.XDD file extension
To open .XDD files on Windows, determine the source of the file: if it came from FairCom RTG utilities or COBOL-IT projects, treat it as an RTG/COBOL data dictionary; otherwise it may belong to another program (e.g., Xfit).
To open a .XDD file, start by trying a text/XML editor because FairCom RTG XDD files are XML. If the file was generated/used by FairCom RTG utilities or COBOL-IT tooling (e.g., Data Displayer), open it there to correctly interpret schemas, keys, and settings.
Last updated: October 13, 2026
Open on your device
Choose your operating system for a dedicated step-by-step opening guide.
How to open .XDD files
Use these platform-specific instructions to open .XDD files safely.
Windows
- Determine the source of the file: if it came from FairCom RTG utilities or COBOL-IT projects, treat it as an RTG/COBOL data dictionary; otherwise it may belong to another program (e.g., Xfit).
- If it is an RTG XDD file, open it in an XML-capable text editor to view the <schema> / <key> structure, or open/import it in the relevant FairCom RTG utility or COBOL-IT tooling that references “settings from an XDD file”.
- If it does not resemble XML, use the originating application/workflow (for example, Xfit if that is the known source).
Mac
- Try opening the .xdd in a plain text or XML editor to check whether it is XML (look for tags like <schema> and <key>).
- If it is an RTG/COBOL dictionary file, the most reliable use is on the system where FairCom RTG utilities or COBOL-IT tooling is installed; transfer the file to that environment to use it as intended.
Linux
- Open the file in a text editor to confirm it is XML and inspect for XDD schema elements such as <schema> and <key>.
- For workflow use (generation/consumption), use the FairCom RTG utilities that generate/operate on XDD files (e.g., xddgen) in the same environment as your RTG/COBOL build artifacts.
iOS
- If you only need to inspect the file, open it in a text/XML viewer app to see whether it is XML; for actual RTG/COBOL usage, move it to a desktop environment with the relevant tooling.
Android
- Open the file with a text/XML viewer to check if it contains XDD XML (<schema>, <key>); if you need to use it for RTG/COBOL tooling, transfer it to a desktop with the corresponding utilities installed.
Security notes
- FairCom RTG XDD files are XML; treat .xdd from untrusted sources as untrusted input for XML parsers and for any tooling that will use it to interpret/drive access to data files (a maliciously crafted schema could trigger edge cases in parsers).
- Because .xdd is an ambiguous extension used by more than one niche application, do not assume a file is safe or of a given type based only on the extension—confirm whether it is XML and whether it belongs to your expected workflow before importing it into specialized tools.
Can't open this file?
These are the most common causes and fixes when .XDD files fail to open.
Common reasons
- The .xdd file opens as unreadable characters (not XML)
- Your tool cannot interpret the data file correctly even with the .xdd present
- Windows shows 'Choose an app to open this file'
Fix steps
- Open the file in a text editor and check whether it starts with XML-like content and includes elements such as <schema> or <key> (typical of FairCom RTG XDD).
- If it is not XML, identify the source application/workflow (file-extensions.org notes Xfit usage) and open it with that application instead.
OS-specific troubleshooting
What is a .XDD file?
In the FairCom RTG ecosystem, an XDD file is an XML structure that defines record schemas and indexes (keys) associated with a data file. The schema uses elements such as <schema> and <key> to describe the layout and indexing metadata. Some .xdd files in the wild are not RTG-related (file-extensions.org notes usage by Xfit), so file origin matters.
Background
FairCom documents XDD as an XML schema structure used to define indexes and record schemas in a data file, including core elements like <schema> and <key>. This makes the file a “data dictionary” that other tools can use to interpret binary/record-oriented data correctly.
In practice, .xdd files are often produced as part of COBOL-oriented workflows. FairCom RTG utilities include tools such as xddgen, which can generate RTG XDD files from COBOL source, supporting environments that need consistent metadata for record definitions and indexing.
COBOL-IT tooling also uses .xdd as a configuration/dictionary artifact: documentation describes both generating XDD files via a compiler flag (-fgen-xdd) from COBOL FDs and using settings from an XDD file for use by tooling such as Data Displayer.
Because .xdd is not exclusive to one ecosystem, you may encounter .xdd files tied to other niche applications (for example, Xfit data). When a .xdd file does not look like XML, it is likely not an RTG XDD schema and should be opened with the application that created it.
Further reading
Authoritative resources for more details on the .XDD format.
- FairCom — RTG XDD schema structure (Appendix B)
- FairCom — RTG utilities overview (includes xddgen)
- COBOL-IT Developer Studio – Getting Started: The Basics (PDF) (mentions “Use settings from a XDD file” and -fgen-xdd)
- COBOL-IT Developer Studio – Getting Started: The Basics documentation (PDF)
- XDD file: How to open? (file-extensions.org) (notes alternate Xfit usage)
- IANA Media Types registry
Common .XDD issues
The .xdd file opens as unreadable characters (not XML)
Many .xdd files are RTG XDD schemas stored as XML, but the extension is also used by other niche software. If the content is not XML, it may not be a FairCom RTG XDD schema.
- Open the file in a text editor and check whether it starts with XML-like content and includes elements such as <schema> or <key> (typical of FairCom RTG XDD).
- If it is not XML, identify the source application/workflow (file-extensions.org notes Xfit usage) and open it with that application instead.
Your tool cannot interpret the data file correctly even with the .xdd present
In RTG/COBOL workflows, the XDD must match the actual record layout (COBOL FD definitions) and index definitions. A mismatched or outdated XDD can cause wrong field interpretation.
- Regenerate the XDD from the authoritative source definitions (e.g., COBOL FDs) using the appropriate generator workflow (COBOL-IT docs describe -fgen-xdd; FairCom RTG utilities list xddgen).
- Ensure you are using the XDD that belongs to the specific data file/version you are inspecting.
Windows shows 'Choose an app to open this file'
.xdd is not a widely registered consumer format and may not have a default association. Also, multiple unrelated programs can use the same extension.
- Open it with a text/XML editor first to determine whether it is an RTG XDD XML schema.
- If it is RTG/COBOL-related, install/use the FairCom RTG utilities or the COBOL-IT tool that expects an XDD file (e.g., Data Displayer workflow referenced in COBOL-IT docs).
FAQ
Is a .xdd file just XML?
In the FairCom RTG context, yes: FairCom documents XDD as an XML schema structure, with elements such as <schema> and <key>. However, .xdd can also be used by other programs, so not every .xdd file is XML.
How are .xdd files created in COBOL workflows?
FairCom RTG utilities include tooling such as xddgen that generates RTG XDD files from COBOL source. COBOL-IT documentation also describes generating .xdd via a compiler flag (-fgen-xdd) from COBOL FDs for use by tooling such as Data Displayer.
What is the .xdd used for in FairCom RTG?
It acts as a schema/dictionary describing record layouts and indexes for a data file, using XML elements (e.g., <schema> and <key>) that define the structure needed to interpret and index records.
Is there an official MIME type for .xdd?
No specific .xdd MIME type is indicated by the provided sources. The IANA media types registry is the authoritative place to check for registered media types, and .xdd is not presented here as a registered type.
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