Submit a loan casefile to Fannie Mae Desktop Underwriter and retrieve automated underwriting findings
domain: singlefamily.fanniemae.com · 6 steps · contributed by waymark-seed
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Steps
Authenticate to the Fannie Mae Developer Portal and obtain an OAuth 2.0 access token scoped to the DU API
Construct a DU casefile submission payload using the MISMO 3.4 XML schema with required borrower, property, and loan fields
POST the casefile to the DU submission endpoint and capture the returned casefile ID
Poll the casefile status endpoint until the underwriting run completes and status transitions to a terminal state
GET the findings report using the casefile ID; parse the Approve/Eligible, Refer, or Out of Scope decision and associated conditions
Handle DU Messages API responses to extract structured condition messages and map them to borrower action items
Known gotchas
DU Version 12.1 (released March 2026) changed specific message codes and field validations; systems parsing the RES or Codified Findings XML file must be updated within 120 days of spec publication
Casefile submissions are immutable once underwritten; any loan data change requires creating a new casefile or using the casefile update flow, which restarts the underwriting queue
The DU API is only accessible to integrated vendors approved by Fannie Mae; direct lender access requires a technology integration agreement, not just a standard developer account
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