MISMO 3.6 XML Explained for Appraisers (No Developer Required)

If you've ever opened an appraisal export and seen a wall of angle brackets, you've met XML. Under UAD 2.6 you could ignore it: your software made a MISMO 2.6 file in the background, glued it to the PDF and you never thought about it again. Under UAD 3.6 you can still avoid editing it, but MISMO 3.6 XML is now the report. The PDF is a picture of it, and the GSEs' compliance rules read the XML, not your PDF. This guide explains what's in the file in plain terms, so the next time a lender forwards a Fatal message you'll know what it's talking about.

Key takeaways

• MISMO 3.6 is the data standard. UAD 3.6 is the GSEs' appraisal dataset built on it.
• The deliverable is a zip: one XML, one matching PDF and an Images folder, 60 MB or less.
• The XML holds every value you entered, labeled with a standard name. The PDF must match it.
• Images are files in the zip. The XML only points to them.
• Compliance rules and UCDP read the XML. A perfect-looking PDF can still fail.

What MISMO is, and why version 3.6

MISMO, the Mortgage Industry Standards Maintenance Organization, publishes the data standards lenders, investors and vendors use to exchange mortgage data. Its standards define names for things (a property's address, a loan amount, a condition rating) so that every system means the same thing by them.

UAD 2.6 was built on an older MISMO version, 2.6. For UAD 3.6, Fannie Mae and Freddie Mac moved to the MISMO 3.6 reference model. The sample files in the GSEs' Appendix D-1 declare it right at the top: MISMOReferenceModelIdentifier="3.6.0366". The GSEs also publish a schema, a set of rules for what a valid file looks like, as part of the UAD 3.6 documents on the Fannie Mae UAD page and the Freddie Mac UAD page.

You don't need to know any of this to appraise. You need to know one thing: the GSEs now read your appraisal as data, field by field, and the file that carries that data is the XML.

What's in the zip

Appendix B-1, the URAR Implementation Guide, describes the package. One zip per appraisal, not more than 60 MB:

Smith_123Main/
  Smith_123Main.xml     the UAD 3.6 data, UTF-8
  Smith_123Main.pdf     the report, rendered from the same data
  Images/
    DwellingFront.jpg
    DwellingRear.jpg
    Street.jpg
    Comp1.jpg
    ...

The rules for each piece, from B-1:

"First-generation" is worth a moment. It means the PDF comes straight from your software. A PDF you printed, scanned, edited in Acrobat or reassembled from pieces isn't first-generation. If you need to change something, change it in the report and rebuild the package.

Watch out: Don't rename or re-zip the package by hand. If the XML points to Images\Comp1.jpg and you renamed the file to comp 1.jpg, the image is missing as far as the XML is concerned. Rebuild from your software instead.

Reading the XML without being a developer

Open a UAD 3.6 XML file in any text editor and you'll see nested labels. Each label is called an element. Elements contain other elements, the way a folder contains folders. At the top is MESSAGE. Deep inside are the parts that matter to you: the properties (the subject and each comp), the valuation, the parties and the images.

Here's a real piece from the GSE's own single-family sample (Appendix D-1, SF1), lightly trimmed. It's the subject's area breakdown:

<PROPERTY_UNIT_AREA>
  <UnitAboveGradeUnfinishedAreaMeasure AreaUnitOfMeasureType="SquareFeet">0</UnitAboveGradeUnfinishedAreaMeasure>
  <UnitBelowGradeUnfinishedAreaMeasure AreaUnitOfMeasureType="SquareFeet">230</UnitBelowGradeUnfinishedAreaMeasure>
  <UnitNonStandardAboveGradeFinishedAreaMeasure AreaUnitOfMeasureType="SquareFeet">0</UnitNonStandardAboveGradeFinishedAreaMeasure>
  <UnitNonStandardBelowGradeFinishedAreaMeasure AreaUnitOfMeasureType="SquareFeet">0</UnitNonStandardBelowGradeFinishedAreaMeasure>
  <UnitStandardAboveGradeFinishedAreaMeasure AreaUnitOfMeasureType="SquareFeet">3002</UnitStandardAboveGradeFinishedAreaMeasure>
  <UnitStandardBelowGradeFinishedAreaMeasure AreaUnitOfMeasureType="SquareFeet">1300</UnitStandardBelowGradeFinishedAreaMeasure>
</PROPERTY_UNIT_AREA>

Read it like a sentence: 3,002 square feet of standard finished area above grade, 1,300 finished below grade, 230 unfinished below grade, and zero nonstandard area, above or below. Notice the zeros. They're written out on purpose. Compliance rules UAD1187 and UAD1484 are Fatal if the nonstandard area fields are missing, "even if the value is 0."

And here's how the sample refers to a photo:

<IMAGE>
  <ImageCategoryType>DwellingFront</ImageCategoryType>
  <ImageFileLocationIdentifier>\\Images\SF1_DwellingFront.png</ImageFileLocationIdentifier>
  <MIMETypeIdentifier>image/png</MIMETypeIdentifier>
</IMAGE>

The photo isn't in the XML. The XML says: there's a dwelling front photo, here's where it is in the zip, and here's its file type. That ImageCategoryType is what lets the rules check that the right photos exist. Rule UAD1274 is Fatal if the required subject photos aren't included. Rule UAD1275 is Fatal if a sales comparable used in the valuation has no photo.

Why the XML matters more than the PDF now

Under UAD 2.6, reviewers mostly read the PDF, and the XML carried a subset of the data. Under UAD 3.6, it flips. The XML carries everything, and three things read it before a person does:

1. The schema. The GSE schema (XSD) defines which elements can appear, in what order and with what kinds of values. An invalid file can fail before any rule runs.
2. The compliance rules. Appendix H-1 lists 728 rules, 592 Fatal and 136 Warning, written against XML element names. Rule logic reads like "If SketchExistsIndicator = true and MeasurementStandardPublisherType is not provided." That's XML talk for: you included a sketch but didn't say which measurement standard you used.
3. The GSE models. Collateral Underwriter and Loan Collateral Advisor score from the data.

This is why the 728 UAD 3.6 compliance rules matter so much. The rules don't care how your PDF looks. They care whether the right elements exist with the right values.

Common XML problems and what they mean in plain English

Some rule messages say "For assistance with this message, contact the appraisal software vendor." Those are usually about how the file was written, not about your appraisal. Others are about what you entered. Here's how to tell them apart:

Tip: When a lender forwards a UCDP message with a rule ID like UAD1461, look the ID up in Appendix H-1. The row gives the message, the logic and the section. It turns a vague complaint into a specific field.

What good software does with the XML

You shouldn't have to think about elements and namespaces. Your software should:

• Write the XML from your entries, using the GSE schema's element order.
• Validate the XML against the GSE schema every time it builds the package.
• Render the PDF from the same data, so the two always match.
• Name and reference images correctly, and refuse to build if a referenced image is missing.
• Check the H-1 rules while you work and take you to the field when one fires.
• Produce the zip to B-1's folder structure.

Carat does each of those. It writes MISMO 3.6 XML validated against the GSE XSD on every build, renders the URAR PDF to the Appendix E style guide, and packages the UCDP-ready zip with the Images folder per Appendix B-1. Its AI-powered readiness checks evaluate hundreds of the H-1 rules locally while you type, each one linked to the field. It doesn't submit to UCDP or sign anything for you. You or your client upload the zip. See pricing.

Your old MISMO 2.6 files are still valuable

If you've been appraising for a while, you have years of MISMO 2.6 XML files sitting in your old software, or you can export them. Most desktop programs, including ACI and TOTAL, can export MISMO 2.6 GSE XML, and ClickFORMS files can be read directly. Those files are structured data about every subject and comp you've ever worked on.

That makes them a comps history and an adjustment record, not just a workfile obligation. Carat's legacy import takes a zip of thousands of them and turns them into a searchable history, with median adjustment rates by town and price tier drawn from your own reports. Anything unclear goes to a review queue instead of into a report. More on that in your past reports are a data set.

Where to go next

• For the full picture of the change, read the complete UAD 3.6 guide.
• To check that your package is right before your first live order, use the UAD 3.6 readiness checklist.
• To understand the rules that read your XML, see Fatal vs. Warning compliance rules.

If you'd like to see your own report as MISMO 3.6 XML, create an Carat account, build a practice report and open the zip.