Free PlantUML for Confluence: what "free" actually gets you

Search the Atlassian Marketplace for PlantUML and you'll find both free and paid apps for Confluence Cloud. If the free ones render the same diagrams, the obvious question is what the paid ones are for — and the slightly sharper question is what "free" is going to mean in three years. The category's own history says that's worth asking before you standardize a wiki on any of them.

Free is a moving target in this category

Two documented facts frame the decision:

• Free apps can become paid apps. The most widely adopted PlantUML app in the category started out free and later moved to a paid model — the vendor maintains its own page explaining the free-to-paid transition. Nothing improper about that; it's simply what happens when an app has ongoing server costs and a team behind it. But it means "free" on the listing describes today, not necessarily your renewal.
• Free apps can stall. In March 2025, users of a different free PlantUML app reported every macro failing with an app-version error and no update available to install; the thread was never resolved. A free app with no revenue has no obligation to keep up with platform changes — sometimes it just doesn't.

Neither fact is an argument against free apps. Both are arguments for knowing why a given app is free before you adopt it.

The checklist: which kind of free is this?

Before standardizing on any free PlantUML app, check four things on its listing and docs:

1. Is it maintained? The listing shows a last-updated date. An app that hasn't shipped in a long time carries platform-deprecation risk you'll discover at the worst moment.
2. Where does your diagram source live? If it's stored in the macro body inside your pages, you keep your diagrams no matter what happens to the app. If it's stored on the vendor's side, the app's fate is your data's fate.
3. Can you see what it does? Open source means the data path — what leaves the page, where it goes — is checkable rather than promised. Closed and free means trusting a privacy policy with no revenue behind it.
4. What does free cost to operate? An app that runs vendor servers has real per-user costs someone eventually pays — through a paid tier, an acquisition, or abandonment. An app with no server side has no such pressure.

Why this one is free

Palori's PlantUML for Confluence is free, and the reason is architectural rather than promotional: there is nothing to pay for. The app has no backend — it renders client-side by composing a request to a PlantUML server (the public one, or yours), stores your diagram source in your own pages, and keeps exactly one piece of configuration (your render-server URL) in Forge's storage. No servers to run means no per-user cost to recover, which is what makes free sustainable rather than introductory.

And because the app is source-available — the code is public at github.com/paloriapps/plantuml-confluence — each claim in that paragraph is checkable against the source rather than taken on faith. That's the practical difference between "free and source-available" and just "free": you can verify what you're adopting, and the parts that matter (your diagram text, the open-source PlantUML server) stay yours either way.

The honest caveat

Free-and-source-available is not free-of-responsibility. If you use the public render server, your diagram source travels to it — fine for most diagrams, wrong for some (the self-hosting guide covers taking that in-house, which does cost you a container to run). And paid apps aren't a mistake: a paid vendor owes you support and has revenue to fund platform upkeep — for some teams that guarantee is exactly what they're buying. What you shouldn't do is pick a free app because the price column says free, without knowing which kind of free it is.