OSI Approved the Curl License

Daniel Stenberg recounts curl’s licensing history and explains why the curl license is now officially OSI‑approved. curl began under GPL, moved to the Mozilla Public License in 1998, added an MIT option in 2001, and in 2002 adopted what was thought to be MIT but involved a slight, lingering edit to the license text. That modified text led SPDX to give it a distinct identifier, “curl,” because it was not identical to a standard MIT license. Over the years Stenberg sometimes called it MIT for convenience, but the difference meant it lacked explicit recognition by organizations like FSF and OSI.

On April 17, 2026 the Open Source Initiative formally approved the curl license, giving it official open‑source status. Stenberg notes he only recently realized the approval had occurred and includes the full verbatim license: a permissive permission paragraph allowing use, copy, modification and distribution for any purpose with or without fee provided the copyright and permission notice remain, a standard “as is” warranty disclaimer, and an explicit restriction that a copyright holder’s name may not be used in advertising without prior written authorization. He frames the OSI approval as a welcome confirmation of the license’s openness.