Appeals cannot consider: assessment-to-assessment comparisons, tax increase percentages, personal hardship, or the dollar amount of tax.

Data sources

All public, no API keys needed:

Data	Source	Method
Address → PIN	ArcGIS ParcelAddress geocoder	REST query
Assessed values	eRealProperty Dashboard	HTML parse
Building characteristics	eRealProperty Dashboard	HTML parse
Levy rate	eRealProperty levy distribution	HTML parse
Comparable sales	KC Assessor data extracts	Local CSV
Filing deadline	KC notice mailing schedule	Published by area

Example output

1817 Morris Ave S, Renton WA 98055 (PIN 7222000353):

Assessed:        $536,000
Opinion:         $491,000
Over-assessment: $45,000 (8.4%)
Est. tax saving: $476/year
Deadline:        July 28, 2025

Comp grid: 8 arm's-length sales, adjusted range $439K–$635K
Strongest comps: 1.8% and 2.9% gross adjustment

Disclaimers

• Not legal or tax advice. Decision-support and document preparation only.
• Estimates until validated. Confirm against the actual valuation notice and certified tax roll.
• Owner owns the filing. The property owner is responsible for accuracy and meeting the deadline.
• No outcome guarantee. ~25% of KC appeals receive a reduction.

License

MIT