OSI Adopts SPDX IDs for License URLs
For more than 25 years, the Open Source Initiative (OSI) website has been a central reference point for Open Source licenses. Over that time, our site has evolved through multiple redesigns, content management systems, and infrastructure migrations. As a result, license pages accumulated a variety of URL formats, including some ending in html, php, and txt.
In 2025 alone, our most-referenced license pages received significant traffic:
- MIT: over 1.5M pageviews
- Apache 2.0: 344K pageviews
- BSD 3-Clause: 214K pageviews
With this level of usage, even small inconsistencies in URLs, naming, or structure can have outsized effects across the ecosystem. Ensuring that license identifiers are clear, stable, and aligned with widely adopted standards is essential.
That’s why we’ve taken this step to standardize OSI license URLs using SPDX identifiers, while carefully preserving compatibility with the many links that already exist across the web and tools. The full set of OSI-approved licenses continues to be available at:
https://opensource.org/licenses
Why SPDX?
SPDX (Software Package Data Exchange) license identifiers have become the de facto standard for referencing software licenses in a consistent, machine-readable way. They are widely used across the Open Source ecosystem: in package managers, compliance tools, SBOMs, and documentation.
By adopting SPDX IDs in our URLs, we are aligning OSI’s license pages with the identifiers that developers, organizations, and tools already rely on.
Preserving the Past with Redirects
We recognize that OSI license URLs are deeply embedded across the web: in documentation, legal texts, source code comments, blog posts, and academic papers. Breaking those links would create unnecessary friction.
That’s why all legacy license URLs continue to work. We’ve put appropriate redirects in place so that older links now resolve cleanly to the corresponding SPDX-based URL.
In short: nothing breaks, and everything becomes clearer going forward.
Summary of License URL Changes
To support the transition to SPDX-based identifiers while preserving long-standing links, we standardized license URLs and implemented redirects from legacy formats. The table below summarizes the types of changes applied across the OSI website.
Improved Consistency and Clarity
Using SPDX identifiers brings several benefits:
- Consistency: One canonical identifier per license, across OSI’s site and beyond.
- Clarity: License URL matches what developers see in tooling and manifests.
- Interoperability: Easier integration with compliance, scanning, and automation tools.
- Future-proofing: A stable foundation for continued improvements.
Please note that, while SPDX license identifiers include dots (for example, Apache-2.0), our website URLs use a hyphenated form for compatibility with our current publishing platform. Requests using the dotted SPDX form will continue to work and are automatically redirected, while the SPDX identifier itself is preserved in metadata and API responses.
License Data Available via the OSI API
In addition to updating our website URLs, OSI license data is available through our API, making it easier for developers and organizations to consume authoritative license information directly from OSI.
This supports automation, integrations, and new use cases that depend on accurate, up-to-date license metadata, without scraping or manual maintenance.
Looking Ahead
This update is part of our ongoing effort to modernize OSI’s infrastructure while respecting the history and stability that the Open Source community depends on. Standardizing license URLs using SPDX identifiers helps ensure that OSI remains a reliable, relevant, and interoperable reference point for Open Source licensing in the years ahead.
As always, we welcome feedback from the community. If you spot an issue or have suggestions for further improvements, please let us know.