Serendipity (s9y) is a free, open-source PHP blogging and CMS platform. See 2026 features, plugin architecture, pros and cons, and how it compares to WordPress.
Serendipity, known by the shorthand s9y, is a free, open-source PHP weblog engine that traces its roots back to a project called jBlog, started by Jannis Hermanns in the winter of 2002.
Unlike commercial SEO or SaaS tools, Serendipity is a community-maintained open-source project distributed under the permissive BSD 3-Clause license, meaning anyone can download, modify, and redistribute it, including for commercial use, without paying license fees.
The project is designed to serve both casual bloggers who want a simple out-of-the-box setup and developers who need an extensible framework for larger, multi-author publishing sites, all self-hosted on the user's own server.
Serendipity's plugin architecture is its defining feature, allowing users to extend both the appearance and functionality of a blog through templates and plugins that are managed and updated via the built-in SPARTACUS updater.
The software supports multiple database backends including MySQL, PostgreSQL, and SQLite, and includes a granular multi-user permission system so that larger sites can have several authors and administrators with different levels of access.
Beyond blog posts, Serendipity supports static pages, categories and tags, comment moderation with spam protection, and standards-compliant RSS and Atom feed generation, functioning as a lightweight general-purpose CMS.
Serendipity is completely free to download, install, and use, with no paid tiers, subscriptions, or licensing fees of any kind, since it is released under the open-source BSD 3-Clause license.
The only costs associated with running Serendipity are self-hosting expenses, such as web hosting, a domain name, and any premium third-party plugins or templates a user chooses to purchase from outside developers.
Because there is no vendor selling the software itself, support is provided through community documentation, forums, and the project's GitHub repository rather than a paid customer support channel.
Serendipity, or s9y, is a free, open-source PHP-based weblog engine and lightweight CMS that has been in development since 2002.
Yes, Serendipity is completely free and open source, released under the BSD 3-Clause license.
Serendipity uses the permissive BSD 3-Clause license, which allows free commercial and non-commercial use, modification, and redistribution.
Serendipity supports MySQL, PostgreSQL, and SQLite database backends.
Plugins and templates can be installed and updated through the built-in SPARTACUS updater, which connects to a central repository.
Yes, Serendipity is actively maintained by a community of developers on GitHub, with a current focus on modernization and backward-compatible security improvements.
Serendipity is a smaller, lighter-weight alternative to WordPress with a smaller plugin ecosystem but a similar self-hosted, plugin-driven architecture.
Yes, Serendipity supports multi-user and multi-blog configurations on a single installation.