java-debug-inspection

Testing & Quality

Use when inspecting a Java program that is already being debugged — read local variables, walk the call stack, list threads, evaluate expressions, step in/over/out, continue execution, or set / remove breakpoints in an active Java debug session. NOT for starting, launching, or stopping a debug session — use `java-launch-troubleshooting` for that.

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Source SKILL.md: https://github.com/microsoft/vscode-java-debug/blob/HEAD/resources/skills/java-debug-inspection/SKILL.md

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Java Debug Inspection

Use this skill when a Java debug session is already active (the user has launched the program with debug_java_application or via the VS Code Run/Debug UI) and they want to observe or steer the running program. Typical user phrases:

"what's the value of user.id right now?", "show me the local variables"
"evaluate list.size()", "what does service.findById(42) return at this frame?"
"show the stack trace", "what threads are running?", "go up one frame"
"step in", "step over", "step out", "continue", "resume"
"set a breakpoint at OrderService.placeOrder", "remove the breakpoint on line 42"

If no debug session is active, this skill should not be used — load java-launch-troubleshooting first to start one.

Tools

These language model tools are contributed by the Debugger for Java extension and are deferred. Activate them with tool_search_tool_regex using pattern java_breakpoint|debug before first use.

Tool	Purpose
`get_debug_variables`	Read local variables, fields, and watched expressions in the current frame.
`get_debug_stack_trace`	List call-stack frames for the focused (or specified) thread.
`get_debug_threads`	List all threads in the session with state (running, stopped, terminated).
`evaluate_debug_expression`	Evaluate an arbitrary Java expression in the context of the focused frame.
`debug_step_operation`	Step in, step over, step out, or continue. Requires the program to be paused.
`set_java_breakpoint`	Set a line / method / exception breakpoint. Works at any time during the session.
`remove_java_breakpoints`	Remove one or more breakpoints by ID or location.

Preferred Workflow

Confirm session state. If the user asks to step or evaluate an expression, the program must be paused (typically at a breakpoint). If unsure, call get_debug_session_info from java-launch-troubleshooting to check, or list threads with get_debug_threads.
Inspect first, then act. For "what's the value of X" — call get_debug_variables or evaluate_debug_expression. Do not guess from source code.
Step / continue. For "step over" / "step in" / "step out" / "continue", call debug_step_operation with the matching action. After each step, re-read variables or stack as needed.
Breakpoints. For "set a breakpoint at …", call set_java_breakpoint with the file URI + line, or fully qualified method signature, or exception class. For "remove the breakpoint at …", call remove_java_breakpoints.
Report precisely. Quote the exact value or stack frame returned by the tool — do not paraphrase.

Common Pitfalls

Symptom	Likely cause	Fix
`debug_step_operation` returns "thread is not paused"	The program is running, not stopped at a breakpoint	Ask the user to add a breakpoint first, or wait for the next stop event
`evaluate_debug_expression` returns `<no active frame>`	No focused stack frame, often because the session just resumed	Re-call `get_debug_stack_trace` to refocus a frame
`get_debug_variables` returns empty for a parameter	Compilation without `-g` (no local variable table)	Inform user; offer to inspect via `evaluate_debug_expression` instead
Step in jumps into JDK internals	Default step filters disabled	Suggest enabling `java.debug.settings.stepping.skipClasses`

When NOT to Use This Skill

The user wants to start a Java program (no session yet) → use java-launch-troubleshooting
The user wants to stop the session → use stop_debug_session from java-launch-troubleshooting
The program is a non-Java language → do not load this skill
The user is editing source code without an active debug session → do nothing

Fallback

If a tool returns "Java Language Server not ready" or repeats the same error twice, report the raw error to the user and stop calling debug tools for the current turn. Do not retry more than twice.