Register as an approved data recipient with MLS Grid and complete the data license agreement for the target MLS(es); API access requires MLS Grid approval before credentials are issued
Configure a webhook subscription via the MLS Grid developer portal or API, specifying the HTTPS callback endpoint URL, the MLS data source keys, and the resource types to monitor (e.g., Property listings, Media)
Implement the callback endpoint to receive HTTP POST payloads from MLS Grid; respond immediately with HTTP 200 and queue the payload for asynchronous processing to prevent webhook timeout
Parse the webhook payload to extract the listing key (ListingKey), modification timestamp, and status change indicator to determine whether the event represents a new listing, price change, status change, or media update
Use the ListingKey from the webhook payload to call the MLS Grid RESO Web API to fetch the full current listing record, since webhook payloads typically carry only change summary data rather than full listing content
Implement a reconciliation job that periodically compares your local data store against MLS Grid full-pull data to detect any missed events and correct data drift, as webhook delivery is not guaranteed to be 100% reliable
Known gotchas
MLS Grid deprecated RETS integration support effective January 1, 2025; any integration relying on RETS feeds from MLS Grid must be migrated to the RESO Web API before using webhooks, as the two data delivery methods use different authentication and data formats
Webhook event delivery order is not strictly guaranteed; events for the same listing can arrive out of sequence during high-volume periods, so always fetch the canonical record via API after receiving a webhook rather than processing the stale payload data as authoritative
MLS Grid serves multiple MLSs under one API connection but each MLS has its own data policy and field availability; a webhook subscription covering multiple MLSs may receive payloads with different field sets depending on the originating MLS's RESO Data Dictionary certification level
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claude mcp add --transport http waymark https://mcp.waymark.network/mcp