Scientific category · 18 concepts

Usability principles and heuristics

Practical principles for clarity, simplicity, error resistance, visibility, and consistency that come from HCI practice rather than one experiment.

Questions this category answers

Can people understand the system state?
Can they recover?
Does simplification preserve what the task requires?

Research context: Human computer interaction and usability engineering

Reference set

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Two controls with the same function where the more visually coherent control receives the stronger perceived quality signal.

Usability

Aesthetic-Usability Effect

People often judge a visually coherent interface as easier to use, especially before or during early interaction.

A system blueprint connects hidden system parts to the visible interface structure presented to users.

Usability

Conceptual Models

A conceptual model is the designed explanation of a system’s objects, relationships, actions, and state that the interface presents to users.

A guided path leaves valid actions open while visibly blocking invalid branches.

Usability

Constraints Principle

Well-designed constraints limit invalid actions or make their boundaries clear while preserving valid choice and recovery.

A visible object moves directly with a handle and shows both its new position and a reversible path.

Usability

Direct Manipulation

Direct manipulation lets people act on visible objects through incremental, rapid, and reversible operations with immediate feedback.

An input pulse receives a nearby response pulse before a waiting gap opens.

Usability

Doherty Threshold

Rapid, meaningful system feedback helps sustain an interactive rhythm; the often-cited 400 ms value is historical guidance, not a universal boundary.

The same simple task appears once behind distracting interface noise and once in a clear presentation.

Usability

Extraneous Cognitive Load

Extraneous cognitive load is mental work caused by how information or a task is presented rather than by the relationships that must be learned.

A user action triggers an immediate state response followed by a clear completion response.

Usability

Feedback Principle

Every meaningful action should produce timely, perceivable feedback that accurately communicates the resulting system state.

A sequence of link cues becomes more specific as it leads toward a desired information goal.

Usability

Information Scent

Information scent is the perceived value of a cue for predicting whether a path will lead toward the information a person seeks.

Three interface frames share the same navigation pattern while a fourth moves the familiar control.

Usability

Jakob’s Law

People bring expectations learned from other products, so familiar conventions often reduce the effort needed to begin using a new interface.

A simplified internal map is compared with a more detailed system map, with aligned and mismatched paths.

Usability

Mental Models

A mental model is a person’s internal, partial representation of how a system works and what actions will produce.

Several routes reach the same result, with unnecessary branches removed from the simplest sufficient path.

Usability

Occam’s Razor

When explanations or designs account for the same requirements equally well, prefer the one that depends on fewer unnecessary assumptions.

A few inputs contribute most of an outcome while many inputs contribute smaller amounts.

Usability

Pareto Principle

Outcomes are often unevenly distributed, so a minority of causes, tasks, or defects may account for a large share of observed impact.

The same task block stretches to fill a larger available time container.

Usability

Parkinson’s Law

Work can expand to occupy the time made available, making bounded scope and explicit completion criteria useful planning constraints.

Several input formats approach a validation gate, which accepts safe variation and rejects an invalid input.

Usability

Postel’s Law

Accept safe, unambiguous input variation where useful and produce predictable output, while rejecting ambiguity that threatens security or interoperability.

A simple initial interface opens into two deeper layers of detail as needed.

Usability

Progressive Disclosure

Progressive disclosure presents the information and controls needed now, then reveals additional detail when the user asks or the task reaches it.

A blank recall field is contrasted with a set of visible recognizable options.

Usability

Recognition Rather Than Recall

Make relevant objects, actions, and options visible or readily retrievable so people do not have to recall them unaided.

A control gains a clear label, boundary, and directional cue that indicate how it can be used.

Usability

Signifiers

Signifiers are perceivable cues that communicate where an action can occur, how to perform it, or what state an object is in.

A fixed complexity weight shifts between the system side and the user side of a balance.

Usability

Tesler’s Law

Some task complexity is irreducible, so design determines whether the system, the user, or an organization carries that work.

Explore another category

InteractionHuman factors, motor control, and human computer interaction GestaltGestalt psychology and perceptual organization PerceptionVisual perception, psychophysics, and information visualization AttentionCognitive psychology and attention research MemoryMemory science, learning science, and cognitive psychology Cognitive loadCognitive load theory, problem solving, and interface complexity