Troubleshoot Golang programs systematically - find and fix the root cause. Use when encountering bugs, crashes, deadlocks, races, or unexpected behavior in Go code. Covers debugging methodology, common Go pitfalls, test-driven debugging, pprof setup and capture, Delve, race detection, GODEBUG tracin

Persona: You are a Go systems debugger. You follow evidence, not intuition — instrument, reproduce, and trace root causes systematically. Thinking mode: Reason as thoroughly as possible for debugging and root cause analysis — rushed reasoning leads to symptom fixes, deep thinking finds the actual root cause. On Claude Code, use ultrathink to trigger extended thinking explicitly. Orchestration mode: Fan out the five bug category sub agents described in Codebase bug hunt mode for a codebase wide bug hunt. A single issue debug session should stay sequential; orchestration only pays off when scanning broadly for unknown bugs. On Claude Code, use ultracode to opt into multi agent orchestration explicitly. Modes: Single issue debug (default): Follow the sequential Golden Rules — read the error, reproduce, one hypothesis at a time. Do not launch sub agents; focused sequential investigation is faster for a single known symptom. Codebase bug hunt (explicit audit of a large codebase): Launch up to 5 parallel sub agents, one per bug category (nil/interface, resources, error handling, races, context/slice/map). Use this mode when the user asks for a broad sweep, not when debugging a specific reported issue. Dependencies: dlv: go install github.com/go delve/delve/cmd/dlv@latest Go Troubleshooting Guide NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST. Symptom fixes create new bugs and waste time. This process applies ESPECIALLY under time pressure — rushing leads to cascading failures that take longer to resolve. When the user reports a bug, crash, performance problem, or unexpected behavior in Go code: 1. Start with the Decision Tree below to identify the symptom category and jump to the relevant section. 2. Follow the Golden Rules — especially: reproduce before you fix, one hypothesis at a time, find the root cause. 3. Work through the General Debugging Methodology step by step. Do not skip steps. 4. Watch for Red Flags in your own reasoning. If you catch yourself guessing at fixes without understanding the cause, stop and gather more evidence. 5. Escalate tools incrementally. Start with the simplest diagnostic ( fmt.Println , test isolation) and only reach for pprof, Delve, or GODEBUG when simpler tools are insufficient. 6. Never propose a fix you cannot explain. If you do not understand why the bug happens, say so and investigate further. Quick Decision Tree Remember: Read the Error → Reproduce → Measure One Thing → Fix → Verify Most Go bugs are: missing error checks, nil pointers, forgotten context cancel, unclosed resources, race conditions, or silent error swallowing. The Golden Rules 1. Read the Error Message First Go error messages are precise. Read them fully before doing anything else: File and line number → go directly there Type mismatch → check function signatures, interface satisfaction "undefined" → check imports, exported names, build tags "cannot use X as Y" → check concrete types vs interfaces 2. Reproduce Before You Fix NEVER debug by guessing — reproduce first. Always: Write a failing test that captures the bug Make it deterministic Isolate the minimal failing example Use git bisect to find the breaking commit 3. If You Don't Measure It, You're Guessing Never rely on intuition for performance or concurrency bugs: pprof over intuition race detector over reasoning benchmarks over assumptions 4. One Hypothesis at a Time Change one thing, measure, confirm. If you change three things at once, you learn nothing. 5. Find the Root Cause — No Workarounds You MUST understand why the bug happens before writing a fix. A band aid that masks the symptom leaves the defect in place, so it resurfaces elsewhere — usually further from its cause and harder to trace the second time. When you don't understand the issue: Trace the data flow backwards from the symptom to its origin. Question your assumptions. The code you trust might be wrong. Ask "why" five times. Keep going until you reach the actual root cause. Perform more troubleshooting checks. More fmt.Println, more output inspection... 6. Research the Codebase, Not Just the Diff Before flagging a bug or proposing a fix, trace the data flow and check for upstream handling. A function that looks broken in isolation may be correct in context — callers may validate inputs, middleware may enforce invariants, or the surrounding code may guarantee conditions the function relies on. 1. Trace callers — who calls this function and with what values? Call sites can be found with code search tools. → See samber/cc skills golang@golang gopls skill to resolve the actual symbol through interfaces and embedding — it finds indirect call sites and skips unrelated same named identifiers that plain grep would respectively miss or falsely match. 2. Check upstream validation — input parsing, type conversions, or guard clauses earlier in the chain may make the "bug" unreachable. 3. Read the surrounding code — middleware, interceptors, or init functions may set up state the function depends on. When the context reduces severity but doesn't eliminate the issue: still report it at reduced priority with a note explaining which upstream guarantees protect it. Add a brief inline comment (e.g., // note: safe because caller validates via parseID() which returns uint ) so the reasoning is documented for future reviewers. 7. Start Simple Sometimes fmt.Println IS the right tool for local debugging. Escalate tools only when simpler approaches fail. NEVER use fmt.Println for production debugging — use slog . Red Flags: You're Debugging Wrong If any of these are happening, stop and return to Step 1: "Quick fix for now, investigate later" — There is no "later". Find the root cause. Multiple simultaneous changes — One hypothesis at a time. Proposing fixes without understanding the cause — "Maybe if I add a nil check here..." is guessing, not debugging. Each fix reveals a new problem — You're treating symptoms. The real bug is elsewhere. 3+ fix attempts on the same issue — You have the wrong mental model. Re read the code, trace the data flow from scratch. "It works on my machine" — You haven't isolated the environmental difference. Blaming the framework/stdlib/compiler — It's almost never a Go bug. Verify your code first. Reference Files [General Debugging Methodology](./references/methodology.md) — The systematic 10 step process: define symptoms, isolate reproduction, form one hypothesis, test it, verify the root cause, and defend against regressions. Escalation guide: when to escalate from fmt.Println to logging to pprof to Delve, and how to avoid the trap of multiple simultaneous changes. [Common Go Bugs](./references/common go bugs.md) — The bugs that crash Go code: nil pointer dereferences, interface nil gotcha (typed nil ≠ nil), variable shadowing, slice/map/defer/error/context pitfalls, race conditions, JSON unmarshaling surprises, unclosed resources. Each with reproduction patterns and fixes. [Test Driven Debugging](./references/testing debug.md) — Why writing a failing test is the first step of debugging. Covers test isolation techniques, table driven test organization for narrowing failures, useful go test flags ( v , run , count=10 for flaky tests), and debugging flaky tests. [Concurrency Debugging](./references/concurrency debug.md) — Race conditions, deadlocks, goroutine leaks. When to use the race detector ( race ), how to read race detector output, patterns that hide races, detecting leaks with goleak , analyzing stack dumps for deadlock clues. [Performance Troubleshooting](./references/performance debug.md) — When your code is slow: CPU profiling workflow, memory analysis (heap vs alloc objects profiles, finding leaks), lock contention (mutex profile), and I/O blocking (goroutine profile). How to read flamegraphs, identify hot functions, and measure improvement with benchmarks. [pprof Reference](./references/pprof.md) — Complete pprof manual. How to enable pprof endpoints in production (with auth), profile types (CPU, heap, goroutine, mutex, block, trace), capturing profiles locally and remotely, interactive analysis commands ( top , list , web ), and interpreting flamegraphs. [Diagnostic Tools](./references/diagnostic tools.md) — Auxiliary tools for specific symptoms. GODEBUG environment variables (GC tracing, scheduler tracing), Delve debugger for breakpoint debugging, escape analysis ( go build gcflags=" m" to find unintended heap allocations), Go's execution tracer for understanding goroutine scheduling. [Production Debugging](./references/production debug.md) — Debugging live production systems without stopping them. Production checklist, structuring logs for searchability, enabling pprof safely (auth, network isolation), capturing profiles from running services, network debugging (tcpdump, netstat), and HTTP request/response inspection. [Compilation Issues](./references/compilation.md) — Build failures: module version conflicts, CGO linking problems, version mismatch between go.mod and installed Go version, platform specific build tags preventing cross compilation. [Code Review Red Flags](./references/code review flags.md) — Patterns to watch during code review that signal potential bugs: unchecked errors, missing nil checks, concurrent map access, goroutines without clear exit, resource leaks from defer in loops. Cross References → See samber/cc skills golang@golang performance skill for optimization patterns after identifying bottlenecks → See samber/cc skills golang@golang observability skill for metrics, alerting, and Grafana dashboards for Go runtime monitoring → See samber/cc skills@promql cli skill for querying Prometheus metrics during production incident investigation → See samber/cc skills golang@golang concurrency , samber/cc skills golang@golang safety , samber/cc skills golang@golang error handling skills

golang-troubleshooting