I have written the declaration display: flex more times than I can count, and I still occasionally forget whether it is justify-content or align-items that controls the vertical axis in a row. That is not ignorance; it is the honest reality of a layout model whose behaviour flips depending on flex-direction. When the direction is row, justify-content works horizontally. Switch to column and the same property now works vertically. Anyone who claims they never open the browser dev tools to nudge these values until the boxes land where they want is either lying or has a much better memory than mine.
The Flexbox Generator is the tool I wish I had when I was learning this model, and the one I still reach for when I want to prototype a layout without touching a stylesheet. You set the container properties, a row of sample boxes reflows in real time, and the exact CSS that produces what you see sits in a copy-ready box underneath. It turns "remember which property does what" into "click until it looks right, then read off the answer."
TL;DR: Flexbox is a one-dimensional layout model. The container drives it through six properties:
flex-direction,flex-wrap,justify-content,align-items,align-content, andgap. This generator exposes all of them, shows a live preview, and emits clean CSS. Because the preview renders with the same declarations it outputs, what you see is exactly what you paste. It runs entirely in your browser with no signup.
What problem does a flexbox generator solve?
Flexbox is powerful precisely because it is relative. You describe intent ("spread these items with equal space between them," "centre this on both axes") and the browser computes the pixels. But relative systems are hard to hold in your head, because the effect of each property depends on the state of the others. align-content does nothing until items wrap. The main axis and cross axis swap when you change direction. space-between and space-around look similar until you compare them side by side.
The fastest way to build intuition for a relative system is to manipulate it and watch. A generator collapses the edit-save-refresh loop into a single interaction: change a dropdown, see the boxes move. After ten minutes with a live preview, the property that controls the cross axis stops being a fact you memorise and becomes something you feel. And when you are done exploring, you are not left with a mental note to transcribe; the working CSS is already written for you.
Which properties does the container control?
Flexbox splits responsibility between the container and its items. The container decides the overall arrangement, and that is where the generator focuses because it is where most layout decisions live. Here is what each container property does.
| Property | What it controls | Common values |
|---|---|---|
flex-direction |
The main axis and its direction | row, column, row-reverse, column-reverse |
flex-wrap |
Whether items overflow onto new lines | nowrap, wrap, wrap-reverse |
justify-content |
Spacing along the main axis | flex-start, center, space-between, space-evenly |
align-items |
Positioning on the cross axis | stretch, center, flex-start, baseline |
align-content |
Spacing of wrapped lines on the cross axis | stretch, center, space-between |
gap |
Space between items | any length, for example 16px |
The mental model that makes this stick is the two-axis idea from the specification. Items flow along the main axis, which flex-direction sets. The cross axis is always perpendicular to it. justify-content distributes space on the main axis; align-items positions on the cross axis. Once flex-direction is column, the main axis is vertical, so justify-content now stacks items top to bottom and align-items positions them left to right. Nothing about the properties changed; the axes rotated underneath them.
How do I centre a div with flexbox?
This is the single most searched flexbox question, and the answer is three lines. Set the container to display: flex, then justify-content: center and align-items: center. That centres the child on the main axis and the cross axis at once, which for a default row means dead centre horizontally and vertically.
In the generator, you pick center for both alignment controls and the sample boxes jump to the middle of the preview area. The output box then shows:
.container {
display: flex;
flex-direction: row;
flex-wrap: nowrap;
justify-content: center;
align-items: center;
}
The reason this recipe is worth building by clicking rather than memorising is that the moment your requirement changes even slightly, for example you want the item pinned to the top but centred horizontally, you change one dropdown and see the result, instead of guessing which of the two properties to edit.
When does align-content matter?
align-content is the property people set and then wonder why nothing happens. The answer is in the specification: it only affects layout when there are multiple lines of flex items. With flex-wrap: nowrap, every item sits on a single line, so there is no set of lines to distribute, and the property is inert.
The generator encodes this rule so you cannot be misled by it. When wrap is off, the align-content control is disabled and the property is omitted from the generated CSS entirely. Turn wrapping on and it becomes active, and you can watch it push the rows of wrapped items together or spread them apart on the cross axis. Emitting the property only when it does something keeps the output honest: every declaration in the copied rule is one that has a visible effect on your layout.
What is the difference between justify-content values?
The justify-content keywords are where a live preview earns its keep, because the differences are spatial and hard to describe in prose. flex-start packs items at the start of the main axis. center packs them in the middle. space-between pushes the first and last items to the edges and distributes the remaining space equally between the others, so there is no space at the outer edges. space-around gives each item an equal amount of space on both sides, which means the gap between two items is double the gap at the edges. space-evenly makes every gap equal, including the edges.
Reading that paragraph teaches you almost nothing. Clicking through the five values with five boxes on screen teaches you in seconds, and you will never confuse space-between with space-around again once you have seen the edge behaviour side by side. That is the argument for building layout by manipulation rather than by memorisation, and it is the same argument behind keeping a set of visual CSS tools close: the gradient generator and the box-shadow generator exist for the same reason, because gradients and shadows are also easier to dial in by eye than to write blind. The broader case for assembling that kind of toolkit is in this piece on the web developer toolkit.
Flexbox or CSS Grid?
This question comes up constantly, and the framing that it is a competition is the mistake. Flexbox is one-dimensional: it lays items along a single axis, wrapping when told to, and it excels at rows of things whose size you want the browser to negotiate. Toolbars, navigation bars, button groups, and card rows are natural flexbox jobs. CSS Grid is two-dimensional: it controls rows and columns together, and it excels at page-level structure where you want explicit tracks.
In real projects they nest constantly. A grid defines the page regions, and a flex container arranges the items inside one of those regions. Learning flexbox thoroughly does not make grid redundant and vice versa; it makes you fluent in the tool that fits each job. A generator is a fast way to reach that fluency for the one-dimensional case, and once the container properties are second nature, reading and writing flex layouts by hand stops needing a reference.
How do I use the Flexbox Generator?
The flow mirrors how you think about a layout.
- Choose
flex-directionand whether items should wrap. This sets the axes and the overflow behaviour, the two decisions everything else depends on. - Set alignment. Adjust
justify-contenton the main axis andalign-itemson the cross axis until the preview matches the arrangement in your head. - Tune spacing. Set the
gapbetween items with the slider, and when wrapping is on, setalign-contentto space the lines. - Copy the CSS. The generated rule targets a
.containerclass and updates live. Copy it in one click and paste it into your stylesheet.
You can also add or remove preview items to test how a layout behaves under different content. A space-between navbar looks fine with three items and very different with seven that wrap, and being able to change the count while watching is how you catch that before it reaches production.
Does gap replace margins for spacing?
Mostly, yes, and it is a real improvement. Before gap was supported in flex containers, spacing items meant adding margins to each child and then fighting the extra margin on the first or last one, usually with a :last-child override or a negative margin on the parent. gap sets the space between items directly, applies between wrapped lines as well, and adds nothing on the outer edges, so the whole class of edge-margin bugs disappears.
The generator treats gap as a first-class control with a pixel slider, and it omits the declaration when the gap is zero so the output stays minimal. For production work, gap on flex containers is well supported across current browsers, so there is rarely a reason to reach back for the margin approach. If you are converting a spacing value between units while you work, the CSS unit converter handles the px to rem arithmetic without a calculator.
What are the limits of the generated CSS?
The generator produces the container rule. It does not set per-item properties like flex-grow, flex-shrink, or flex-basis, which control how individual items expand and contract to fill space. Those are item-level decisions that depend on your specific content, and for most layouts the container properties plus flex: 1 on the items that should grow is all you need. When you do need fine per-item control, the generated container rule is still the correct foundation to build on.
The output uses standard, unprefixed properties. Vendor prefixes for flexbox were needed for browsers that are years out of support, so a modern stylesheet should not carry them, and adding them today is noise. The generated CSS is production-ready as written, which is the point: you leave with a rule you can paste, not a starting sketch you have to finish. For the wider set of small utilities that make front-end work faster, this rundown of developer productivity tools is a good companion, as is the gradient generator guide if visual CSS is the part you want to speed up.
Which common layouts can I build with it?
A handful of recipes cover most day-to-day flexbox work, and each is a few clicks in the generator. A navigation bar with a logo on the left and links on the right is justify-content: space-between with align-items: center on a row. A perfectly centred hero, the classic "centre a box on the page," is justify-content: center and align-items: center. A vertical stack of form fields is flex-direction: column with a gap for consistent spacing, which is cleaner than margins on every field. A responsive row of cards that wraps to new lines on narrow screens is a row with flex-wrap: wrap and a gap, then flex: 1 on the cards themselves so they grow to fill the row.
The value of building these in the generator rather than copying them from memory is that you see the edge cases immediately. A space-between navbar with only one item pins that item to the start, which can look like a bug until you understand that space-between has nothing to distribute with a single item. A wrapping card row behaves differently at two cards versus six, and the preview's adjustable item count lets you check both before you ship. Building the layout by manipulation means the surprising cases surface while you are still in the tool, not after a user reports them.
Once a recipe is in your fingers, you stop needing the generator for it and write the five lines directly. That is the healthy end state. The tool is a teacher as much as a producer: every layout you build by clicking is one you understand a little better the next time you write it by hand, which is exactly how a good visual utility should make itself gradually unnecessary for the basics while staying handy for the fiddly cases.
FAQ
What is a CSS flexbox generator?
A CSS flexbox generator is a visual tool that lets you set flex container properties and copy the resulting CSS. You adjust justify-content, align-items, direction, wrap and gap, see a live preview, and paste the generated rule into your stylesheet.
How do I centre a div with flexbox?
Set the container to display: flex, then justify-content: center and align-items: center. That centres the items on both the main and cross axes. In this tool, choose center for both alignment controls and copy the CSS.
What is the difference between justify-content and align-items?
justify-content distributes items along the main axis, which is horizontal for a row and vertical for a column. align-items positions items on the cross axis, perpendicular to the main axis. Changing flex-direction swaps which axis each one controls.
When does align-content have an effect?
align-content only affects layout when items wrap onto more than one line, because it spaces those lines apart on the cross axis. With flex-wrap set to nowrap there is a single line, so the property does nothing and this tool omits it from the output.
What does the gap property do in flexbox?
gap sets a consistent space between flex items without adding margins to each item. It applies between items on the same line and between wrapped lines, and it avoids the edge-margin problems that margin-based spacing creates.
What is the difference between flex and inline-flex?
display: flex makes the container a block-level box that takes the full available width. display: inline-flex makes it an inline-level box that sits in the text flow and is only as wide as its content, while both lay out their children with the same flex rules.
Does flexbox replace CSS Grid?
No. Flexbox is a one-dimensional model for laying items along a single axis, ideal for toolbars, navigation, and rows of cards. CSS Grid is two-dimensional for rows and columns together. They are complementary and often used in the same layout.
Is the generated CSS safe to use in production?
Yes. Flexbox is supported in every modern browser and the tool emits standard, unprefixed CSS properties. All processing happens in your browser, so nothing is uploaded and the tool works offline once loaded.
