Debugging with Claude Code: Beyond "Fix This Bug"
Why Most Developers Debug Wrong with AI
Why Most Developers Debug Wrong with AI
The most common way developers use AI for debugging is: paste the error, ask for a fix, apply the suggestion, and hope it works. This is the worst way to use Claude Code for debugging.
Claude Code is not a Stack Overflow replacement. It is an investigative tool. The difference is profound. Stack Overflow gives you an answer to a known problem. Claude Code can investigate an unknown problem — reading logs, tracing execution paths, checking state management, and narrowing down the root cause before suggesting a fix.
The developers who debug effectively with Claude Code treat it like a detective, not an oracle.
The Investigation Workflow
Here is my debugging workflow with Claude Code. It is methodical, and it works on bugs that range from simple typos to complex race conditions.
Step 1: Describe the Symptom, Not the Diagnosis
# Bad
me: The useEffect dependency array is wrong, fix it
# Good
me: When I navigate from the Products page to the Dashboard and back,
the product filters reset to their defaults. They should persist.
The filters are managed in useProductFilters hook. The Products
page is at app/products/page.tsx.
The first prompt assumes you already know the root cause (and you might be wrong). The second prompt describes what you observe and lets Claude Code investigate.
Step 2: Let Claude Code Investigate
After describing the symptom, Claude Code will:
- Read the relevant files (useProductFilters, the Products page, the navigation setup)
- Trace the state lifecycle (where is state initialized? When is it destroyed?)
- Identify the root cause (maybe the hook reinitializes because the component unmounts during navigation)
- Propose a fix that addresses the root cause, not just the symptom
This is more thorough than jumping to a fix because Claude Code checks the entire chain, not just the immediate site of the bug.
Step 3: Verify with Reproduction
me: Before fixing, explain what you think is happening step by step.
What is the sequence of events that causes the filters to reset?
This step is critical. It forces Claude Code to articulate its understanding, and it lets you verify that understanding before any code changes. If Claude Code's explanation does not match your observations, you can correct it before it goes down the wrong path.
Step 4: Fix and Verify
me: That explanation makes sense. Fix the issue and write a test that
would have caught this bug. The test should verify that filters
persist across navigation.
Including the test ensures the bug stays fixed. It also validates that Claude Code's understanding is correct — if the test cannot reproduce the bug, the diagnosis might be wrong.
Debugging Patterns for Common Frontend Issues
The Render Cycle Detective
React rendering issues are notoriously hard to debug because the symptoms (flickering, stale data, infinite loops) can have many causes.
me: The UserDashboard component is re-rendering on every keystroke in
the search bar, even though the search bar is in a completely
different component (SearchHeader). They share no direct props.
Investigate:
1. Check if there is a shared context that both components consume
2. Check if a parent component re-renders and forces both to re-render
3. Check if there is a Zustand store subscription that is too broad
4. Add console.log markers if needed to trace the render chain
Do NOT just add React.memo everywhere — find the actual cause.
The key instruction is "Do NOT just add React.memo everywhere." Without this, Claude Code might apply a band-aid instead of finding the real issue.
The Type Mismatch Investigator
TypeScript errors in complex codebases often have non-obvious root causes:
me: I am getting this TypeScript error:
Type '{ data: Product[]; isLoading: boolean; }' is not assignable
to type 'UseQueryResult<Product[], Error>'.
This started after updating @tanstack/react-query from 5.17 to 5.28.
Check what changed in the TanStack Query types between these versions.
Look at our custom useQuery wrapper in hooks/useQuery.ts to see if
it needs to be updated.
Do NOT use 'as' type assertions — fix the types properly.
The State Synchronization Debugger
State bugs where two pieces of state get out of sync are among the hardest to track down:
me: Bug: The cart total shows $150 but the individual items add up to $120.
The cart state is in stores/cartStore.ts.
Cart items are in the items array.
The total is computed by a getTotal getter.
Investigate:
1. Is the total being computed correctly from the current items?
2. Is there a stale closure capturing an old items array?
3. Are there multiple sources of truth for the cart items?
4. Is there a race condition in the add/remove item actions?
5. Check if the total updates when items change or if it is cached incorrectly
The CSS Layout Detective
CSS bugs are uniquely frustrating because the symptom (visual) does not directly map to the cause (declarative properties). Claude Code can help by reading the component structure and analyzing the cascade:
me: The sidebar overlaps the main content on screens between 768px and
1024px. On smaller screens it collapses correctly. On larger screens
it sits beside the content correctly. Only the tablet range is broken.
The layout is in components/layout/AppLayout.tsx.
Sidebar is components/layout/Sidebar.tsx.
Using Tailwind for all styling.
Check the responsive breakpoints and the flex/grid configuration.
Look for conflicting width classes at the md: breakpoint.
The Network Request Debugger
When API calls behave unexpectedly:
me: The PUT /api/projects/:id endpoint returns 200 but the UI does not
update with the new data. The user has to refresh the page to see
the changes.
Relevant files:
- services/projects.ts (updateProject function)
- hooks/useUpdateProject.ts (mutation hook)
- components/projects/ProjectDetail.tsx (displays and edits)
Check:
1. Is the mutation returning the updated data?
2. Is TanStack Query cache being invalidated after the mutation?
3. Is the optimistic update reverting and not being replaced?
4. Are there multiple query keys for the same data that are not
all being invalidated?
Advanced Debugging Techniques
The Bisect Approach
When you do not know when a bug was introduced:
me: The login redirect is broken — after login, users land on /dashboard
instead of the page they were trying to access.
I know this worked as of commit abc123 (last Thursday).
Check the git log between abc123 and HEAD for changes to:
- auth middleware
- login flow
- routing configuration
- redirect logic
Narrow down which commit introduced the regression.
Claude Code reads the git history, identifies relevant commits, and traces the change that broke the redirect. This is faster than manual git bisect because Claude Code can read the diffs intelligently.
The Environment Detective
When a bug appears in one environment but not another:
me: The image upload works in development but fails in production with
a 413 error. Both environments use the same code.
Check:
1. Environment-specific configuration (upload size limits)
2. Next.js config differences between dev and production
3. Middleware that might apply different limits
4. The Vercel deployment configuration
5. Our API route configuration for the upload endpoint
The Memory Leak Hunter
me: The analytics dashboard page gets progressively slower the longer
it is open. After about 10 minutes, interactions become noticeably
laggy. The page auto-refreshes data every 30 seconds.
Investigate potential memory leaks:
1. Check all useEffect hooks for missing cleanup functions
2. Check WebSocket or EventSource subscriptions
3. Check if chart libraries are properly destroying old instances
4. Check if TanStack Query is accumulating stale cache entries
5. Look for DOM elements being created but not removed
The Debugging Mindset
The pattern across all these examples is the same: describe the symptom thoroughly, provide context about what should happen versus what does happen, point to the relevant files, and ask for investigation before fixes.
Claude Code is most effective as a debugging tool when you resist the urge to jump to "fix it." The investigation phase is where the value is. A wrong fix applied quickly just creates a new bug. A correct diagnosis, even if it takes longer, leads to a fix that actually solves the problem.
The best debugging sessions I have with Claude Code are conversations, not commands. "Here is what I see." "Here is what I think might be happening." "What do you find when you look at the code?" This collaborative approach produces better results than treating AI as a vending machine for solutions.