Whether you are testing a new application or running regression checks against an established website, knowing where defects commonly appear can save time and improve coverage.
The following 20 checks cover some of the most frequent and highest-impact website bugs a QA tester is likely to encounter.
1Broken links
Broken navigation frustrates users and can damage trust in the website. Test internal links, external links, buttons and redirects.
- Links opening a 404 page
- Buttons pointing to the wrong destination
- External resources that no longer exist
- Redirect loops or unexpected redirects
2Missing form validation
Forms should reject invalid data and explain what the user needs to fix.
- Required fields accepting empty values
- Invalid email addresses being accepted
- Letters entered into numeric fields
- Passwords ignoring complexity requirements
3Unclear error messages
Error messages should help the user recover. Generic text such as “Something went wrong” or raw server errors rarely provides enough guidance.
4Mobile responsiveness issues
Test across common viewport sizes rather than relying on a single desktop screen.
- Cut-off text or buttons
- Horizontal scrolling
- Images overflowing their containers
- Tap targets positioned too closely together
5Accessibility defects
Accessibility testing helps ensure the website can be used by people relying on keyboards, screen readers and other assistive technologies.
- Missing alternative text
- Inputs without visible labels
- Poor colour contrast
- Missing keyboard focus indicators
- Incorrect heading structure
Read our guide to WCAG compliance for a deeper introduction.
6Browser compatibility bugs
Features that work in one browser may behave differently in another. Test key journeys in Chrome, Edge, Firefox and Safari where applicable.
7Session timeout problems
Users should not lose work unexpectedly or remain signed in longer than intended.
- Sessions expiring without warning
- Remember Me behaving incorrectly
- Logout not invalidating the session
- Different tabs showing inconsistent session states
8Duplicate submissions
Rapidly clicking Save or Submit should not create duplicate records, payments, orders or messages.
- Double-clicking the primary action
- Refreshing after submission
- Using the browser Back button and submitting again
9Slow loading performance
Pages that take too long to load can cause users to abandon the website.
- Oversized images
- Blocking scripts
- Repeated or unnecessary API calls
- Long-running database queries
10Search defects
Search functionality should return relevant and predictable results.
- Partial matches not returned
- Special characters breaking the search
- Empty searches causing errors
- Filters or search types being ignored
11Incorrect sorting
Sorting should use the correct data type. Text-based sorting can produce unexpected results for dates, numbers and currency values.
12Filtering problems
Test each filter individually and in combination with other filters.
- Reset buttons not clearing selections
- Multiple filters producing incorrect results
- Pagination losing the selected filters
- No-results messages displaying incorrectly
13Date and time bugs
Date handling is a common source of defects, especially where users, servers and integrated systems use different time zones.
- Incorrect regional formats
- Time-zone offsets
- Leap-year errors
- Invalid dates such as 31 February
- Daylight-saving changes
14File upload errors
File upload controls require more testing than simply attaching a valid file.
- Unsupported file types
- Files exceeding the size limit
- Duplicate uploads
- Interrupted or failed uploads
- Unsafe filenames or extensions
15Security validation weaknesses
QA testers should perform appropriate security checks without relying solely on the interface.
- Cross-site scripting attempts
- SQL injection-style inputs
- URL and parameter manipulation
- Sensitive information exposed in responses or logs
16Poor API error handling
The website should remain understandable and usable when an API request fails.
- 400 validation responses
- 401 and 403 permission responses
- 404 missing-resource responses
- 500 server failures
- Timeouts and unavailable services
17Navigation defects
Navigation should remain consistent across pages, devices and user states.
- Incorrect menu items
- Missing breadcrumbs
- Unexpected browser Back behaviour
- Pages that cannot be reached through the interface
18Permission issues
Hiding an action in the interface is not enough. Users should also be prevented from performing restricted actions through direct URLs or API calls.
- Administrator pages accessible to standard users
- Disabled actions still available through another route
- Users accessing another user’s records
- Permissions not updating after a role change
19Data persistence problems
Confirm that saved information remains correct after the surrounding state changes.
- Refreshing the page
- Logging out and returning later
- Closing and reopening the browser
- Editing related records
- Restarting the application or service
20Visual and UI defects
Presentation bugs may not stop functionality, but they can make the product appear unreliable or difficult to use.
- Misaligned elements
- Overlapping or clipped text
- Missing icons
- Inconsistent spacing
- Unexpected fonts, colours or component states
Final website testing checklist
- Navigation works correctly
- Forms validate invalid data
- Mobile layouts remain usable
- Accessibility checks are complete
- Security inputs are handled safely
- Performance is acceptable
- Saved data persists correctly
- Permissions are enforced
- API failures are handled clearly
- The interface is visually consistent
Final thoughts
Good QA is not about clicking every button without a plan. It is about understanding where software is most likely to fail and applying targeted checks around risk, data, user behaviour and integrations.
By including these 20 checks in your regular testing routine, you can catch many of the website defects most likely to affect real users before they reach production.