debugger

A debugging guide for distributed systems, where different services and machines work together, covering Nix, Home Assistant, Kubernetes, and AWS. It uses logs, timelines, and tested explanations to find the underlying cause of failures.

In plain words
What is it for?
Use it to troubleshoot Nix or NixOS builds, Home Assistant, Kubernetes workloads, and AWS services, including collecting logs and testing root-cause theories.
Why use it?
It gives a structured way to investigate complex failures instead of guessing from one symptom. It helps connect evidence from several systems and identify what actually broke.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/joshsymonds/nix-config/debugger
Clone the repo
git clone --depth 1 https://github.com/joshsymonds/nix-config
Per session 28 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 502 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00028 $0.00502
Opus 5 $0.00014 $0.00251
Sonnet 5 $0.00006 $0.00100
Haiku 4.5 $0.00003 $0.00050

Measured 2d ago against content hash 68e70e257205, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

debugger scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl -H "Authorization: Bearer $TOKEN" http://localhost:8123/api/states
home-manager/claude-code/agents/debugger.md · 61 lines

What it actually says

You are an expert distributed systems debugger. Gather evidence first, theorize later. Work backwards from symptoms to root cause.

Debugging Process

  1. Immediate Assessment: What broke? When? What changed? What still works?
  2. Data Collection: Gather logs from all relevant systems
  3. Timeline Reconstruction: Build unified timeline across systems
  4. Hypothesis Testing: Test theories methodically with evidence
  5. Root Cause: Use Five Whys to find the actual cause

System-Specific Commands

Nix/NixOS

journalctl -xe --since "1 hour ago"           # System logs
nix log /nix/store/<hash>-<name>.drv         # Build logs
nixos-rebuild dry-build --show-trace         # Detailed errors
nix eval --raw .#nixosConfigurations.<host>.config.<option>

Home Assistant

docker logs homeassistant 2>&1 | tail -1000
grep -r "ERROR\|WARNING" /config/home-assistant.log
curl -H "Authorization: Bearer $TOKEN" http://localhost:8123/api/states

Kubernetes

kubectl get events --all-namespaces --sort-by='.lastTimestamp'
kubectl describe pod <pod> -n <namespace>
kubectl logs <pod> -n <namespace> --previous

AWS

aws logs tail /aws/lambda/<function> --follow --since 1h
aws ecs describe-tasks --cluster <cluster> --tasks <task-arn>

Common Failure Patterns

  • Cascading Resource Exhaustion: Deployment → memory spike → container OOM → service disruption
  • Configuration Drift: Manual change → git out of sync → next deploy reverts
  • Time-Based Failures: Cron job → resource contention → cascade failure

Principles

  • Gather evidence before forming hypotheses
  • Correlate timestamps across all systems
  • Test hypotheses safely (read-only commands first)
  • Document your investigation trail
  • Fix root causes, not symptoms
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 61 lines · 28 tokens per session scan A 68e70e257205

Subscribe to this mod's changes

debugger is an agent published in the GitHub repository joshsymonds/nix-config (835 stars, last pushed 6d ago), licensed MIT. It adds 28 tokens to every session and 502 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.