2.5.1 - Complex gestures

Do not require complex gestures or using more than one finger to do things.

Summary

Make sure that users can do everything without needing to use multi-touch (like pinching, or swiping with several fingers), or following a complex path with their finger.

Requirements

If a feature requires the user of several fingers at the same time, make sure that the user interface offers another way to achieve the same result using just one finger.
If a feature requires users to drag a finger along a path that's more complex than just going directly from A to B, make sure that the user interface offers another way to achieve the same result without needing to do that.

Common mistakes

Requiring users to perform complex gestures to do things.
Requiring users to use several fingers at the same time.

Why?

Some disabled users may need simple inputs or gestures to complete tasks and make selections. Complex movement or gestures requiring dexterity or accuracy may be hard for them.

Official wording in the Web Content Accessibility Guidelines

2.5.1 Pointer Gestures: All functionality that uses multipoint or path-based gestures for operation can be operated with a single pointer without a path-based gesture, unless a multipoint or path-based gesture is essential. (Level A)

See the W3C's detailed explanation of this guideline with techniques and examples.

Guidance for Design

Examples

Google Maps uses a 'pinch-to-zoom' gesture. But the same result can be achieved by clicking the '+' button.
macOS has trackpad gestures that use several fingers. But the same results can be achieved using just the mouse.