How to Debug Code with Claude Code

Stop staring at cryptic error messages. Learn how to use Claude Code to understand errors, trace bugs, and fix issues faster than traditional debugging.

To debug code with Claude Code, paste the full error message into your terminal, and Claude will explain it in plain English, trace the root cause through your codebase, and suggest or apply the fix directly. It works for syntax errors, runtime exceptions, logic bugs, and complex multi-file issues across any language or framework.

What used to mean hours of searching Stack Overflow and adding print statements now takes minutes. This guide walks you through the complete debugging workflow, from copying the error to verifying the fix.

What Is Debugging with Claude Code?

Debugging with Claude Code means using AI to help you understand and fix errors in your code. Instead of manually searching for solutions, you give Claude the error message and context, and it:

• Explains the error in plain English
• Identifies the root cause by reading your actual code
• Suggests fixes with explanations of why they work
• Implements the fix if you approve it
• Verifies the solution by running tests or checking for regressions

This works for any type of bug: syntax errors, runtime exceptions, logic bugs, performance issues, and integration problems.

Step-by-Step Debugging Process

Here is the workflow that works for most debugging scenarios:

Reading Error Messages with Claude

The most common debugging workflow is pasting an error and asking Claude to help. Here is how to do it effectively:

I got this error when running npm start:

TypeError: Cannot read properties of undefined (reading 'map')
    at ProductList (src/components/ProductList.jsx:12:23)
    at renderWithHooks (node_modules/react-dom/...)

What does this mean and how do I fix it?

This API endpoint returns a 500 error:

Error: SQLITE_CONSTRAINT: UNIQUE constraint failed: users.email
    at Database.exec (/app/node_modules/better-sqlite3/...)

I expected it to update the existing user's email, not fail.
The endpoint is PUT /api/users/:id

This error happens randomly, maybe 1 in 10 requests:

TimeoutError: Navigation timeout of 30000 ms exceeded

It seems to happen more often when the server is under load.
Here's the code that triggers it: @src/scraper/navigate.js

What could cause intermittent timeouts?

Pipe Errors Directly to Claude

Instead of copying and pasting error messages, you can pipe your terminal output directly to Claude Code. This creates a live feed that Claude can analyze as errors happen:

# Pipe test failures directly to Claude
npm run test 2>&1 | claude -p "Fix these failing tests"

# Pipe build errors
npm run build 2>&1 | claude -p "Fix these TypeScript build errors"

# Create a reusable shell function
# Add to ~/.zshrc or ~/.bashrc:
ask() { "$@" 2>&1 | claude -p "Analyze this output and suggest fixes." }

Then simply run ask npm run test to send any command's output to Claude for analysis. For large outputs, consider piping through tail first: npm run test 2>&1 | tail -100 | claude -p "Fix these test failures".

Use the Built-in Debugger Agent

Claude Code has a built-in Explore subagent that handles read-only codebase analysis using Haiku 4.5 for speed. For debugging, you can also create a dedicated debugger agent that follows your team's diagnostic workflow. Custom agents run in their own context window, keeping verbose debug output separate from your main conversation.

To see your available agents, run /agents in Claude Code. To create a custom debugger agent, select "Create new agent" and describe a debugging workflow. See our custom agents guide for the full walkthrough.

Common Debugging Prompts

These prompts cover the most common debugging scenarios:

This function returns undefined but it should return user data:

const user = await getUserById(userId);
console.log(user); // undefined

Trace through getUserById and its dependencies to find
where the data gets lost. Check the database query, any
transformations, and the return statements.

The checkout process fails silently. No error, but the order
doesn't get created.

Add logging to trace the flow through:
- CartController.checkout()
- OrderService.createOrder()
- PaymentService.processPayment()

Show me the log output so we can see where it stops.

Fix this error, but explain:
1. What caused it
2. Why your fix works
3. How I can prevent similar bugs

Error: Maximum call stack size exceeded
    at deepClone (src/utils/clone.js:5:12)
    at deepClone (src/utils/clone.js:8:16)
    at deepClone (src/utils/clone.js:8:16)
    ...

This endpoint worked yesterday but now returns 403:

GET /api/admin/reports

Nothing in the code changed. Compare the current auth middleware
with what's in git from 2 days ago. What's different that could
cause this?

When to Use Plan Mode for Debugging

Plan Mode is useful for complex debugging scenarios. Enter it by pressing Shift+Tab twice.

Use Plan Mode when:

• The bug touches multiple files or systems
• You do not understand the codebase well enough to know where to look
• The error message does not point to a clear source
• You want Claude to analyze the architecture before making changes

Use Normal Mode when:

• The error message clearly identifies the problem file and line
• It is a simple syntax error or typo
• You have debugged similar issues before
• You want Claude to just fix it quickly

Plan Mode Debugging Example

> [Plan Mode enabled]
> Users report that notifications arrive late, sometimes hours
> after the triggering event. Analyze the notification system
> and identify possible causes.

Claude: I'll analyze the notification system...

[Claude reads files]

I found the notification flow:
1. Event triggers in src/events/handlers.js
2. Queued via src/queue/notifications.js
3. Processed by src/workers/notification-worker.js
4. Sent via src/services/email.js and src/services/push.js

Potential delay points I found:

1. Queue polling interval: Worker checks every 60 seconds
   (src/workers/notification-worker.js:15)

2. Batch processing: Worker processes 100 notifications
   per batch, waits for all to complete before next batch

3. Rate limiting: Email service has 10/second limit, but
   no queue-side awareness of this

4. No priority system: Urgent notifications wait behind
   marketing emails

Recommended investigation order:
1. Check queue depth and processing times in logs
2. Verify worker is running and not crashing
3. Review rate limit handling
4. Consider adding priority queues

Should I check the logs for queue metrics first?

Debug Frontend Issues with Chrome Integration

Claude Code now integrates with the Claude in Chrome browser extension (beta), which is especially powerful for debugging frontend issues. With the extension connected, Claude can:

• Open your web app in Chrome and read browser console errors directly
• Inspect network requests and identify failed API calls
• Check DOM state and verify that elements render correctly
• Test interactions like button clicks and form submissions

This eliminates the need to manually copy console errors. Claude sees them in real-time and can trace frontend issues back to the source code. The Chrome integration is available to all paid plan users.

VS Code Checkpoints for Safe Debugging

If you use Claude Code inside VS Code (via the official extension), you get access to checkpoints. Checkpoints track every file edit Claude makes and let you rewind to any previous state. This is invaluable during debugging—if Claude's fix makes things worse, you can instantly roll back and try a different approach. Options include forking the conversation, rewinding code changes, or both.

Debugging Without Error Messages

Logic bugs and unexpected behavior often do not produce error messages. Here is how to debug them:

The discount code applies but the total doesn't change.

Expected: 20% off the subtotal
Actual: Full price charged

The discount code is "SAVE20" and it's marked as active
in the database. Walk through the checkout calculation
in @src/services/pricing.js

The "Export to CSV" button does nothing when clicked.
No error in console, no network request, nothing.

The button is in @src/components/DataTable.jsx
Check if the click handler is attached and trace what
should happen when it's clicked.

The monthly report shows $50,000 revenue but manual
calculation shows $62,000.

Audit the revenue calculation in @src/reports/monthly.js
Check:
- Are all order statuses included correctly?
- Is the date range filter working?
- Are refunds being double-counted?

Common Mistakes When Debugging

FAQ

Can Claude Code debug any programming language?

Claude can debug most popular languages including JavaScript, TypeScript, Python, Java, C#, Go, Ruby, PHP, Rust, and more. It understands language-specific errors and idioms.

What if Claude's fix doesn't work?

Give Claude the new error message or describe what is still broken. Debugging is iterative. Claude learns from each attempt and refines its approach.

Can Claude debug production issues?

Yes, if you give Claude access to logs and error reports. Paste production error messages, log snippets, and describe the conditions. Claude can analyze without needing direct production access.

How do I debug performance issues?

Describe the performance problem: "This query takes 30 seconds." Share the code and any profiling data. Claude can identify inefficient patterns, missing indexes, N+1 queries, and other performance bugs.

Should I use Claude Code or a traditional debugger?

Use both. Traditional debuggers let you step through code and inspect state in real-time. Claude Code helps you understand what you are seeing and suggests where to set breakpoints. They complement each other.

Can I pipe test output directly to Claude Code?

Yes. Run npm run test 2>&1 | claude -p "Fix these failing tests" to send test output directly to Claude for analysis. This works with any command—build errors, linting warnings, or runtime logs.

Can Claude debug frontend issues in the browser?

Yes. Claude Code's Chrome integration (beta) lets Claude read browser console errors, inspect network requests, and check DOM state directly. Install the Claude in Chrome extension and connect it to Claude Code.

Which Claude model is best for debugging?

Claude Opus 4.6 (the default) is best for complex multi-file debugging that requires deep reasoning. For quick error lookups, Claude may delegate exploration to its built-in Haiku 4.5 subagent, which is faster and keeps verbose search output out of your main conversation.

Related Guides

• How to Use Plan Mode — research-first debugging for complex bugs
• Claude Code Prompts and Examples — more prompt patterns
• Code Reviews with Claude Code — catch bugs before they ship
• Create Custom Agents — build a dedicated debugger agent
• What Is Claude Code? — the fundamentals
• Claude Code Tutorial for Beginners — start here if you are new