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Usability

What is usability?

Usability is how easy it is for users to complete tasks with your product: they can learn it, use it efficiently, avoid and recover from errors, and feel satisfied. It’s a quality of the product and the interaction, not a single metric.

Use it when: you’re designing, evaluating, or improving any user-facing product. Usability is a baseline expectation; measure and test it so you’re not guessing.

Copy/paste checklist (five dimensions)

  • Learnability – Can new users accomplish basic tasks the first time?
  • Efficiency – Once learned, can experienced users complete tasks quickly?
  • Memorability – After a break, can users return without relearning?
  • Errors – How often do users err, and how easily can they recover?
  • Satisfaction – Do users find the experience acceptable or pleasant?

Assess with usability testing and, where useful, with standardised questionnaires (e.g. SUS).

Why usability matters

  • When products are usable, people complete tasks faster and with less frustration.
  • Support and training costs go down; satisfaction and retention tend to go up.
  • Poor usability blocks adoption and conversion even when the product is otherwise valuable.
  • Accessibility and usability overlap: fixing one often helps the other.

What good usability includes

Checklist

  • [ ] Clear goals – Users can tell what they can do and how to start.
  • [ ] Obvious actions – Buttons, links, and controls are recognisable and reachable.
  • [ ] Feedback – The system shows state and confirms actions (visibility of system status).
  • [ ] Error prevention and recovery – Sensible defaults, validation, and clear error messages.
  • [ ] Consistency – Patterns and labels are predictable across the product.
  • [ ] Appropriate complexity – No unnecessary steps or clutter for the core tasks.

Common formats

  • Usability testing – Observe users completing tasks; note completion, errors, and comments. See Usability testing.
  • Heuristic evaluation – Expert review against principles. See Heuristic evaluation.
  • SUS (System Usability Scale) – Short questionnaire after a task or session; gives a score. Use to compare versions or track over time.

Examples

Example (the realistic one)

You run a usability test on “create and send an invoice.” Learnability: 4 of 5 complete it first time; 1 gets stuck on “Add line item.” Efficiency: Experienced user takes ~2 minutes (acceptable). Errors: 2 users picked “Draft” instead of “Send” once; they recovered. Satisfaction: Post-task SUS average 72. You prioritise clarifying “Draft” vs “Send” and the “Add line item” step to improve learnability and errors.

Common pitfalls

  • Assuming it’s usable: no testing, only opinion. → Do this instead: run usability testing or heuristic evaluation on key flows.
  • Only testing happy path: you miss errors and edge cases. → Do this instead: include tasks that can fail and observe recovery.
  • Ignoring learnability: you test with people who already know the product. → Do this instead: include new or infrequent users for learnability and memorability.
  • No baseline: you can’t say if things got better. → Do this instead: define tasks and (if possible) a metric (e.g. completion rate, SUS) and repeat after changes.
  • Usability vs UX: UX is the broader experience (including emotion, value, and context); usability is “can they use it effectively and satisfactorily?”. Usability is part of UX.
  • Usability vs accessibility: Accessibility ensures people with disabilities can use the product; usability is about ease and satisfaction for all users. They overlap; do both.
  • Usability vs usability testing: usability is the quality; usability testing is the method to evaluate it.

Next step

Pick one critical task, run a usability test with 5 users, and score the five dimensions (learnability, efficiency, memorability, errors, satisfaction). Fix the biggest issues and test again to see improvement.

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