MoAI Essentials Debug v2.1

Skill Metadata

What it does

Comprehensive debugging support across all 23 MoAI-ADK languages with:

• Language-specific debugger integration
• Stack trace analysis and error pattern detection
• Container and Kubernetes debugging
• Distributed tracing with OpenTelemetry
• Cloud debugger integration (AWS X-Ray, GCP Cloud Debugger)
• Performance profiling with Prometheus

When to use

• Runtime errors, exceptions, crashes
• Stack trace analysis requests
• "Why is this failing?", "Debug this error"
• Container/K8s debugging scenarios
• Distributed system tracing
• Performance bottleneck investigation
• Automatically invoked via debug-helper sub-agent

Quick Reference: Debugger by Language

Systems Programming

• C/C++: gdb 14.x, lldb 17.x, AddressSanitizer
• Rust: rust-lldb, rust-gdb, RUST_BACKTRACE=1
• Go: Delve 1.22.x, goroutine debugging

JVM Ecosystem

• Java: jdb, IntelliJ IDEA, Remote JDWP
• Kotlin: IntelliJ Kotlin Debugger, Coroutines debugger
• Scala: IntelliJ Scala Plugin, sbt debug mode
• Clojure: CIDER, Cursive, REPL-based debugging

Scripting Languages

• Python: pdb, debugpy 1.8.0, pudb (TUI)
• Ruby: debug gem (built-in), byebug, pry-byebug
• PHP: Xdebug 3.3.x, phpdbg
• Lua: ZeroBrane Studio, MobDebug
• Shell: bash -x, set -x toggle

Web & Mobile

• JavaScript: Chrome DevTools, node --inspect
• TypeScript: Chrome DevTools with source maps, VS Code debugger
• Dart/Flutter: Flutter DevTools, hot reload
• Swift: LLDB (Xcode), Instruments profiling

Functional & Concurrency

• Haskell: GHCi debugger, Debug.Trace
• Elixir: IEx debugger, :observer.start()
• Julia: Debugger.jl, Infiltrator.jl
• R: browser(), debug(), RStudio debugger

Enterprise & Data

• C#: Visual Studio Debugger, Rider, vsdbg
• SQL: EXPLAIN ANALYZE, pg_stat_statements

Complete debugger matrix with CLI commands: See reference.md

Debugging Workflow (6-Step Process)

1. Reproduce

• Minimal reproducible example (MRE)
• Consistent reproduction steps
• Document environment (OS, language version, dependencies)

2. Isolate

• Binary search the code (comment out sections)
• Check recent changes (git diff, git log)
• Verify input data and edge cases

3. Investigate

• Read stack trace from bottom (entry point) to top (error site)
• Add logging at key decision points
• Use debugger breakpoints before error location
• Check variable state in debugger

4. Hypothesize

• Form theory about root cause
• Identify 2-3 most likely culprits
• Design experiment to test hypothesis

5. Fix

• Implement minimal fix first
• Add regression test (RED → GREEN)
• Refactor if needed (REFACTOR stage)
• Update documentation

6. Verify

• Run full test suite
• Test edge cases explicitly
• Verify fix in production-like environment
• Monitor for recurrence

Common Error Patterns by Language Category

Memory Safety

• C/C++: Buffer overflow, use-after-free, memory leaks
  • Tools: Valgrind, AddressSanitizer (-fsanitize=address)
• Rust: Ownership violations (prevented at compile time)
• Go: Goroutine leaks, improper channel usage

Null/Nil Handling

• Java: NullPointerException → Use Optional<T>
• Kotlin: NullPointerException → Leverage null safety (?.)
• TypeScript: undefined access → Optional chaining (?.)
• Go: Nil pointer → Early nil checks
• Rust: Option<T> unwrap → Pattern matching

Type Errors

• Python: TypeError, AttributeError → Type hints + mypy
• JavaScript: Type coercion bugs → Use TypeScript
• Ruby: NoMethodError → Duck typing checks

Concurrency Issues

• Go: Data races → go build -race, proper channel usage
• Java: ConcurrentModificationException → Use concurrent collections
• Rust: Data races (prevented by borrow checker)
• Python: GIL limitations → Use multiprocessing for CPU-bound tasks

Async/Await Pitfalls

• Python: RuntimeError: Event loop is closed → Proper asyncio usage
• JavaScript: Unhandled promise rejections → Always catch async errors
• Rust: Send/Sync trait violations → Understand thread safety

Detailed error pattern analysis: See examples.md

Container & Kubernetes Debugging

Docker Debugging

# Attach to running container
docker exec -it <container> /bin/sh

# Debug with debugger ports exposed
docker run -p 5005:5005 -e JAVA_TOOL_OPTIONS='-agentlib:jdwp=...' myapp

# Python remote debugging
docker run -p 5678:5678 -e DEBUGPY_ENABLE=true myapp

Kubernetes Debugging

# Port-forward debugger port
kubectl port-forward pod/myapp-pod 5005:5005

# Exec into pod
kubectl exec -it myapp-pod -- /bin/bash

# Debug with ephemeral container (K8s 1.23+)
kubectl debug -it myapp-pod --image=busybox --target=myapp

Complete container debugging guide: See reference.md

Distributed Tracing

OpenTelemetry 1.24.0+

• Python: opentelemetry-api, opentelemetry-sdk
• TypeScript: @opentelemetry/sdk-trace-node
• Exporters: Jaeger, Zipkin, OTLP

Prometheus 2.48.x Integration

• Metrics: Counter, Gauge, Histogram, Summary
• Python: prometheus-client 0.19.0
• Go: prometheus/client_golang

Cloud Debuggers

• AWS X-Ray: aws-xray-sdk, auto-instrumentation
• GCP Cloud Debugger: googleclouddebugger Python package

Complete distributed tracing setup: See reference.md

Stack Trace Analysis Quick Guide

Reading Stack Traces

Direction: Bottom (entry point) → Top (error site)

Key information:

• 📍 Location: File and line number
• 🔍 Context: Function name and arguments
• 💡 Error type: Exception class or error message

Analysis Pattern

1. Identify error type: What exception/error?
2. Locate error site: Top of stack trace
3. Trace execution path: Follow stack from bottom
4. Identify root cause: Where did bad data/state originate?
5. Suggest fix: 1-3 actionable options

Language-specific stack trace examples: See examples.md

Performance Profiling Integration

CPU Profiling

• Python: cProfile, py-spy (production-safe)
• Go: pprof, go test -cpuprofile
• Rust: flamegraph crate
• Java: Java Flight Recorder (JFR)

Memory Profiling

• Python: memory_profiler, tracemalloc
• Go: pprof memory profiling
• C/C++: Valgrind massif
• Rust: heaptrack

Complete profiling guide: See reference.md

Inputs

• Stack traces, error messages, logs
• Code context (relevant files)
• Environment information (versions, config)
• Reproduction steps

Outputs

• Root cause analysis with evidence
• Actionable fix suggestions (1-3 options)
• Debugging checklist tailored to error type
• Code snippets demonstrating fix

Failure Modes

• Insufficient stack trace or log information
• Unable to reproduce error locally
• Complex distributed system failures requiring multi-service tracing
• Race conditions or timing-dependent bugs

Dependencies

• Works with: tdd-implementer, debug-helper, quality-gate
• Requires: Language-specific debugger tools installed
• Optional: OpenTelemetry, Prometheus, cloud debugger SDKs

Related Skills

• moai-essentials-refactor (clean up code after debugging)
• moai-essentials-perf (performance bottleneck investigation)
• moai-alfred-debugger-pro (advanced debugging strategies)
• moai-foundation-trust (ensure debugging doesn't skip tests)

Best Practices

• Always create regression test after fixing bug (TDD cycle)
• Log debugging insights in code comments with @TAG references
• Use language-appropriate debugger (don't force Python workflow on Go)
• Enable source maps for compiled/transpiled languages
• Set up distributed tracing early in microservices projects
• Use production-safe profilers (py-spy, async-profiler) in live systems
• Document reproduction steps in issue tracker or SPEC HISTORY

For complete 23-language debugger matrix: reference.md
For language-specific debugging examples: examples.md

End of Skill | Refactored 2025-10-27