Quick: if you searched “What does IDX mean,” you’re probably building or improving a real estate website. IDX real estate integrations let agents and brokers show MLS listings on their own sites. This page explains IDX vs MLS, how IDX works, IDX cost factors, and technical choices from RETS vs RESO Web API so agents, small brokerages and developers can act quickly.
IDX stands for Internet Data Exchange. It’s the policy and technical setup that allows brokers and their authorized agents to display MLS listings on public-facing websites. Think of IDX as broker reciprocity rules plus the data feed that powers searchable property pages for consumers.
IDX grew from MLS rules meant to share listings among brokers. As consumer websites became critical, MLSs codified how listings could be published online, who can display them, and what attribution is required. The goal: broaden exposure for sellers while protecting broker rights and data integrity.
If you run an agent or brokerage website, want to generate buyer leads, or are building a property search app, you need IDX. If you’re a developer integrating MLS data into a consumer-facing site, you need to understand IDX rules and the technical feed options (RETS vs RESO Web API).
The MLS (Multiple Listing Service) is the authoritative database where brokers list properties. IDX is the permitted method for pulling a subset of MLS data and showing it on public websites under MLS and broker rules. MLS = source; IDX = authorized delivery to public sites.
Portals like Zillow and Realtor.com operate under syndication agreements and their own data ingestion rules. IDX is broker/MLS-controlled and usually shows more complete, current data when properly implemented. Portals may enhance listings with consumer-facing features but direct traffic off your site. IDX keeps visitors on your brand-controlled pages.
IDX (public display) vs. VOW (Virtual Office Website): VOWs allow registered users to see more MLS detail after registering; they are not the same as public IDX displays. Broker feeds are full MLS access for brokerages (subject to MLS policy) and may include non‑public broker‑only fields. Know which permission you have—IDX, VOW, or broker feed—before building features.
IDX content comes from MLS data feeds. Participation rules vary: some MLSs require broker opt‑in, others opt‑out. Listings flagged as “opt‑out” (seller requests) or broker‑only won’t appear. Always check your MLS’s IDX policy for required data elements and opt‑out procedures.
Typical delivery methods:
MLSs mandate certain attributions: MLS name, broker attribution, prohibited editing of status/price without flags, and standardized disclaimers. Displays often require clicking through to MLS details or showing the listing agent/broker. Noncompliant displays risk feed removal.
IDX keeps prospective buyers on your site longer, lets you capture leads via saved searches, email alerts, and inquiry forms, and supports conversion-oriented UX like favorite lists and contact prompts.
Indexable property pages improve long‑tail SEO for neighborhoods, addresses, and property types. Properly implemented IDX (server-rendered pages or SEO-friendly APIs) boosts organic traffic and dwell time compared with embedded iFrames.
With IDX you control branding, calls-to-action, market content, and lead routing. That retains traffic and builds an email/CRM audience rather than funneling users to third‑party portals.
MLSs typically require visible MLS attribution, listing broker/agent credits, and sometimes MLS logos. Fonts, placement, and wording can be specified. Follow exactly—small errors are frequent violation causes.
Common prohibitions: removing “active/pending/sold” status indicators, displaying inaccurate price/status, hiding listing agent/broker, or advertising MLS data for non‑authorized users. Don’t allow consumers to see broker-only fields via public IDX.
Sellers can request opt‑outs from IDX in many MLSs; those listings must be excluded. Broker‑only fields or private remarks must never be surfaced on public IDX displays.
Typical steps: confirm broker permission (many MLSs require broker signoff), submit vendor/URL to MLS IDX committee, undergo compliance review, and correct any violations. Lead time varies—expect days to a few weeks.
Pros: fast setup, low developer costs, built-in lead capture. Cons: potential SEO limits, monthly vendor fees, and customization constraints. Popular for solo agents and small brokerages.
Widgets/iFrames are plug-and-play and preserve IDX compliance via vendor hosting. Downsides: poor SEO (content often not crawlable), slower perceived site speed, and less flexible UX.
Direct integration gives full control and best SEO — you pull data into your templates and build indexable property pages. That requires developer resources and familiarity with RETS or RESO Web API (detailed below).
Balancing freshness and performance: many sites cache IDX data and refresh on a schedule (every 15–60 minutes is common). Respect MLS rules about update intervals. Use incremental syncs, conditional requests, and CDN caching to keep pages fast while avoiding stale data.
RETS (Real Estate Transaction Standard) is an older XML-based protocol used to pull MLS data. It’s stable but dated: varied implementations, complex parsing, and inconsistent authentication. Many MLSs are deprecating RETS.
RESO Web API is the modern standard: RESTful endpoints, JSON payloads, OAuth authentication, and standardized schemas that reduce vendor-specific code. Faster development and easier integration with SPA/mobile apps.
If your vendor or MLS still uses RETS, plan migration: audit custom fields, map schemas, and test auth flows. Many IDX vendors now support both, but new projects should prefer RESO Web API where available for long‑term maintainability.
Costs vary: one-time developer setup ($500–$5,000+) for custom integrations; hosted IDX services typically charge $20–$200/month depending on features. Some plugins have yearly licenses. Hosted solutions reduce upfront dev costs but add recurring fees.
Some MLSs charge vendor fees, IDX access fees, or require active MLS membership. Expect $0–$200/month or occasional per-URL vendor registration fees depending on market. Verify with your local MLS.
Typical steps: vendor selection (1–2 weeks), broker approval & MLS registration (1–3 weeks), technical setup (1–4 weeks), compliance review (days to weeks). Small hosted setups can go live in days if approvals are fast; custom builds usually take longer.
Update frequency depends on MLS and vendor: near-real-time to hourly is common; some feeds refresh every 6–24 hours. Delays come from MLS push schedules, vendor sync limits, and caching strategies.
Causes include opt‑outs, mapping errors between MLS fields and your site, feed parsing bugs, or permissions issues. Missing photos often result from rights or feed limitations.
Implement automated checks: compare recent MLS change timestamps, monitor differential counts, and alert on sync failures. Keep an escalation process with your IDX vendor and MLS tech support.
Common capture points: property inquiry forms, saved search signups, and registration walls for enhanced features. Ensure forms are concise and offer clear value (alerts, saved searches).
Most IDX vendors offer native CRM integrations (e.g., Follow Up Boss, HubSpot). Best practices: tag IDX leads, auto-assign by territory or listing agent, set SLA response rules, and track source attribution for ROI.
Confirm your contract: who owns captured leads (you or the vendor)? Ensure GDPR/CCPA compliance when applicable. MLS rules may restrict resale of MLS data; lead data is typically owned by the brokerage/agent who collects it but verify vendor terms.
Widgets speed delivery but usually include vendor branding and limited style overrides. They can clash with site UI and reduce perceived professionalism if styling is inconsistent.
White-label solutions remove vendor logos and let you brand fully (may cost more). Co‑branded options include vendor IDs or “Powered by” links that some MLSs also require.
Focus on simple filters, clear CTAs, mobile-first design, and breadcrumbed neighborhood pages. Make listing pages indexable, include local market content, and keep inquiry forms above the fold on mobile.
Usually an active MLS broker or agent membership (or explicit broker authorization) is required to get IDX access. Some MLSs allow franchised broker access under special rules—check local policy.
IDX policies vary widely. Differences include allowable data fields, image display rules, opt‑out handling, and required disclaimers. Local IDX committees govern many nuances.
If your site monetizes listings, shares data across brands, or integrates broker-only feeds, consult your broker/MLS compliance contact or real estate counsel to avoid contract and liability issues.
Ask vendors for SLA, average sync intervals, uptime history, and references in your MLS. Check community reviews and sample implementations from similar‑sized brokerages.
Watch for long-term auto-renewals, lead ownership clauses, hidden MLS/vendor fees, and limits on domain changes without new fees. Prefer month-to-month or clear annual terms when possible.
Myth: IDX is a lead system on its own. Reality: IDX generates leads but is not a full CRM—integrate IDX with your CRM for nurturing, tagging, and automation.
Truth: IDX refresh frequency depends on MLS and vendor. Expect short delays—real‑time sometimes, hourly commonly, or longer if using cached vendor feeds.
Buyers: IDX sites offer wide MLS coverage—ask your agent if their IDX shows all local MLS listings. Sellers: If you want your listing excluded from third‑party sites, request an IDX opt‑out with your listing broker. Marketers: Use IDX pages to create neighborhood content and capture long-tail search traffic.
SunnySide is a small brokerage seeking more buyer leads without paying portal premiums. They chose a hosted IDX plugin for WordPress, got broker sign-off, registered the vendor with the MLS, and launched searchable property pages with lead capture forms.
Outcome: SunnySide saw a 30% uplift in inbound buyer leads and longer site sessions. Hiccups: initial compliance issues (missing MLS attribution) were resolved in a vendor update. Lesson: allocate time for compliance and testing.
Downloadable checklist: Download PDF checklist (replace with your CMS file link).
Start with your local MLS compliance team for rules and vendor registration. For technical standards, research RESO Web API documentation. For WordPress users, evaluate major IDX plugins and hosted vendors; ask for MLS references.
If you’d like, I can now produce a version of this outline tailored only to developers or only to new agents/brokers, or expand any H2 into a paragraph-by-paragraph content brief with suggested word counts and keyword suggestions. Which would you prefer?
