What is the RML file format?
An .rml file is an XML-based annotation overlay used with Autodesk's CAD viewing applications. RML stands for Redline Markup Language - a proprietary Autodesk XML schema designed to let engineers and reviewers attach comments, highlights, and geometric markups to a base .dwg or .dwf drawing without altering the source file.
The .rml file contains no drawing geometry of its own. It references its base CAD document via a BaseDocument element and organises annotation shapes - boxes, circles, polylines, arcs, text notes, revision clouds - into MarkupPlanes layers, allowing multiple reviewers to maintain separate annotation sets over the same drawing.
The format was introduced with Autodesk Volo View and AutoCAD 2000i around 2000. AutoCAD accepted .rml imports via the RMLIN command-line tool through AutoCAD 2005; later releases dropped that support. Volo View was discontinued on 1 May 2005 and replaced, eventually, by Autodesk Design Review - itself now also discontinued.
Today .rml is a legacy format with no active authoring tool. Files are readable as plain XML in any text editor, but without the original base drawing the annotation data has no useful context. Modern Autodesk annotation workflows use DWF-based markup instead.
Security & safety
RISK: LOWAn .rml file is a plain XML text file containing annotation data. It cannot execute code. As with any XML file, malformed or adversarial XML could theoretically exploit a vulnerable XML parser, but the practical risk is negligible.
Format details
in a nutshell- Report Markup Language (RML) - RML is also used by some reporting tools (e.g., Reportlab's RML) as an XML-based page layout language for generating PDFs - unrelated to Autodesk.
- RmlUi Markup Language - HTML/CSS-subset XML used by the RmlUi library for game UI - unrelated to Autodesk.
Programs that open RML files
Windows3 apps
Windows Notepad
Built-in Opens .rml as plain text; useful to read annotation text content but no visual rendering. 
Notepad++ (text editor - XML view)
Open-source Open the .rml file to inspect raw XML annotation data. Renders readable XML structure but not the visual markup.
AutoCAD (up to 2005 only via RMLIN)
Paid AutoCAD 2005 and earlier: use the RMLIN command to import the .rml as a locked '_Markup_' layer. AutoCAD 2006 and later: RMLIN was removed - not supported. Technical details
deep spec| File type | XML-based CAD annotation overlay (redline markup) |
| Encoding | Text, XML (UTF-8 or as declared in XML declaration) |
| Container | Plain XML document |
| Annotation shape types | Box, Circle, Spline, Polyline, Arc, Ellipse, Text, Note, Cloud, Callout, Group |
| Drawing geometry | None - annotation overlay only; base drawing referenced via BaseDocument element |
| Base file types | .dwg and .dwf (Autodesk drawing formats) |
| Typical size | 1 KB - 500 KB (annotation data only) |
| AutoCAD import command | RMLIN (supported through AutoCAD 2005 only; removed in later versions) |
| XML schema reference | Autodesk Redline XML schema, documented in patents US6675355B1 and US6964015B2 |
| Authoring application | Autodesk Volo View (discontinued 1 May 2005) |
| Successor format | DWF-based markup via Autodesk Design Review (also discontinued) |
| Markup layers | MarkupPlanes element groups annotations into named reviewer layers |
| Associated OS | Windows only |
| Status | Obsolete; no active authoring tool available since 2005 |
| Released | circa 2000 (Autodesk Volo View / AutoCAD 2000i era) |
| Latest version | N/A - format frozen; Volo View discontinued 2005, AutoCAD dropped RML import after AutoCAD 2005 |
| Specification | patents.google.com |
Community Q&A
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