usability-check

name	usability-check
description	Evaluate user-facing interfaces against Nielsen's 10 Usability Heuristics. Complements /mycelium:service-check (Downe = service-level quality, Nielsen = interface-level quality).
metadata	{"instruction_budget":"45","framework_dependency":"mycelium","framework_dependency_note":"This skill is designed to run within the Mycelium framework (https://github.com/haabe/mycelium). Standalone use will skip the canvas state, theory gates, and harness behavior the skill assumes. Install: /plugin install mycelium@haabe/mycelium."}

Usability Heuristic Evaluation

Evaluate interface-level usability using Jakob Nielsen's 10 heuristics (1994). This complements Downe's 15 Good Services principles: Downe checks end-to-end SERVICE quality, Nielsen checks screen-level INTERFACE quality. Both are needed for user-facing work.

When to Use

• During L4 Delivery for any user-facing work (REVIEW via G-V10)
• After UI implementation, before marking delivery complete
• When users report confusion or friction

The 10 Heuristics

1. Visibility of System Status

The system should always keep users informed about what is going on through timely and appropriate feedback.

• Loading states visible for any operation > 1 second
• Progress indicators for multi-step processes
• Success/failure feedback for user actions
• Current location/state clearly indicated (breadcrumbs, active nav)

2. Match Between System and Real World

The system should speak the users' language, using familiar words, phrases, and concepts rather than system-oriented terms.

• No technical jargon in user-facing text
• Familiar icons and metaphors
• Information in natural, logical order
• Real-world conventions followed (calendar = dates, cart = shopping)

3. User Control and Freedom

Users often perform actions by mistake. They need a clearly marked "emergency exit" to leave the unwanted action.

• Undo/redo available for destructive actions
• Cancel option in all multi-step flows
• Back button works as expected
• Easy to return to a known state

4. Consistency and Standards

Users should not have to wonder whether different words, situations, or actions mean the same thing.

• Same action = same word everywhere (don't mix "delete" and "remove")
• Platform conventions followed (OS patterns, web standards)
• Internal consistency (same patterns across all screens)
• Visual consistency (colors, typography, spacing)

5. Error Prevention

Even better than good error messages is a careful design that prevents problems in the first place.

• Confirmation before destructive actions
• Constraints that prevent invalid input (date pickers vs free text)
• Disabled states for unavailable actions (not hidden, not error-on-click)
• Autosave or draft state for long forms

6. Recognition Rather Than Recall

Minimize the user's memory load by making elements, actions, and options visible.

• Recently used items visible/accessible
• Labels on icons (not icon-only buttons)
• Options visible in menus (not hidden behind gestures)
• Help text near complex fields

7. Flexibility and Efficiency of Use

Accelerators — unseen by the novice user — may speed up the interaction for the expert user.

• Keyboard shortcuts for frequent actions
• Search/filter for large lists
• Customizable settings for power users
• Both simple and advanced paths available

8. Aesthetic and Minimalist Design

Dialogues should not contain information that is irrelevant or rarely needed.

• Every element serves a purpose
• No decorative clutter competing with content
• Important information has visual priority
• Whitespace used to group and separate

9. Help Users Recognize, Diagnose, and Recover from Errors

Error messages should be expressed in plain language, precisely indicate the problem, and constructively suggest a solution.

• Error messages in plain language (not codes)
• Error messages say WHAT went wrong
• Error messages suggest HOW to fix it
• Errors visually connected to the field/action that caused them

10. Help and Documentation

Even though it is better if the system can be used without documentation, it may be necessary to provide help.

• Help is searchable
• Help is task-oriented (not feature-oriented)
• Help is concise and actionable
• Contextual help available where needed (tooltips, inline)

Complementary: interaction & visual axioms (optional, nudge-only)

Nielsen's heuristics are diagnostic principles. They do not cover the quantitative interaction-design layer: Fitts's/Hick's target-and-choice math, Gestalt grouping (proximity, similarity, closure, common-region), typography (line-length/CPL, line-height, F-pattern scanning), and cognitive-load laws. If this project has a UI surface and the user wants that layer, the haabe/ux-axioms-mcp server covers it. Per its README, the server exposes ~44 such axioms with analyze_ui / suggest_axioms / generate_spec / generate_tests tools — confirm the current install/run path against the repo before recommending a specific setup command.

Mycelium nudges, never installs: offer it, let the user wire it up (per ${CLAUDE_PLUGIN_ROOT}/harness/design-principles.md — autonomy/JIT-tooling). Don't double-surface — where a Nielsen heuristic and an axiom overlap (e.g. heuristic 4 Consistency ↔ Similarity; heuristic 8 Minimalist ↔ Occam's Razor), cite once. The persuasion axioms in that registry are dual-use; the same ethics line as anti-pattern #10 (Dark Pattern Marketing) applies.

Output Format

## Usability Heuristic Evaluation

| Heuristic | Status | Issues |
|-----------|--------|--------|
| 1. Visibility of status | pass/partial/fail | ... |
| 2. Match real world | pass/partial/fail | ... |
| 3. User control & freedom | pass/partial/fail | ... |
| 4. Consistency & standards | pass/partial/fail | ... |
| 5. Error prevention | pass/partial/fail | ... |
| 6. Recognition > recall | pass/partial/fail | ... |
| 7. Flexibility & efficiency | pass/partial/fail | ... |
| 8. Aesthetic & minimal | pass/partial/fail | ... |
| 9. Error recovery | pass/partial/fail | ... |
| 10. Help & documentation | pass/partial/fail | ... |

Overall: [X]/10 passing
Priority fixes: [list most impactful issues]

Theory Citations

• Nielsen: 10 Usability Heuristics for User Interface Design (1994)
• Downe: Good Services (complementary -- service-level, not interface-level)