The Seismic Shift In One of North America’s Largest MLSs

At Repliers, we had been preparing for months. The Toronto Regional Real Estate Board (TRREB) had announced their transition from the legacy RETS system to the new PropTx RESO Web API, and we knew exactly what this meant: a fundamental change that would affect every real estate application integrated with their data. While we were well-prepared, many developers across the industry weren’t ready for the ripple effects that would follow the switchover.

Why TRREB Made This Change (And Why It Matters)

For years, real estate technology has operated on a patchwork of systems. Each MLS board maintained its own data structure, field names, and property values. The Real Estate Standards Organization (RESO) emerged to bring order to this chaos, pushing for a standardized data dictionary and delivery mechanism that could work across North America.

TRREB’s migration represents a significant step toward this unified future. The new RESO Web API offers substantial benefits:

• A modern RESTful architecture that’s more efficient than the aging RETS system
• Standardized field names and values that align with other MLS systems
• Better interoperability between different real estate technology platforms

Repliers is RESO member and we support this movement toward standardization. The vision makes perfect sense: a consistent, predictable data structure across all MLS systems would dramatically simplify development and integration.

The Hidden Complications Beneath the Surface

But as with many technological transitions, the devil is in the details. When we began analyzing the differences between TRREB’s legacy RETS system and their new RESO Web API implementation, we uncovered hundreds of small but critical changes that would impact existing applications.

Consider how property types are represented in the two systems:

Old Value (RETS)	New Value (RESO Web API)
Att/Row/Twnhouse	Att/Row/Townhouse
Co-Op Apt	Co-op Apartment
Condo Apt	Condo Apartment
Commercial/Retail	Commercial Retail

These might look like minor spelling adjustments or formatting differences, but to your application’s code, they’re entirely different values. A search filter looking for “Condo Apt” would return nothing in the new system, where that same property is now labeled “Condo Apartment.”

This is just one example among hundreds of similar changes that will silently break applications built on the legacy RETS system.

The impact isn’t limited to property types. Almost every aspect of the data structure has changed:

• Field names follow a different convention
• Enumerated values (like property features, status codes, etc.) have new standardized formats
• Data relationships and hierarchies have been reorganized
• Geographical boundaries and location classifications have been updated

Potential Problems We Anticipated

Without proper preparation, the transition could have been disastrous for our clients. Imagine a boutique real estate team in downtown Toronto whose entire customer portal is built around TRREB’s legacy data structure. Their application features advanced search functionality allowing clients to filter specifically for “Condo Apt” properties within certain neighborhoods.

After TRREB’s transition, without intervention, their search system would return zero results—despite there being hundreds of matching properties in the database. To their clients, it would appear as though the condo market had suddenly disappeared overnight.

Or consider a real estate analytics firm with complex historical trend analysis based on property classifications. When the underlying values changed, their year-over-year comparisons would show artificial drops and spikes that wouldn’t reflect actual market conditions.

These scenarios aren’t theoretical. Every application that directly integrated with TRREB’s RETS system faced these challenges.

How We Solved It: Building a Bridge Between Two Worlds

Well ahead of the transition, our team at Repliers faced a critical decision: we could either ask our hundreds of subscribers to update their applications to work with the new values, or we could build a solution that would shield them from the transition entirely.

We chose the latter approach.

Over several weeks, our development team meticulously mapped every value change between the two systems. We built a transformation layer that automatically converts the new RESO values back to the format that existing applications expect. This reverse-compatibility solution required significant effort on our part, but it demanded zero changes from our subscribers.

The morning the transformation layer went live, our clients’ applications continued functioning exactly as they had before. Search filters returned the expected results. Historical comparisons maintained their integrity. End users never noticed that a massive technological transition had occurred behind the scenes.

What This Means for Your Real Estate Application

If you’ve built an application that integrates with TRREB’s data, you now face a similar choice:

1. Rebuild your integration to work with the new RESO Web API and update all your code to use the new values
2. Create a transformation layer that maps between the old and new values to maintain compatibility
3. Partner with a provider like Repliers who has already solved these challenges

Each approach has its merits depending on your specific situation:

• New applications should absolutely be built on the RESO standard from the ground up
• Legacy applications with limited resources might benefit most from a partnership solution
• Large-scale platforms with dedicated development teams might choose to build their own transformation layers

Moving Forward in a Standardized World

TRREB’s transition to RESO Web API isn’t an isolated event. It’s part of a broader industry shift that will eventually touch every MLS system across North America. The organizations that adapt successfully to these changes will be positioned to benefit from greater interoperability and standardization in the future.

At Repliers, we’re committed to making this transition as seamless as possible for real estate technology developers. Whether you’re building a new application on the RESO standard or adapting an existing system to work with these changes, understanding the full scope of the transition is the first step toward success.

The future of real estate technology is standardized, consistent, and interoperable. The path to get there may be complex, but with the right approach, your applications can navigate this transition without disrupting the agents and clients who depend on them.