Online Tool Store
· 4 min read
How to Generate a Random SVG Blob Shape
Heshan Fernando
Co-founder & COO
You’re building a landing page and want one of those soft, organic background shapes behind a hero image — the kind that’s become a staple of modern web design, breaking up rigid rectangles with something that looks hand-drawn but isn’t. Drawing one by hand in a vector editor takes real time getting the curve smooth and asymmetric enough to look natural instead of like a lumpy circle, and most people doing this aren’t illustrators — they just need a usable shape, fast.
The shape itself isn’t complicated geometry, but getting it to look organic rather than mechanically regular is the part that’s genuinely fiddly to do by hand.
What makes a blob shape look organic
A convincing organic blob is built from a closed curve through a set of randomly-offset points around a center, connected smoothly rather than with straight lines or sharp corners. A Catmull-Rom spline is a common technique for this — it produces a smooth curve that passes through each control point without the jagged look of straight-line connections, and by randomizing the points’ distance from center, you get an irregular, natural-feeling shape instead of a perfect circle or a stiff-looking polygon.
The practical output people want is an SVG — a scalable, code-friendly format that drops straight into a website’s markup or a design file without the resolution limits of a raster image.
Why people get stuck here
- Hand-drawing a smooth curve takes practice. Getting a freeform vector path to look organic rather than lumpy or too regular is a real illustration skill, not something most developers or marketers have practiced.
- Wanting variation, not one fixed shape. A single blob gets reused everywhere once you have it; being able to regenerate a new random variation is often more useful than one static asset.
- Needing it as usable SVG, not a raster image. A PNG blob doesn’t scale cleanly or recolor easily with CSS the way an inline SVG path does.
- Design tool overhead for a small asset. Opening a full vector design app to make one background shape is a lot of setup for something this specific.
What a good SVG blob generator looks like
Genuinely smooth, organic curves
The spline technique matters — a good blob generator produces curves that read as natural, not just a randomized polygon with rounded corners.
Adjustable points and randomness
Being able to control how many control points define the shape, and how much randomness is applied, lets you dial in anything from a subtle wobble to a dramatically irregular shape.
Clean SVG output
The result should be usable SVG markup you can drop straight into a page or design file, not a locked-down image you have to re-trace.
Common mistakes to avoid
- Using too few control points, which can make the “organic” shape look more like a rounded polygon than a natural blob.
- Overusing extreme randomness, producing a shape so irregular it reads as a mistake rather than an intentional design choice.
- Exporting as a raster image when an SVG would scale better and allow CSS-based recoloring without regenerating the shape.
- Reusing the exact same blob shape across every section of a page, which undercuts the organic, non-repetitive feel that makes blobs effective in the first place.
How to do it with SVG Blob Generator
Online Tool Store’s SVG Blob Generator creates a random, smooth organic blob shape as SVG using a Catmull-Rom spline, entirely in your browser.
- Open the SVG Blob Generator tool.
- Adjust the number of points and randomness to control how irregular the shape looks.
- Regenerate until you land on a shape you like.
- Copy the SVG output and drop it into your page, design file, or app.
Frequently asked questions
What’s a Catmull-Rom spline, and why does it matter here?
It’s a curve-fitting technique that produces a smooth path through a set of points without the sharp angles you’d get connecting them with straight lines — it’s what gives the generated blob its organic, hand-drawn-looking curve instead of a jagged or overly geometric outline.
Can I recolor or resize the blob after generating it?
Yes — since the output is SVG, you can restyle its fill color with CSS and resize it without any quality loss, unlike a raster (PNG/JPG) version of the same shape.
Why does the shape look different every time I generate one?
The generator randomizes each control point’s distance from the shape’s center within the range you set, so regenerating produces a new, distinct shape each time rather than a fixed template — useful when you want several unique variations for different sections of a design.
Final thought
For an organic background shape, generating an SVG with adjustable randomness beats hand-tracing a curve in a vector editor — you get several usable variations in the time it’d take to smooth out one hand-drawn attempt.