Sign up for an ATTOM API key at the ATTOM developer portal and review the endpoint documentation for the property detail and AVM resources.
Look up a property by address using the property/basicprofile or property/detail endpoint, passing street address and zip code as query parameters to retrieve the ATTOM property identifier.
Call the AVM endpoint (e.g., avm/detail) with the ATTOM property ID to retrieve the automated valuation, confidence score, and high/low value range.
Retrieve tax assessment history from the assessment endpoint to get assessed value, tax year, and annual tax amount.
Parse the JSON response; ATTOM wraps all responses in a status object — check status.code equals 0 before processing the payload.
Cache results with a TTL appropriate to your use case (AVM data is typically refreshed monthly; tax data annually).
Known gotchas
ATTOM coverage varies by county; rural properties and some states have sparse or absent AVM data — always check the confidence score before displaying the estimate.
The ATTOM API uses its own property identifier (attomId) which does not map directly to APN or parcel IDs without a lookup step.
API plans are tiered by call volume and data depth; sandbox keys return limited or anonymized data that does not reflect production response shapes.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp