An MLS integration partner that looks solid in a sales call can still leave you with stale listings, a compliance notice from your MLS board, or a normalization layer that quietly drops fields you needed. Because MLS data access is governed by contracts and local board rules as much as by technology, evaluating a partner means checking both engineering fundamentals and compliance fluency — retrofitting either after launch is expensive. This checklist is for proptech teams, brokerages, and portal developers vetting a partner for MLS/IDX/VOW data integration.

Before you start

  • [ ] List every MLS board you need coverage for, and confirm the partner has active feeds (not just "can get") for each one
  • [ ] Decide your access-level need: IDX (public display, field-restricted) versus VOW (broader data including sold/expired listings, stricter licensing)
  • [ ] Clarify whether you need direct board-by-board integration or a national aggregator with a normalization layer
  • [ ] Set a compliance owner internally — someone who will own the relationship with each MLS board's rules, not just the technical connection

1. Technical standard and architecture

  • [ ] Confirm the partner builds on the RESO Web API, not legacy RETS — RETS is no longer maintained and creates technical debt on day one
  • [ ] Ask which RESO Data Dictionary version each feed conforms to, and how the partner handles boards still on older schema versions
  • [ ] For multi-MLS coverage, confirm how the normalization layer reconciles schema differences across boards — this is where subtle data loss happens
  • [ ] Ask how OAuth credentials and board-specific agreements are managed at scale if you need coverage across many markets

2. Data licensing and compliance

  • [ ] Confirm the partner holds current, active license agreements with each MLS board in your target markets — not "we can get access"
  • [ ] Clarify field-level display restrictions and attribution requirements per board, and who is responsible for enforcing them in your product
  • [ ] Ask how the partner handles MLS rule changes — some boards update display rules or licensing terms with limited notice
  • [ ] Confirm whether VOW-tier data requires additional consumer registration or authentication flows on your end, and who builds that

3. Data accuracy and latency

  • [ ] For each MLS in your target markets, ask: feed type, update latency, fields included in normalized output, and current operational status
  • [ ] Request documented production performance — accuracy, latency, error rate, uptime — from reference customers with data volume and market mix similar to yours
  • [ ] Ask what happens when a source MLS feed goes down: does data go stale silently, or is there active monitoring and alerting?
  • [ ] Clarify how deduplication and listing-status conflicts (a property showing different statuses across nearby MLSs) are resolved

4. Uptime, support, and contract terms

  • [ ] Get the contractual uptime guarantee in writing — not the marketing number — and confirm what remedy applies if it's missed
  • [ ] Ask for support response-time SLAs broken out by severity, and what "critical" means in their definition versus yours
  • [ ] Confirm what happens to your integration and historical data if the partner loses access to a specific MLS board
  • [ ] Review termination terms and data portability — can you export normalized historical data if you switch providers later?

5. Security and infrastructure

  • [ ] Confirm encryption, access control, and audit logging practices for data in transit and at rest
  • [ ] Ask about redundancy and failover architecture for feed ingestion, not just for the customer-facing API
  • [ ] Confirm compliance posture relevant to your jurisdiction (data residency, DPDP Act obligations if serving Indian markets)

Red flags

  • Partner is vague about which specific MLS boards they hold active licenses with, or claims "coverage" without documentation
  • Still building new integrations on RETS rather than the RESO Web API
  • No documented update-latency numbers per feed, only a general "real-time" claim
  • Uptime guarantee exists only in a sales deck, not the contract
  • No clear answer on what happens to your product if a board relationship lapses

How to use this

Score candidate partners against sections 1–4 using your actual target market list, not a generic feature comparison — MLS coverage and licensing terms vary enough board-to-board that "handles MLS integration" means little without specifics. Keep documentation the partner provides; MLS compliance audits can require evidence of how data is licensed and displayed.

Vetting an MLS integration partner against real licensing, latency, and compliance requirements is exactly the kind of work Syslabs does with proptech and brokerage teams — including building the API integrations and normalization layer when a ready-made feed doesn't cover what you need.