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Freeform Drawing in the Browser: Real Brushes, Pressure & Symmetry
This isn't a rectangle-and-arrow diagram tool with one flat pen bolted on. It's a genuine sketching surface, in the same tab as your diagrams.
Most diagramming tools bolt on a single flat "pen" as an afterthought — one width, one texture, good for a quick scribble and nothing else. FlowDiagrams takes a different position: freeform drawing is a first-class surface, modelled closely on how a real tablet drawing app behaves, sitting in the exact same canvas as your boxes and connectors.
Here's what that actually means in practice — every claim below is something you can try in the next two minutes, free, with no account.
Nine brushes that genuinely behave differently
These aren't nine icons pointing at the same underlying stroke. Each has its own physical model:
| Brush | What makes it distinct |
|---|---|
| Pen | Clean tapered line, the default all-rounder. |
| Pencil | Visible grain and fibre texture — reads like actual graphite, not a vector line. |
| Crayon | Heavier, waxier texture with a wider, softer edge. |
| Charcoal | Broad, soft-edged, deliberately imprecise — built for gesture, not detail. |
| Paint brush | The most fluid taper of the set, thin tail into a fuller body. |
| Marker | Flat-capped, no taper — consistent width start to finish, like a real marker nib. |
| Highlighter | Wide, translucent, and set to Multiply blend by default — it darkens through what's beneath rather than covering it, exactly like a real highlighter over printed text. |
| Airbrush | A genuine spray pattern, soft-edged and semi-transparent. |
| Watercolour | The softest, most translucent brush, also on Multiply — washes of colour build up where strokes overlap instead of flattening to one solid tone. |
Switch between them from the paint palette (the pencil icon in the top toolbar, or press W), or tap the brush you're already holding to open its full settings.
Real pressure sensitivity — not a gimmick toggle
If you're on an iPad with Apple Pencil, or a Windows machine with a pen display, FlowDiagrams reads actual hardware pressure data from the stylus and varies stroke width in real time as you press harder or lighter — the same signal a native drawing app uses. Press down at the start of a stroke and lift off gradually, and the tapered brushes (Pen, Pencil, Brush, Airbrush) narrow accordingly.
No stylus in hand? Drawing speed stands in for pressure automatically — slow down and the line widens, speed up and it thins — so strokes still taper convincingly with just a finger or a mouse.
Symmetry: mirror and radial drawing guides
This is the feature that tends to get an actual reaction. Turn on symmetry (the symmetry icon in the paint tray) and every stroke you draw is mirrored live as you draw it:
- Vertical / Horizontal — one mirror axis, instant left-right or top-bottom symmetry.
- Quadrant — mirrored across both axes at once, four-way symmetry.
- Radial — draw once, repeat automatically around a centre point, with an adjustable sector count from 2 to 16. At higher sector counts this is a genuine mandala generator — draw one petal shape and watch fifteen more appear around it as you draw.
Each mirrored stroke is a real, independent stroke afterward — not a visual trick — so you can select and adjust any one of them individually once you're done.
Blend modes and smudging
Six blend modes are available on any stroke — Normal, Multiply, Screen, Overlay, Darken, Lighten — the same set a raster image editor offers, applied live as you paint rather than as a filter afterward. Layer a Multiply stroke over a Screen stroke and they interact the way light or ink actually would.
The smudge tool drags existing painted colour around the canvas — genuinely pushing pixels, not just adding a new stroke on top — useful for blending edges or softening a transition between colours.
Save a brush exactly as you set it up
Once you've dialled in a brush — a specific size, opacity, smoothing and colour combination — Save current brush keeps that exact configuration as a one-tap preset, so you're not rebuilding "the same slightly-transparent grey marker" from scratch every session.
Five canvas surfaces to draw on
Beyond a blank white canvas, ☰ → Canvas surface… gives you Paper, Canvas, Dots, or Ruled textures underneath your drawing. It's part of the document itself, so it exports along with everything you've drawn — a dotted-grid background for a quick UX sketch, or ruled lines for handwritten notes alongside a diagram.
Why this lives inside a diagram tool at all
The practical reason: the fastest way to annotate a diagram is often to just draw on it — circle the problematic system, sketch an arrow at an angle no connector tool handles gracefully, cross something out. Keeping real drawing tools in the same canvas as the shapes means you never have to export to an image editor and reimport just to add a handwritten note.
Frequently asked questions
- Does it actually support pressure sensitivity, or is that simulated?
- Both, depending on your input. With a real stylus — Apple Pencil on iPad Safari/Chrome, most Windows pen displays — it reads genuine hardware pressure and varies the stroke width as you press harder or lighter. With a finger or mouse, there's no pressure signal to read, so it simulates the same tapering effect using drawing speed instead: slow down and the line widens, the way a real brush behaves.
- Can I mix freeform drawing with the diagram shapes?
- Yes. Painted strokes and diagram shapes share the same canvas and the same layer system — nothing separates "drawing mode" from "diagram mode" into different documents. Circle a problem area by hand, sketch an arrow pointing at a box, or annotate a screenshot you've pasted in, all without leaving the diagram.
- Is a mouse good enough, or do I need a tablet and stylus?
- A mouse or trackpad works for everything — every brush, symmetry mode, and blend mode. A stylus adds genuine pressure control, which is most noticeable on expressive brushes like the paint brush or watercolour. It's a meaningful upgrade, not a requirement.
Try it yourself
FlowDiagrams is free, works offline, and never uploads your diagram anywhere.
Open FlowDiagrams →