How We Built a Property Comps API Covering 11 Global Markets
Property comparable sales data is fragmented. Every country has its own government registry, its own data format, its own quirks. If you are a proptech company, real estate investor, or AI agent that needs comps across multiple markets, you are looking at 11 different integrations.
We unified all of them into one REST API.
The Markets
| Market | Source | Transactions | App |
|---|---|---|---|
| United Kingdom | HM Land Registry | 31M+ | property.nwc-advisory.com |
| France | DVF / DGFiP | 8.3M+ | property-fr.nwc-advisory.com |
| New York City | NYC Dept of Finance | 51K+ | property-nyc.nwc-advisory.com |
| Singapore | data.gov.sg (HDB) | 973K+ | property-sg.nwc-advisory.com |
| Dubai | Dubai Land Dept | 1.3M+ | property-dxb.nwc-advisory.com |
| Chicago | Cook County | 180K+ | property-chi.nwc-advisory.com |
| Miami | Miami-Dade County | 81K+ | property-miami.nwc-advisory.com |
| Philadelphia | City of Philadelphia | 48K+ | property-phl.nwc-advisory.com |
| Connecticut | CT Open Data | 155K+ | property-ct.nwc-advisory.com |
| Ireland | Property Price Register | 27K+ | property-ie.nwc-advisory.com |
| Taiwan | Ministry of Interior | 23K+ | property-tw.nwc-advisory.com |
Architecture
Each market runs its own FastAPI backend with a local SQLite database. A unified gateway at api.nwc-advisory.com routes requests by the market parameter to the right backend:
GET /v1/comps?market=nyc&zip_code=10001&limit=10&months=12 GET /v1/stats?market=uk&postcode=SW1A1AA GET /v1/trends?market=fr&code_postal=75001
The gateway normalizes responses into a consistent schema regardless of which market you query. Every response includes the same fields: price, date, address, property type, area, and price per unit.
Why Government Data
Every transaction in our database comes from an official government registry. This matters because:
- Complete coverage - Government registries record every sale, not just listed properties.
- Verified prices - These are actual transaction prices, not asking prices or estimates.
- No licensing fees - Public data means we can offer a free tier.
- Regular updates - Most registries update monthly.
The Hard Parts
Location parameters differ by market. UK uses postcodes (SW1A1AA), France uses code postal (75001), NYC uses ZIP codes (10001), Dubai uses area names (Dubai Marina). The gateway auto-detects which parameter to route based on the market.
Database performance at scale. The UK database has 31 million rows in an 8.7GB SQLite file. A radius search around a dense postcode like Norwich NR1 used to take 168 seconds. Compound indexes on (postcode, property_type, date DESC) brought it down to under 5 seconds.
Currency and unit normalization. UK reports price per square foot, France uses price per square meter, Singapore uses price per square foot but in SGD. The API returns raw local values plus a normalized price_per_unit field.
AI Agent Integration
We also built an MCP server so AI agents (Claude Desktop, Claude Code) can query property data directly. The server exposes three tools:
search_property_comps- Find recent sales near a locationget_area_stats- Market statistics for an arealist_markets- All available markets
Free tier: 50 requests/month, 10 results per search. No credit card required.
About NWCA
New Way Capital Advisory builds financial analytics tools for wealth managers and investors. Beyond property comps, our platform includes:
- Portfolio X-Ray - Free fund look-through analysis
- Portfolio Consolidation - Multi-custodian portfolio merge with bilingual PDF reports
- MomentumFlow AI - AI stock scanner with transparent risk signals
- Portfolio Analyser - Institutional portfolio analysis with audit trail