The Apache Daffodil™ Extension for Visual Studio Code is an extension to the Microsoft® Visual Studio Code (VS Code) editor, designed for Data Format Description Language1 (DFDL) Schema developers.
DFDL is a data modeling language used to describe file formats. The DFDL language is a subset of eXtensible Markup Language (XML) Schema Definition (XSD). File formats are rich and complex - they require a modeling language to describe them. Developing DFDL Schemas can be challenging, requiring extensive iterative development and testing.
The purpose of the Apache Daffodil™ Extension for Visual Studio Code is to ease the burden on DFDL Schema developers by enabling rapid development of high-quality DFDL Schemas, with syntax highlighting, code completion, data file editing, and debugging of DFDL Schema parsing operations using Apache Daffodil™.
The Apache Daffodil™ Extension for Visual Studio Code provides syntax highlighting to enhance the readability and context of the text. It provides instant feedback to developers, indicating that the structure and code are syntactically correct.
The Apache Daffodil™ Extension for Visual Studio Code provides code completion, offering context-aware code segment predictions that can dramatically speed up DFDL Schema development by reducing keyboard input, developer memorization, and typos.
The Apache Daffodil™ Extension for Visual Studio provides a Daffodil parse debugger, enabling developers to control the execution of Daffodil parse operations. Given a DFDL Schema and a target data file, the developer can step through the execution of parse operations line by line, or until the parse reaches some developer-defined location, known as a breakpoint, in the DFDL Schema or the data being parsed. What is particularly helpful is that the developer can watch the parsed output, known as the “Infoset”, as it is being created by the parser, and watch where the parser is parsing in the data file. This enables the developer to quickly discover and correct DFDL Schema issues, making development and testing cycles more efficient.
The Apache Daffodil™ Extension for Visual Studio Code integrates with the Ωedit™ Data Editor extension for challenging Daffodil use cases. The data editor is declared as a VS Code extension dependency and is designed to support large files, of any type, that are well beyond the limits of the standard text editor in VS Code. It enables editing single or multiple bytes in various encodings, seeking to file offsets, searching and replacing byte sequences, profiling data, and determining a file's content type.
The Data Editor can be configured to open the designated data file when a Daffodil debug session starts. As the debug session steps to new byte positions, Daffodil sends byte-location highlights to the Ωedit™ Data Editor so the parse location is visible in the data content.
- Install VS Code, version 1.82.0 or greater
- Install Java Runtime 8 or greater
- On Linux, glibc 2.31 or greater is required
If additional help or guidance on using Apache Daffodil™, Apache Daffodil™ Extension for Visual Studio Code, or DFDL development in general is needed, please engage with the Daffodil user and developer communities on mailing lists (https://daffodil.apache.org/community/) and/or review the list archives (https://lists.apache.org/list.html?users@daffodil.apache.org).
Apache Daffodil™ and the Apache Daffodil™ Extension for Visual Studio Code are Apache Software Foundation (ASF) projects, are free open-source software, and are under active development. Feedback and contributions are welcome.
- Apache Daffodil™ Home Page (https://daffodil.apache.org)
- Apache Daffodil™ Extension for Visual Studio Code Repository (https://github.com/apache/daffodil-vscode)
- Apache Daffodil™ Extension for Visual Studio Code Wiki (https://github.com/apache/daffodil-vscode/wiki)
- Apache Daffodil™ Library Repository (https://github.com/apache/daffodil)
Apache Daffodil™ Extension for Visual Studio Code is licensed under the Apache License, v2.0.
This product includes the logback library, which is available under the Eclipse Public License v1.0.
This product includes the Java Debug Server for Visual Studio Code library, which is available under the Eclipse Public License v1.0.
This product includes the Xml Schema Object Model library, which is licensed under the Common Development and Distribution License Version 1.1.
This product includes the Regular Mono RedHatFont font, which is licensed under the SIL Open Font License, Version 1.1.
This product includes the space-grotesk font, which is licensed under the SIL Open Font License, Version 1.1.
Apache, the Apache logo, Apache Daffodil, Daffodil, and the Apache Daffodil logo are trademarks of The Apache Software Foundation. Visual Studio Code and VS Code are trademarks of Microsoft® Corporation. All rights reserved.
1 Data Format Description Language (DFDL) is a standard from the Open Grid Forum (www.ogf.org), available here (https://ogf.org/documents/GFD.240.pdf).
Copyright © 2025 The Apache Software Foundation. Licensed under the Apache License, Version 2.0.
Apache, Apache Daffodil, Daffodil, and the Apache Daffodil logo are trademarks of The Apache Software Foundation.