The battle for document format supremacy has entered a new, more contentious phase, with LibreOffice launching a public offensive against fellow open-source office suite vendor ONLYOFFICE, accusing it of being "fake open-source" and aligning too closely with Microsoft's proprietary interests. This conflict, which erupted publicly in late 2024, goes far beyond typical software rivalry—it strikes at the heart of digital sovereignty, vendor lock-in, and the very definition of open standards in an era where document formats dictate interoperability and long-term data accessibility. The debate centers on two competing XML-based formats: the OpenDocument Format (ODF), championed by LibreOffice and the open-source community, and Microsoft's Office Open XML (OOXML), which ONLYOFFICE has embraced with increasing fidelity.

The Core Conflict: Open Standards or Strategic Alignment?

At its essence, this dispute is about philosophy and control. LibreOffice, developed by The Document Foundation, is built on a staunch commitment to ODF (specifically ODF 1.2 and 1.3). ODF is an ISO/IEC standard (26300) developed independently of any single vendor, originally by the OASIS consortium. Its proponents argue it represents a true, vendor-neutral open standard designed to ensure documents remain accessible regardless of the software used to create them. Conversely, Office Open XML (OOXML), standardized as ISO/IEC 29500, was developed by Microsoft and, while also an ISO standard, is intrinsically linked to the feature set and design principles of Microsoft Office. ONLYOFFICE's strategy has been to prioritize flawless compatibility with Microsoft's formats, positioning itself as the best open-source alternative for environments deeply entrenched in the Microsoft ecosystem.

LibreOffice's criticism hinges on the belief that by prioritizing OOXML compatibility, ONLYOFFICE is effectively reinforcing Microsoft's de facto standard and the associated vendor lock-in, rather than championing a truly open alternative. They argue this makes ONLYOFFICE's open-source claims disingenuous—"fake open-source"—because its development priorities serve to perpetuate a proprietary ecosystem. A search for recent statements from The Document Foundation confirms this stance, with community members expressing concern that such close alignment undermines the broader fight for open standards.

Technical Divergence: ODF Fidelity vs. OOXML Compatibility

The technical divide between the suites is significant. LibreOffice uses ODF as its native, default format. Its handling of OOXML (.docx, .xlsx, .pptx) is achieved through import/export filters, which can sometimes lead to formatting discrepancies with complex documents. This is a conscious trade-off: fidelity to the open standard is paramount. ONLYOFFICE, however, treats OOXML as a first-class citizen. Its editors are designed to parse and save OOXML files with high accuracy, minimizing the "round-trip" problem where a document edited in a different suite loses formatting when reopened in Microsoft Office. This technical approach is a direct response to market demand, especially from businesses and governments that must exchange documents with partners using Microsoft Office.

Searching for comparative analyses reveals that this technical choice has real-world implications. For pure ODF workflows, LibreOffice often provides a more robust experience. For environments where seamless exchange of .docx files is non-negotiable, ONLYOFFICE frequently receives higher marks for compatibility. This isn't merely about fonts and margins; it extends to advanced features like complex spreadsheet formulas, embedded objects, and tracking changes, where OOXML's specification is deeply intertwined with Microsoft Office's behavior.

The "Fake Open-Source" Allegation and Community Governance

LibreOffice's "fake open-source" barb is particularly pointed in the context of software freedom and community-led development. The Document Foundation operates under a clear, contributor-friendly governance model (using the MPLv2.0 license) and its roadmap is heavily influenced by its global community of volunteers and developers. ONLYOFFICE, while its core code is available under the GNU AGPLv3.0 license, is developed primarily by Ascensio System SIA, a for-profit company. Critics argue this leads to a development process that is more corporate-driven, with priorities set to meet commercial demands—like superior Microsoft compatibility—rather than purely ideological goals of open standards advocacy.

Investigating the repositories and community forums for both projects supports this distinction. The LibreOffice project showcases a vast, decentralized network of contributors, while ONLYOFFICE development appears more centralized. However, branding this as "fake" is controversial. By the strict definitions of the Open Source Initiative (OSI), ONLYOFFICE is unequivocally open-source software. The conflict, therefore, is less about licensing and more about ethos and strategic direction: is the goal to replace the proprietary standard, or to coexist with it as seamlessly as possible?

Market Realities and the User's Dilemma

For IT administrators, government agencies, and everyday users, this debate translates into a practical dilemma. The choice between LibreOffice and ONLYOFFICE is no longer just about features or price (both are free); it's about choosing a side in a format war. A government mandate favoring ODF for long-term archiving would naturally lean toward LibreOffice. A private company whose entire supply chain uses Microsoft 365 might find ONLYOFFICE's strategy more pragmatic, reducing friction and training costs.

Recent search trends show growing interest in both suites, particularly in the EU and other regions where digital sovereignty and reducing dependence on large US tech firms are political priorities. The European Interoperability Framework recommends open standards like ODF, giving LibreOffice a policy advantage. However, the inertia of the Microsoft Office ecosystem is immense, giving weight to ONLYOFFICE's compatibility-first argument.

The Microsoft Factor and the Future of Interoperability

Microsoft's role in this is complex. The company has been a member of OASIS and supports ODF saving in Microsoft Office, but its implementation has historically been criticized as lacking full fidelity. The partnership aspect hinted at in the conflict—where ONLYOFFICE is seen as aligning with Microsoft—could refer to technical collaboration or simply to building a product that complements rather than directly challenges the Microsoft ecosystem. Some analysts suggest that a robust, open-source editor with excellent OOXML support indirectly benefits Microsoft by validating the format's longevity and reducing pressure to improve its own ODF support.

The future may hinge on the evolution of the standards themselves and the rise of collaborative, web-based editing. ODF 1.3 introduced important new features, and work continues. OOXML is also updated with each new Microsoft Office release. The advent of universal standards like WebAssembly and web-centric APIs could eventually reduce the importance of native file formats, but that future is still distant. For now, the format a document is saved in remains a critical decision impacting its utility and accessibility for decades.

Conclusion: A Necessary Debate for Digital Independence

The heated exchange between LibreOffice and ONLYOFFICE, while acrimonious, highlights a crucial and ongoing battle for the digital infrastructure of our society. It is a debate between purity of principle and pragmatism of adoption. LibreOffice stands as the unwavering flag-bearer for vendor-neutral, ISO-standardized open formats, viewing compromise as a slippery slope back to proprietary control. ONLYOFFICE represents a pragmatic path to open-source adoption within the reality of a Microsoft-dominated world, arguing that perfect interoperability is the key to user freedom.

For users and organizations, the choice demands careful consideration of their values, workflows, and long-term digital preservation needs. There is no single right answer, but the increased scrutiny and debate ultimately serve the public interest by pushing all players—including Microsoft—toward greater transparency, better interoperability, and a stronger commitment to the open standards that ensure our digital documents remain free from lock-in and accessible to future generations. The war of words may be fierce, but it underscores that the fight for control over our most basic digital artifacts—our words, data, and presentations—is more relevant than ever.