Fluid Typography

Let type grow smoothly with the viewport instead of jumping at every breakpoint.

moderate Design Systems

What it adds

Viewport-interpolated sizing for the existing type steps, bounded by a defined floor and ceiling.

What your agent is told to do

1
Apply interpolation to the steps already defined by Typography Scale rather than inventing new sizes. That feature owns which steps exist; this one owns how each one behaves between the narrowest and widest viewport.
2
Give every fluid step an explicit minimum and maximum. An unbounded rule produces unreadable type on a small phone and absurd type on an ultrawide monitor, and both ends will be found by real users.
3
Scale the display and heading steps more aggressively than body copy. Body text has a comfortable size that does not change with the window, and growing it with the viewport makes wide screens harder to read, not easier.
4
Adjust line height as the size changes — large type wants proportionally tighter leading than small type — otherwise headings that looked correct on a phone become airy and loose on a desktop.
5
Do not express the interpolation purely in viewport units. A size that ignores the root font size stops responding to browser zoom and to the user's own text-size preference, which is a straightforward accessibility failure.

Edge cases it handles

Every fluid step needs a clamped floor and ceiling, since the interpolation is a straight line and will happily continue past the point of legibility in both directions.
Sizes derived from viewport units alone do not respond to browser zoom, so the setting a low-vision user relies on stops working exactly where they need it.
Line height must be interpolated alongside size, or the leading that suited the smallest step leaves large headings looking disconnected from themselves.
Large display steps set for a desktop hero will overwhelm a narrow screen and wrap into four lines, so the floor for those steps needs to be much lower than their proportional value suggests.
Interpolation driven by the viewport misbehaves inside constrained columns, sidebars, and dialogs, where the available width has nothing to do with the window width.
Text that resizes continuously during a window drag or a device rotation causes reflow of everything below it; verify that nothing measured in a fixed pixel height sits beside fluid text.
Values that land on fractional pixels can render inconsistently across browsers, so check the interpolated sizes at real viewport widths rather than only at the two endpoints.

Definition of done

Type sizes change continuously across viewport widths with no jump at a breakpoint.
Every fluid step has an enforced minimum and maximum size.
Type still responds correctly to browser zoom and user text-size settings.
Line height is interpolated together with size at every step.
Body copy scales conservatively while display steps scale more.
Headings do not overflow or wrap awkwardly at the narrowest supported width.
The step definitions themselves remain owned by Typography Scale.
The feature matches the existing design system.
No existing functionality is broken.

Related features

Z-Index Registry

Spacing Scale

Shadow Scale

How it works

1

Copy the link

Grab the Markdown instruction URL for this feature.
2

Give it to your AI

Paste it into Claude Code, Cursor, v0, Lovable — whatever you build with.
3

It inspects, then implements

Your agent reads your existing app first, then adds the feature to fit it.

Works with your stack

These instructions are written to adapt. They tell the agent to detect your framework, match your existing design system, and reuse what you already have — rather than assuming a particular stack.

Need it tighter than that? Customize the feature and tell it exactly what you're running.