Fetch weekly average mortgage rates from the Freddie Mac PMMS (Primary Mortgage Market Survey) published each Thursday at noon ET; rates are available as a downloadable dataset from freddiemac.com/pmms and through third-party aggregators that provide JSON/CSV APIs
For real-time or daily rate data, integrate with a mortgage rate aggregator API such as Mortgage News Daily or a bank/lender rate feed if available through your lending partner
Calculate monthly principal and interest payment using the standard amortization formula: M = P[r(1+r)^n] / [(1+r)^n - 1], where P is loan amount, r is monthly rate, and n is term in months
Compute the required gross income for affordability by applying a target front-end debt-to-income ratio (typically 28%) to the estimated PITI (principal, interest, taxes, insurance) payment
For loan product eligibility pre-checks, use the Freddie Mac Affordable Check API at sf.freddiemac.com/tools-learning/apis to assess Home Possible and HFA Advantage eligibility before full LPA submission
Present affordability outputs with a disclosure that rates are estimates and actual rates depend on credit score, down payment, and lender pricing at the time of application
Known gotchas
The Freddie Mac PMMS reflects weekly averages for conforming purchase loans and lags real-time market rates; do not present PMMS rates as current pricing — use them as a benchmark only
Freddie Mac's lender-facing APIs (Pricing, Committing, Affordable Check) require a Freddie Mac seller/servicer relationship and are not accessible to general developers
Affordability calculations that omit property taxes, homeowners insurance, HOA dues, and PMI will significantly understate the true monthly cost and borrower qualification threshold
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