# Pylon Developer Platform (PDP)

## Docs

- [Borrower Dashboard Element](https://docs.pylon.mortgage/elements/borrower-dashboard/introduction.md): Complete borrower portal for managing in-progress loans
- [Polling for updates](https://docs.pylon.mortgage/elements/borrower-dashboard/polling.md): Monitor borrower dashboard status changes by polling the GraphQL API
- [Setup](https://docs.pylon.mortgage/elements/borrower-dashboard/setup.md): Build the Borrower Dashboard Element into your app
- [Theming](https://docs.pylon.mortgage/elements/borrower-dashboard/theming.md): Customize the appearance of the Borrower Dashboard Element to match your brand
- [Introduction](https://docs.pylon.mortgage/elements/introduction.md): Get started with Pylon Elements - pre-built components for loan applications and borrower dashboards
- [Loan Application Element](https://docs.pylon.mortgage/elements/loan-application/introduction.md): Complete end-to-end mortgage loan application experience
- [Polling for updates](https://docs.pylon.mortgage/elements/loan-application/polling.md): Monitor loan application status changes by polling the GraphQL API
- [Setup](https://docs.pylon.mortgage/elements/loan-application/setup.md): Build the Loan Application Element into your app
- [Theming](https://docs.pylon.mortgage/elements/loan-application/theming.md): Customize the appearance of the Loan Application Element to match your brand
- [Handling authentication](https://docs.pylon.mortgage/elements/setup/authentication.md): Set up backend authentication for Pylon Elements
- [Loading loans](https://docs.pylon.mortgage/elements/setup/loading-loans.md): Understand when to use Loan Application vs Borrower Dashboard Elements
- [Theme reference](https://docs.pylon.mortgage/elements/theme-reference.md): Complete reference for Element theming
- [Assets](https://docs.pylon.mortgage/entity-models/assets.md): Understanding the Asset entity - financial resources used for down payment, closing costs, and reserves
- [Borrowers](https://docs.pylon.mortgage/entity-models/borrowers.md): Understanding the Borrower entity - individuals applying for a mortgage loan
- [Deal](https://docs.pylon.mortgage/entity-models/deal.md): Understanding the Deal entity - the top-level container for mortgage transactions
- [Disclosures](https://docs.pylon.mortgage/entity-models/disclosures.md): Learn how to retrieve disclosure documents and enable borrowers to sign them
- [Entity relationships](https://docs.pylon.mortgage/entity-models/erd.md): Understanding how entities relate to each other is essential for working with the Pylon API. This page provides a high-level overview of the data model and explains the relationships between core entities.
- [Incomes](https://docs.pylon.mortgage/entity-models/incomes.md): Understanding the Income entity - sources of revenue used for mortgage qualification
- [Annual Percentage Rate (APR)](https://docs.pylon.mortgage/entity-models/key-concepts/apr.md): Understanding APR - the total cost of borrowing including fees
- [Automated Underwriting System (AUS)](https://docs.pylon.mortgage/entity-models/key-concepts/aus.md): Understanding Automated Underwriting Systems (AUS) - automated loan decisioning systems from Fannie Mae and Freddie Mac that evaluate loan eligibility and determine if loans can be sold to investors.
- [Change of circumstance](https://docs.pylon.mortgage/entity-models/key-concepts/change-of-circumstance.md): Under TRID, a valid change of circumstance allows a creditor to issue a revised Loan Estimate and reset the tolerance baseline for closing cost fees.
- [Combined Loan-to-Value (CLTV)](https://docs.pylon.mortgage/entity-models/key-concepts/cltv.md): Understanding CLTV - total of all liens secured by the property
- [Day 1 Certainty (D1C) and Asset and Income Modeler (AIM)](https://docs.pylon.mortgage/entity-models/key-concepts/d1c-aim.md): Learn about Day 1 Certainty (D1C) and Asset and Income Modeler (AIM), automated verification programs from Fannie Mae and Freddie Mac that reduce documentation requirements and accelerate loan processing.
- [Debt Service Coverage Ratio (DSCR)](https://docs.pylon.mortgage/entity-models/key-concepts/dscr.md): Understanding DSCR - a metric for investment property qualification
- [Debt-to-Income (DTI)](https://docs.pylon.mortgage/entity-models/key-concepts/dti.md): Understanding DTI ratio - a key metric for loan qualification that measures monthly debt payments relative to income
- [Introduction](https://docs.pylon.mortgage/entity-models/key-concepts/introduction.md): Glossary of mortgage industry terms and concepts
- [Intent to Proceed (ITP)](https://docs.pylon.mortgage/entity-models/key-concepts/itp.md): Understanding ITP - a regulatory requirement that indicates borrower commitment and triggers automatic order-outs
- [Loan-Level Price Adjustments (LLPA)](https://docs.pylon.mortgage/entity-models/key-concepts/llpa.md): Understanding LLPAs - risk-based pricing adjustments applied to mortgage interest rates
- [Loan-to-Value (LTV)](https://docs.pylon.mortgage/entity-models/key-concepts/ltv.md): Understanding LTV ratio - the percentage of property value financed through debt
- [Principal, Interest, Taxes, Insurance, Association (PITIA)](https://docs.pylon.mortgage/entity-models/key-concepts/piti.md): Understanding PITIA - the complete monthly housing payment including principal, interest, taxes, insurance, and association fees.
- [Points vs. rate](https://docs.pylon.mortgage/entity-models/key-concepts/points-vs-rate.md): Understanding the trade-off between upfront points and interest rates
- [Prepayment penalty](https://docs.pylon.mortgage/entity-models/key-concepts/prepayment-penalty.md): Understanding prepayment penalties - fees for paying off loans early
- [Qualified Mortgage (QM) and fee caps](https://docs.pylon.mortgage/entity-models/key-concepts/qualified-mortgage.md): Understanding Qualified Mortgage standards and the points-and-fees cap that limits upfront charges for QM-eligible loans.
- [Rate lock](https://docs.pylon.mortgage/entity-models/key-concepts/rate-lock.md): Understanding rate locks - guarantees that lock in interest rate and points
- [Reserves](https://docs.pylon.mortgage/entity-models/key-concepts/reserves.md): Understanding reserves - liquid assets required to remain after closing
- [Tolerance cure](https://docs.pylon.mortgage/entity-models/key-concepts/tolerance-cure.md): When closing fees exceed TRID tolerance bands, a cure is required. Pylon is responsible for all tolerance cures.
- [TRID (TILA-RESPA Integrated Disclosure)](https://docs.pylon.mortgage/entity-models/key-concepts/trid.md): Understanding TRID - the integrated disclosure rule that requires specific loan disclosures within 3 days
- [Liabilities](https://docs.pylon.mortgage/entity-models/liabilities.md): Understanding the Liability entity - debts and obligations that impact mortgage qualification
- [Loan](https://docs.pylon.mortgage/entity-models/loan.md): Understanding the Loan entity - individual mortgage loan applications within a Deal
- [Overview](https://docs.pylon.mortgage/entity-models/tasks.md): Learn how to retrieve and manage borrower tasks and loan officer tasks, including document uploads
- [Access Letter](https://docs.pylon.mortgage/entity-models/tasks/access-letter.md): Technical specification for the Access Letter (Joint Access Letter) document
- [Foreclosure Letter of Explanation](https://docs.pylon.mortgage/entity-models/tasks/borrower/foreclosure-letter-of-explanation.md): Provide a detailed letter explaining the circumstances surrounding a prior foreclosure to evaluate eligibility and potential extenuating circumstances.
- [Government-Issued Photo ID](https://docs.pylon.mortgage/entity-models/tasks/borrower/government-id.md): Provide a clear copy of the borrower’s current, unexpired government-issued photo identification for identity verification and compliance.
- [Permanent Resident Card (Green Card)](https://docs.pylon.mortgage/entity-models/tasks/borrower/green-card.md): Provide a clear copy of the borrower’s permanent resident card to confirm lawful permanent residency status for mortgage eligibility.
- [Homeownership Education Course Certificate](https://docs.pylon.mortgage/entity-models/tasks/borrower/home-education-course.md): Provide the certificate of completion for an approved homeownership education course when required by special GSE programs.
- [Work Visa Documentation](https://docs.pylon.mortgage/entity-models/tasks/borrower/work-visa.md): Provide a clear copy of the borrower’s current work visa to confirm legal authorization to work and the stability of qualifying income.
- [Delinquent Federal Debt Documentation](https://docs.pylon.mortgage/entity-models/tasks/credit-inquiry/delinquent-federal-debt.md): Provide documentation of any delinquent federal debt to determine loan eligibility and required resolutions.
- [Letter of Explanation for Derogatory Credit](https://docs.pylon.mortgage/entity-models/tasks/credit-inquiry/derogatory-credit-lox.md): Provide a signed letter explaining the circumstances behind derogatory credit events to support underwriting and risk assessment.
- [Judgment Documentation](https://docs.pylon.mortgage/entity-models/tasks/credit-inquiry/judgment-documents.md): Provide complete judgment documentation so the lender can determine required payoff, subordination, or treatment for eligibility.
- [Gift Letter](https://docs.pylon.mortgage/entity-models/tasks/gift-letter.md): Technical specification for the Gift Letter document
- [Letter of Explanation - Address Discrepancy](https://docs.pylon.mortgage/entity-models/tasks/letter-of-explanation-address-discrepancy.md): Technical specification for the Address Discrepancy Letter of Explanation document
- [Letter of Explanation - Credit Inquiry](https://docs.pylon.mortgage/entity-models/tasks/letter-of-explanation-credit-inquiry.md): Technical specification for the Credit Inquiry Letter of Explanation document
- [Letter of Explanation - Employment Gap](https://docs.pylon.mortgage/entity-models/tasks/letter-of-explanation-job-gap.md): Technical specification for the Employment Gap Letter of Explanation document
- [Letter of Explanation - Large Deposit](https://docs.pylon.mortgage/entity-models/tasks/letter-of-explanation-large-deposit.md): Technical specification for the Large Deposit Letter of Explanation document
- [Letter of Explanation - Recurring Withdrawal](https://docs.pylon.mortgage/entity-models/tasks/letter-of-explanation-recurring-withdrawal.md): Technical specification for the Recurring Withdrawal Letter of Explanation document
- [Divorce Decree for Support Obligations](https://docs.pylon.mortgage/entity-models/tasks/liability/divorce-decree.md): Provide the complete divorce decree when support-related liabilities appear, to determine their impact on qualifying ratios.
- [Installment Loan Payoff Demand](https://docs.pylon.mortgage/entity-models/tasks/liability/installment-payoff-demand.md): Provide a payoff statement for an installment loan being paid off at or before closing to confirm post-closing liability status.
- [Lease Agreement for Liability](https://docs.pylon.mortgage/entity-models/tasks/liability/lease-agreement-liability.md): Provide the lease agreement underlying a lease-payment liability to verify terms, balance, and payoff conditions.
- [Mortgage Payoff Demand](https://docs.pylon.mortgage/entity-models/tasks/liability/mortgage-payoff-demand.md): Provide a payoff demand or statement for a mortgage being paid off before or at closing to confirm the exact amount owed.
- [Proof of Liability Paid Off or Paid Down](https://docs.pylon.mortgage/entity-models/tasks/liability/proof-of-paid-off-or-down.md): Provide documentation that a liability has been paid off or significantly reduced so it can be treated appropriately in qualifying ratios.
- [Proof of Payment by Other Party](https://docs.pylon.mortgage/entity-models/tasks/liability/proof-of-payment-by-others.md): Provide evidence that another party has been making payments on a liability so it can be excluded from the borrower’s debt-to-income ratio when permitted.
- [Revolving Account Payoff Demand](https://docs.pylon.mortgage/entity-models/tasks/liability/revolving-payoff-demand.md): Provide a payoff or current statement for a revolving account being paid off at or before closing to confirm balance removal.
- [Separation Agreement for Support Obligations](https://docs.pylon.mortgage/entity-models/tasks/liability/separation-agreement.md): Provide the complete separation agreement when separate maintenance or similar obligations affect the borrower’s liabilities.
- [Source of Funds to Pay Off Liability](https://docs.pylon.mortgage/entity-models/tasks/liability/source-of-funds-to-pay-liability.md): Provide evidence that a liability being paid off before or at closing is satisfied with acceptable borrower funds so it can be removed from qualifying ratios.
- [Student Loan Agreement for Deferred or Unknown Payments](https://docs.pylon.mortgage/entity-models/tasks/liability/student-loan-agreement.md): Provide the student loan agreement when payments are deferred or not reported so the lender can determine an appropriate qualifying payment.
- [Closing Disclosure for Property Sale](https://docs.pylon.mortgage/entity-models/tasks/owned-property/closing-disclosure-sale.md): Provide the final Closing Disclosure for a completed or pending sale to validate net proceeds, payoff of liens, and removal of housing expense.
- [Hazard Insurance for Owned Property](https://docs.pylon.mortgage/entity-models/tasks/owned-property/hazard-insurance-owned-property.md): Provide the current homeowners insurance policy for an owned property (other than the subject property) to support accurate housing expense and risk assessment.
- [HOA Dues for Owned Property](https://docs.pylon.mortgage/entity-models/tasks/owned-property/hoa-dues-owned-property.md): Provide documentation of current HOA dues for owned properties other than the subject property to ensure association fees are included in housing expenses.
- [Lease Agreement for Owned Property](https://docs.pylon.mortgage/entity-models/tasks/owned-property/lease-agreement-owned-property.md): Provide the current lease agreement for an owned property other than the subject property to verify rental income, occupancy, and ongoing obligations.
- [Current Mortgage Statement for Owned Property](https://docs.pylon.mortgage/entity-models/tasks/owned-property/mortgage-statement-owned-property.md): Provide a complete, unredacted mortgage statement for an owned property so the lender can verify the outstanding balance, payment amount, and escrow details.
- [Net Proceeds from Property Sale](https://docs.pylon.mortgage/entity-models/tasks/owned-property/net-proceeds-from-sale.md): Provide documentation of net proceeds from a property sale to support asset sourcing and liability payoff validation.
- [Sales Contract for Pending Sale Property](https://docs.pylon.mortgage/entity-models/tasks/owned-property/pending-sale-sales-contract.md): Provide the executed sales contract for a property the borrower intends to sell, so the lender can validate the pending sale and its impact on housing expense and assets.
- [Property Tax Statements for Owned Property](https://docs.pylon.mortgage/entity-models/tasks/owned-property/property-tax-statements.md): Provide current property tax statements for owned properties other than the subject property to accurately calculate housing expenses and confirm tax status.
- [HO-6 Walls-In Condo Insurance Policy](https://docs.pylon.mortgage/entity-models/tasks/subject-property/condo-ho6-insurance.md): Provide the unit's HO-6 walls-in condo policy to confirm interior coverage where the master policy does not fully cover unit interiors.
- [Condo Master Insurance and CC&Rs](https://docs.pylon.mortgage/entity-models/tasks/subject-property/condo-master-insurance-and-ccrs.md): Provide evidence of the condominium project’s master insurance coverage and governing documents to confirm project eligibility and adequate hazard coverage.
- [Flood Insurance Policy for Subject Property](https://docs.pylon.mortgage/entity-models/tasks/subject-property/flood-insurance.md): Provide the current flood insurance policy for the subject property when it is located in a special flood hazard area.
- [HOA Dues for Subject Property](https://docs.pylon.mortgage/entity-models/tasks/subject-property/hoa-dues-subject-property.md): Provide evidence of current HOA dues for the subject property to accurately calculate the borrower’s housing expenses.
- [Homeowners Insurance Policy for Subject Property](https://docs.pylon.mortgage/entity-models/tasks/subject-property/homeowners-insurance-subject-property.md): Provide the current homeowners insurance policy for the subject property to support [PITIA](/entity-models/key-concepts/piti) calculations and collateral protection.
- [Preliminary Title Report for Subject Property](https://docs.pylon.mortgage/entity-models/tasks/subject-property/preliminary-title-report.md): Provide a preliminary title report for the subject property so the lender can confirm ownership, liens, and any title issues that may affect first-lien position or eligibility.
- [Subject Property Purchase Contract](https://docs.pylon.mortgage/entity-models/tasks/subject-property/purchase-contract.md): Provide the fully executed purchase contract for the subject property to establish key transaction terms for underwriting and closing.
- [Third-Party Validation - Rent-Free Living Arrangement](https://docs.pylon.mortgage/entity-models/tasks/third-party-validation-rent-free-living.md): Technical specification for the Third-Party Validation of Rent-Free Living Arrangement document
- [VOR/VOM Overview](https://docs.pylon.mortgage/entity-models/tasks/verification-of-rent-mortgage.md): Overview of the Verification of Rent or Mortgage document types
- [Land Contract (VOM)](https://docs.pylon.mortgage/entity-models/tasks/verification-of-rent-mortgage-land-contract.md): Technical specification for the Verification of Land Contract document
- [Mortgage (VOM)](https://docs.pylon.mortgage/entity-models/tasks/verification-of-rent-mortgage-mortgage.md): Technical specification for the Verification of Mortgage document
- [Rental (VOR)](https://docs.pylon.mortgage/entity-models/tasks/verification-of-rent-mortgage-rental.md): Technical specification for the Verification of Rent document
- [Vesting Instructions](https://docs.pylon.mortgage/entity-models/tasks/vesting-instructions.md): Technical specification for the Vesting Instructions document
- [Building with AI](https://docs.pylon.mortgage/guides/getting-started/ai-development.md): Leverage AI-ready documentation formats and seamless integrations with leading AI platforms directly from any Pylon docs page
- [Best practices: API security](https://docs.pylon.mortgage/guides/getting-started/authentication/auth-best-practices.md): Guidelines for securing your Pylon API credentials and access tokens.
- [Overview](https://docs.pylon.mortgage/guides/getting-started/authentication/overview.md): Pylon uses OAuth 2.0 Client Credentials to authenticate API requests. This method provides a secure, industry-standard way to access mortgage rate data programmatically.
- [Complete integration guide](https://docs.pylon.mortgage/guides/getting-started/e2e-build.md): Build a complete mortgage origination integration with Pylon. This guide walks you through creating loans, managing borrowers, running underwriting, pricing products, and moving applications through to funding.
- [Introduction](https://docs.pylon.mortgage/guides/getting-started/introduction.md): This guide introduces Pylon's GraphQL API and explains how to build mortgage workflows programmatically.
- [Node query (global object identification)](https://docs.pylon.mortgage/guides/getting-started/node-query.md): Fetch any object by ID with the node root field. Use it to build open-by-ID search (e.g. Cmd+X), efficient polling, deep links, and list-to-detail in Pylon.
- [Appraisal order-outs](https://docs.pylon.mortgage/guides/getting-started/order-outs-and-integrations/appraisal.md): Learn how Pylon's appraisal waterfall works, from appraisal waivers through desktop/hybrid appraisals to full appraisals, and how to track appraisal status.
- [Credit pulls](https://docs.pylon.mortgage/guides/getting-started/order-outs-and-integrations/credit.md): Learn how to properly obtain consent for credit pulls, understand the difference between SOFT and HARD pulls, and implement credit pull workflows with Pylon's waterfall approach.
- [Asset verification](https://docs.pylon.mortgage/guides/getting-started/order-outs-and-integrations/d1c-aim/asset-verification.md): Learn how Pylon automatically verifies borrower assets using Plaid, eliminating manual documentation and bank statement uploads.
- [Income verification](https://docs.pylon.mortgage/guides/getting-started/order-outs-and-integrations/d1c-aim/income-verification.md): Learn how Pylon automatically verifies income and employment using Truv and The Work Number, eliminating manual documentation and borrower logins.
- [Day 1 Certainty & AIM overview](https://docs.pylon.mortgage/guides/getting-started/order-outs-and-integrations/d1c-aim/overview.md): Learn about Day 1 Certainty (D1C) and Asset and Income Modeler (AIM), automated verification systems that eliminate manual data entry and reduce documentation requirements.
- [Order-Outs Overview](https://docs.pylon.mortgage/guides/getting-started/order-outs-and-integrations/overview.md): Learn when and how Pylon automatically orders third-party services like appraisals, title, income verification, and more after receiving Intent to Proceed (ITP).
- [Title order-out](https://docs.pylon.mortgage/guides/getting-started/order-outs-and-integrations/title.md): For title companies integrating into Pylon: write fees directly to the loan file so the Closing Disclosure is accurate. Pylon absorbs tolerance cures.
- [Fixed loan structures](https://docs.pylon.mortgage/guides/getting-started/pricing-optimizations/fixed-loan-structures.md): Get a fixed loan structure (e.g. 90% LTV) by using `MIN_DOWN_PAYMENT` with a `maxLTV` constraint.
- [Full rate sheet optimizations](https://docs.pylon.mortgage/guides/getting-started/pricing-optimizations/full-rate-sheet.md): Show the full rate stack across all products, including eligible structures and ineligible products and structures with their reasons. Includes performance expectations and UI/UX guidance.
- [Most optimal structure](https://docs.pylon.mortgage/guides/getting-started/pricing-optimizations/most-optimal-structure.md): Get the single best loan structure for your objective (e.g. `MIN_PITIA` or `MIN_DOWN_PAYMENT`), with optional per-product breakdown.
- [Overview](https://docs.pylon.mortgage/guides/getting-started/pricing-optimizations/overview.md): Learn how Pylon's programmatic structuring optimizes over thousands of loan structure permutations to find the most optimal structure for borrowers, saving money on out-of-pocket costs and interest over the life of the loan.
- [Pylon Shield](https://docs.pylon.mortgage/guides/getting-started/pylon-shield.md): Comprehensive Representations and Warranties coverage up to $3M per loan
- [Test borrower profiles](https://docs.pylon.mortgage/guides/testing-app/testing-your-app.md): Deterministic sandbox borrowers for testing credit pulls and edge cases.
- [API Reference](https://docs.pylon.mortgage/playground/api-reference.md)
- [GraphQL authentication](https://docs.pylon.mortgage/playground/authentication.md): Learn how to authenticate GraphQL requests with the Pylon API
- [Document uploads and downloads](https://docs.pylon.mortgage/playground/document-uploads-downloads.md): Learn how to upload and download documents using REST endpoints, since GraphQL doesn't support file operations
- [Error handling](https://docs.pylon.mortgage/playground/error-handling.md): Learn how to handle errors in GraphQL queries and mutations
- [Forming calls with GraphQL](https://docs.pylon.mortgage/playground/forming-calls.md): Learn how to structure GraphQL queries and mutations for the Pylon API
- [Introduction to GraphQL](https://docs.pylon.mortgage/playground/graphql-introduction.md): Learn the basics of GraphQL and how to use it with the Pylon API
- [Using pagination in the GraphQL API](https://docs.pylon.mortgage/playground/pagination.md): Learn how to paginate through large result sets in the Pylon GraphQL API
- [Using GraphQL clients](https://docs.pylon.mortgage/playground/using-clients.md): Learn how to use GraphQL client libraries with the Pylon API
- [Variables and fragments](https://docs.pylon.mortgage/playground/variables-fragments.md): Learn how to use variables and fragments to make your GraphQL queries more reusable
- [Featured examples](https://docs.pylon.mortgage/recipes/featured-examples.md): Explore featured examples to get started with Pylon's API
- [Tracking loan updates](https://docs.pylon.mortgage/recipes/loan-updates.md): Monitor loan changes by polling the GraphQL API
- [Marketing rates](https://docs.pylon.mortgage/recipes/marketing-rates.md): Display competitive mortgage rates on your website alongside APOR (Average Prime Offer Rate) to demonstrate your competitive advantage for creditworthy borrowers.
- [Prequalification](https://docs.pylon.mortgage/recipes/prequalification.md): Determine maximum affordability across all products with just 8 pieces of information. This asynchronous endpoint validates against all guidelines and pricing to find the highest loan amount a borrower can qualify for.
- [Pricing scenarios](https://docs.pylon.mortgage/recipes/scenarios.md): Show borrowers real-time pricing scenarios before creating a loan application. This stateless endpoint evaluates thousands of loan structures against live rates and guidelines.

## OpenAPI Specs

- [openapi](https://docs.pylon.mortgage/api-reference/openapi.json)


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