15 Licensing

Reference: Cheat sheet · CLI · Configuration · Cell options · Troubleshooting · Accessibility · Licensing

Taliesin is licensed under the GNU Affero General Public License v3.0. That governs the program, not the blog posts, lecture notes, papers and books you write with it. (What happens to your documents if the program stops being maintained is a different question, answered with numbers in Section 2.4.)

15.1 AGPL source in built pages

A built page is self-contained: it needs no CDN or other network fetch at view time, and no build step for the reader. Taliesin does this by copying its own stylesheets and scripts into the page it produces (base.css, tali-js.js, the code-enhance/ fragments, mermaid.js for a page with diagrams). A page you build therefore contains a copy of some of Taliesin’s own AGPL-licensed source. That raises the question of whether the page itself is an AGPL work, obliging you to offer its source to your readers.

15.2 The Output Exception

The Output Exception, LICENSE-OUTPUT-EXCEPTION.md at the repository root, answers that question. It is an additional permission under AGPL section 7, the same instrument GCC uses so that compiling a program with GCC does not make the program GPL.

Under the exception:

• Your document is yours. Building or serving it with Taliesin does not make it, its source, or its contents an AGPL work.
• Nothing to attribute. You do not have to reproduce the exception, the AGPL, a copyright line, or an offer of source anywhere in a page you build.
• Publishing is not a section 13 trigger. Hosting output that contains Taliesin’s runtime does not, by itself, oblige you to offer anyone source.
• It applies however you produced the output, build or preview alike.

You may publish, sell, host or relicense what you build, under any terms you choose.

15.3 What the AGPL still covers

The AGPL covers Taliesin itself. If you modify Taliesin and run the modified version as a network service, you owe its users the corresponding source. That obligation is why Taliesin uses the AGPL, and the exception leaves it intact. The runtime assets are AGPL as source in the repository; the exception applies only to the copies that land in a built document.

Vendored third-party assets (KaTeX, D3, Observable Plot, Mermaid) keep their own licences. Those licences are permissive and impose no copyleft obligation on your document. They are listed in THIRD_PARTY.md and crates/core/assets/js/LICENSES.md.