Java Debug Agent

December 11, 2025 · View on GitHub

The Java Debug Agent is an AI-powered debugging assistant that integrates with GitHub Copilot Chat to help you debug Java applications using natural language.

Overview

Instead of manually setting breakpoints and inspecting variables, you can simply describe your debugging task in natural language. The agent will:

  1. Analyze your code to form hypotheses
  2. Set targeted breakpoints
  3. Inspect variables and evaluate expressions
  4. Find the root cause of bugs

Requirements

Getting Started

1. Open Copilot Chat

Press Ctrl+Shift+I (Windows/Linux) or Cmd+Shift+I (macOS) to open Copilot Chat.

2. Switch to JavaDebug Agent Mode

In the Copilot Chat panel, click on the agent selector (usually shows "Copilot" or current agent name) and select JavaDebug from the dropdown list.

Select Agent

3. Enter Your Debugging Request

Once in JavaDebug mode, simply type your debugging request:

Why am I getting a NullPointerException in OrderService?

Invoke Agent

4. Let the Agent Work

The agent will:

  • Read relevant code files
  • Form a hypothesis about the bug
  • Set breakpoints at strategic locations
  • Start or attach to a debug session
  • Inspect variables to verify the hypothesis
  • Report the root cause

Agent Working

Example Usage

Debug a NullPointerException

I'm getting NPE when calling userService.getUser()

The agent will:

  1. Read UserService.java
  2. Hypothesize which variable might be null
  3. Set a breakpoint before the NPE
  4. Check variable values
  5. Report: "The user variable is null because findById() returns null when ID doesn't exist"

Debug Wrong Calculation Result

The calculateTotal() method returns wrong value

Debug with Specific Input

Debug processOrder with orderId=456

Debug Multi-threaded Issues

I suspect a race condition in the worker threads

Agent Capabilities

CapabilityDescription
Start Debug SessionLaunch or attach to Java applications
Set BreakpointsSet conditional or unconditional breakpoints
Inspect VariablesView local variables, fields, and objects
Evaluate ExpressionsExecute Java expressions in debug context
Step Through CodeStep over, step into, step out
Multi-thread SupportDebug concurrent applications
Stack Trace AnalysisView and navigate call stacks

How It Works

The agent uses hypothesis-driven debugging:

┌─────────────────────────────────────────┐
│  1. STATIC ANALYSIS                     │
│     Read code, understand the problem   │
└─────────────────┬───────────────────────┘
                  ↓
┌─────────────────────────────────────────┐
│  2. FORM HYPOTHESIS                     │
│     "Variable X is null at line Y"      │
└─────────────────┬───────────────────────┘
                  ↓
┌─────────────────────────────────────────┐
│  3. SET BREAKPOINT                      │
│     At the location to verify           │
└─────────────────┬───────────────────────┘
                  ↓
┌─────────────────────────────────────────┐
│  4. VERIFY                              │
│     Check if hypothesis is correct      │
│     ├─ YES → Report root cause          │
│     └─ NO  → Form new hypothesis        │
└─────────────────────────────────────────┘

Tips for Best Results

Stay in Agent Mode

Make sure you're in JavaDebug agent mode (check the agent selector in Chat panel). If you switch back to default Copilot mode, the debugging tools won't be available.

Be Specific

✅ Good: "Why does getUserById return null when id=123?"
❌ Vague: "Something is wrong"

Mention the Error

✅ Good: "Getting ArrayIndexOutOfBoundsException in processItems()"
❌ Vague: "Debug processItems"

Provide Context

✅ Good: "The order total is \$0 instead of \$150 for order 456"
❌ Vague: "Wrong calculation"

Troubleshooting

Agent Can't Find the File

Make sure the Java project is properly loaded. Check that:

  • The Java extension is activated (look for Java icon in status bar)
  • The project is imported (check Java Projects view)

Debug Session Won't Start

Ensure:

  • Your project compiles successfully
  • No other debug session is running
  • The main class can be found

Breakpoint Not Hit

The agent will tell you to trigger the scenario. You need to:

  1. Run the part of your application that executes the code
  2. The breakpoint will be hit when the code path is executed

Limitations

  • Requires an active Java project with proper configuration
  • Cannot debug remote applications without proper attach configuration
  • Performance may vary with large codebases

Feedback

If you encounter issues or have suggestions, please:

  • File an issue on GitHub
  • Include the agent's response and your debugging request

See Also