diagrams.net — Free Flowcharts and PRISMA Diagrams

What diagrams.net is

diagrams.net — still widely called draw.io, and still using that extension — is a free diagramming application for flowcharts, structured diagrams, and anything built from shapes connected by lines. It runs in a browser or as a desktop application, and files save wherever you tell them to: local disk, Google Drive, OneDrive, or a Git repository.

The design decision worth noticing is that connectors are attached to shapes rather than drawn between coordinates. Move a box and its arrows follow, re-routing around whatever is in the way. That sounds trivial and is the entire difference between a diagram you can revise and one you redraw — which is why a PRISMA diagram or a study-design flowchart is a twenty-minute job here and a frustrating afternoon in a general vector editor. It is genuinely free with no account, no watermark, and no premium tier, which is rare enough to state plainly.

Why researchers use it

A built-in PRISMA template — the systematic-review flow diagram, ready to fill in with your counts, rather than reconstructed from a published example.
Connectors that stay connected — restructure a methodology flowchart by dragging boxes and the arrows re-route themselves.
Free with no account — open the site and work. Nothing to sign up for, nothing watermarked, no feature held back.
SVG export — vector output that meets journal requirements and can be finished in Inkscape if it needs to match a house style.
Version-controllable — the VS Code extension edits .drawio files in place, so a methodology figure lives in the repository beside the analysis it describes.

Where it fits in a research workflow

diagrams.net owns the structured-figure slot: study designs, PRISMA flows, data pipelines, system architectures, conceptual frameworks, and ML model diagrams. Anything that is fundamentally boxes, arrows, and labels.

It divides the diagramming space cleanly with its neighbours. Mermaid is better when the diagram should be text and auto-laid-out — a flowchart in a README that must stay current. Excalidraw is better for fast sketching where a hand-drawn look is appropriate. Inkscape is better when you need precise typography, LaTeX equations, or a figure that matches a paper’s visual identity exactly — and the common pattern is to build structure here, export SVG, and finish there. What none of them do is plot data; that is matplotlib’s job.

Getting started

Twenty minutes.

Open diagrams.net and choose where files save — local disk keeps it simplest, and a repository folder is better still if the diagram documents code.
For a systematic review, search the template gallery for PRISMA and start there. Filling in a correct template beats reconstructing the structure from a published figure.
Learn one shortcut: hover a shape edge and drag to create a connected arrow and a new box in one gesture. It is most of the speed advantage.
The step people skip: export SVG rather than PNG, and keep the .drawio source file alongside it. The PNG is what goes in the slide deck; the source is what you edit when a reviewer asks for one more exclusion box.

diagrams.net vs the alternatives

Alternative	Does it better	Pick it if
Mermaid	Diagrams as text that live in a repo and auto-lay-out	The diagram documents code and must stay current
Excalidraw	Speed and a sketch aesthetic for thinking	You are working something out, not publishing it
Inkscape	Precise typography, LaTeX notation, house style	The figure goes into a journal and must match
Canva	Templates and visual polish for posters	The deliverable is a poster, not a diagram

diagrams.net is the best free tool for structured diagrams. It has no real weakness except that its default output looks like what it is: a competent, generic flowchart.

Cost, licensing, and your data

Free, with no paid tier for the core application — funded by a company selling Confluence and Jira integrations to enterprises rather than by monetising individual users. The desktop application and the core are open source.

Its data position is unusually good. There is no account requirement and no default cloud storage: files go where you point them, including entirely local disk. That means an unpublished study-design diagram or a figure containing sensitive detail never touches a third-party service unless you choose to save it to one. The desktop app makes this explicit and is the right choice for anything confidential.

The honest review

Strengths. It does the boring, essential job perfectly and charges nothing. For a systematic review, the PRISMA template alone saves an afternoon and prevents the small structural errors that reviewers notice. The connector model makes revision cheap, which matters because methodology diagrams are revised constantly — every protocol amendment and every reviewer comment touches the flowchart.

Limitations. Default output is visually generic — competent, neutral, and identifiable as a draw.io diagram, which is fine for a methods figure and wrong for anything meant to be visually distinctive. Typography control is basic and there is no LaTeX, so equations and specialised notation need finishing elsewhere. The interface is dated and the shape libraries are enormous enough to be hard to navigate. And exported SVGs carry more structural cruft than a hand-built vector file, which occasionally matters when someone downstream edits them.

Verdict. Adopt it for any structured diagram — it is free, it is fast, and there is no reason to use anything else for a flowchart. Skip it when the figure needs to be visually distinctive or typographically precise, where Inkscape takes over. The condition that flips the answer is whether the diagram is conveying structure or making an argument.

When NOT to use this Do not treat a PRISMA template as a substitute for correct numbers. The template gives you the right boxes; the counts inside them have to reconcile — records identified, duplicates removed, screened, excluded with reasons, included — and a reviewer who adds them up will find a diagram that does not balance. The template makes the figure look right, which is exactly why arithmetic errors survive in it. Check the totals against your actual screening records, not against the diagram.

Common questions

Is diagrams.net free?

Yes, entirely — no account, no watermark, no premium tier for the core application, and the desktop version is open source. It is funded by enterprise integrations rather than by charging individuals.

Does diagrams.net have a PRISMA template?

Yes, in the template gallery. Search PRISMA when creating a new diagram, then edit the counts and labels. It is the fastest correct route to the flow diagram a systematic review requires.

Can I version-control diagrams.net files?

Yes. .drawio files are XML, and the VS Code extension edits them in place, so a diagram can live in your Git repository beside the code or protocol it documents and be reviewed like any other file.