SUMMARY
Purpose: Edge Case Mapping helps teams proactively surface unexpected or uncommon user scenarios and assess their design implications before they cause friction or failure.
Design Thinking Phase: Define → Ideate
Time: 45–60 min session + 1–2 hours analysis
Difficulty: ⭐⭐
When to use:When refining user flows ahead of high-fidelity prototypingWhen preparing a product for real-world launch under varied edge conditionsWhen aligning cross-functional teams on risk tolerance and coverage strategy
What it is
Edge Case Mapping is a UX analysis method used to identify non-happy-path scenarios—cases where edge users, rare behaviours, system limits, or unintended inputs could lead to breakdowns or undesirable outcomes. The goal is to define, not necessarily fix, these cases to better stress-test your design and make informed prioritisation decisions.
📺 Video by NNgroup. Embedded for educational reference.
Why it matters
We often optimise designs around the "ideal" user and flow—but real users don’t follow scripts. Edge Case Mapping gives your team a lens to explore how systems respond to failures, fringe behaviours, and abnormal data. It builds resilience into your product thinking and reduces downstream support, bugs, and reputational risk post-launch.
When to use
- Early in the design process, to map assumptions and prevent unscalable complexity
- Before handover to engineering, ensuring identified gaps are documented (if not resolved)
- During accessibility or internationalisation efforts, to account for variation in behaviour and usage constraints
Benefits
- Rich Insights: Helps uncover user needs that aren’t visible in metrics.
- Flexibility: Works across various project types and timelines.
- User Empathy: Deepens understanding of behaviours and motivations.
How to use it
- Choose a flow or interaction to analyse (e.g., onboarding, checkout, password reset).
- Write out the ideal “happy path” clearly so everyone aligns on the baseline experience.
- Brainstorm edge types:
- User-driven edge cases (e.g., misuse, multilingual input, accessibility needs)
- System-driven edge cases (e.g., server timeout, unexpected data combinations)
- Contextual edge cases (e.g., limited connectivity, device constraints)
- Map them alongside the flow—either visually or as annotated notes—identifying likely outcomes and severity.
- Discuss what to flag, fix, deprioritise, or monitor. Be explicit about trade-offs.
- Document these discussions in your design artefacts (e.g., flow annotations, Jira issues, confluence notes).
Example Output
Flow: Online Grocery Checkout
- Happy Path: Add items → View cart → Choose delivery time → Enter payment → Confirm order
- Edge Case 1: User adds 60 bananas accidentally (fat-finger input)
- Edge Case 2: Payment fails due to expired card
- Edge Case 3: User is colourblind and misses the “Confirm” CTA (design contrast fail)
- Edge Case 4: Cart session expires during payment
Each noted with proposed design guardrail (e.g., quantity limit, duplicate card prompt, accessibility audit, session warning timer).
Common Pitfalls
- Avoiding ambiguity: Designers often skip uncertain edge cases. Define them even if you don't have a solution yet.
- Overengineering: Not every edge case needs a fix; many just need sensible defaults or calm failure states.
- Ignoring user intent: Not all odd behaviours are errors—some edge cases reveal underserved needs. Explore them.
10 Design-Ready AI Prompts for Edge Case Mapping – UX/UI Edition
How These Prompts Work (C.S.I.R. Framework)
Each of the templates below follows the C.S.I.R. method — a proven structure for writing clear, effective prompts that get better results from ChatGPT, Claude, Copilot, or any other LLM.
C.S.I.R. stands for:
- Context: Who you are and the UX situation you're working in
- Specific Info: Key design inputs, tasks, or constraints the AI should consider
- Intent: What you want the AI to help you achieve
- Response Format: The structure or format you want the AI to return (e.g. checklist, table, journey map)
Level up your career with smarter AI prompts.Get templates used by UX leaders — no guesswork, just results.Design faster, research smarter, and ship with confidence.First one’s free. Unlock all 10 by becoming a member.
Prompt Template 1: “Identify Hidden Risks in a Flow”
Identify Hidden Risks in a Flow
Context: You are a UX designer reviewing a checkout flow on a native mobile app.
Specific Info: The flow has five key steps and has known drop-offs at the payment and confirmation stages. The team is preparing for international rollout.
Intent: Surface possible edge cases (technical, behavioural, accessibility-based) that could impact flow success.
Response Format: Provide a list of edge cases by flow step with risk level and mitigation options.
If key stages are unclear or missing, ask for clarification.
Then, suggest one idea for how to test one of these edge scenarios before launch.
Prompt Template 2: “Generate Edge Case Questions for Team Workshops”
Generate Edge Case Questions for Team Workshops
Context: You're a lead designer facilitating a cross-functional ideation session.
Specific Info: Focus is on onboarding flow for a fintech app used by first-time investors.
Intent: Create a diverse set of “what if” scenario prompts to trigger edge case thinking across roles.
Response Format: Return a set of discussion questions grouped by user-driven, system-driven, and context-driven scenarios.
Ask for clarification on risk appetite if necessary.
Then, suggest one way to visualise the edge cases generated by the session.
Prompt Template 3: “Audit Your Flow for ‘Error States’ Across Devices”
Audit Your Flow for ‘Error States’ Across Devices
Context: You’re finalising designs for a responsive web flow used on phones, tablets, and desktop.
Specific Info: The signup process uses modal overlays and real-time form validation.
Intent: Identify device-specific interaction risks that could break the flow or confuse the user.
Response Format: Provide a table listing potential device issues, trigger conditions, and suggested design checks.
Ask which devices or viewports are most critical if unknown.
Recommend one responsive pattern or fallback approach to evaluate further.
Prompt Template 4: “Stress-Test Input Fields Against Real-World Data”
Stress-Test Input Fields Against Real-World Data
Context: You’re designing forms for a global marketplace platform.
Specific Info: You have inputs for name, address, phone number, and product description.
Intent: Identify input edge cases across cultural, technical, and linguistic variation.
Response Format: Provide a list of test strings and formats to validate robustness and inclusivity.
Ask which countries or user cohorts matter most if unclear.
Recommend language inclusion habits or localisation checks to continue exploring.
Prompt Template 5: “Contrast Failure Modes vs. Graceful Degradation”
Contrast Failure Modes vs. Graceful Degradation
Context: You are reviewing network-limited usage scenarios for a video streaming feature.
Specific Info: Auto-play, buffering spinners, and progressive loading are used.
Intent: Explore how the experience behaves under poor connectivity or partial errors.
Response Format: Summarise key failure modes and propose alternative states for each (e.g. interstitial, toast, fallback UX).
Ask whether exact latency ranges are known.
Then, suggest ways to prototype one failure scenario using Figma or code.
Prompt Template 6: “Design a Team Edge Case Radar Map”
Design a Team Edge Case Radar Map
Context: You are helping your team systematically map known design blind spots.
Specific Info: Team includes PMs, engineers, and data science. Project involves machine learning predictions.
Intent: Co-create a radar or quadrant diagram showing edge conditions and how well they’re covered.
Response Format: Return a suggested layout, sample categories, and coverage attributes.
Ask about available past incident data or logs if helpful.
Invite the team to vote on the riskiest quadrant to explore further.
Prompt Template 7: “Probe Accessibility-Related Edge Cases”
Probe Accessibility-Related Edge Cases
Context: You are auditing a B2B dashboard with complex tables, modals, and filters.
Specific Info: WCAG checklist has been run but not user tested.
Intent: Identify potential accessibility edge cases based on interaction complexity.
Response Format: Provide a list of questions and heuristics to pressure test the interface for screen readers, keyboard use, and low vision users.
Ask what assistive tech KB is in use if unsure.
Suggest one persona or scenario to prototype for in next cycle.
Prompt Template 8: “Diagnose Behavioural Edge Cases in Metrics”
Diagnose Behavioural Edge Cases in Metrics
Context: You are reviewing analytics for a feature rolled out to 20% of users.
Specific Info: Unexpected drop-off seen in a specific geo and device cohort.
Intent: Propose user scenarios or edge behaviours that might explain the data.
Response Format: Return three potential user stories or mental models that match the observed metric pattern.
Ask for session recording availability if known.
Propose one micro-survey question to test the hypothesis.
Prompt Template 9: “Simulate Cross-Boundary System Edge Cases”
Simulate Cross-Boundary System Edge Cases
Context: You're working on a multi-service platform involving identity, payments, and notifications.
Specific Info: Different subsystems fail independently and have latency mismatches.
Intent: Identify cross-service edge cases and user-facing effects.
Response Format: Provide sequence diagrams or interaction breakdown showing what fails and when.
Request system owner clarification if integrations are unclear.
Then, suggest a fallback pattern or systemic rule to apply.
Prompt Template 10: “Build an Edge Case Capture Table for Designers”
Build an Edge Case Capture Table for Designers
Context: You’re preparing team documentation for a redesign project.
Specific Info: Your designers need a template to consistently capture edge cases by screen/flow.
Intent: Provide a table they can copy-paste into Figma or Confluence.
Response Format: Structured table with columns for Step, Triggered by, Impact, Proposed Handling, Owner.
Ask what formats the team already uses for notes or decisions.
Then, suggest a template smart component or sticky structure for Figma/Jamboard.
Recommended Tools
- Figma – for mapping flows and annotating edge cases visually
- Contrast Checker – for quickly validating visual accessibility edge cases
- ChatGPT – to generate edge case prompts, test strings, and recap scenarios
- Axe DevTools – advanced edge testing for accessibility breakdowns
