systematic-debugging

systematic-debugging is a skill for Claude Code, Codex from marcoguillermaz/Tierward. It costs 31 tokens per session (876 once invoked), scanned A, original, MIT.

A debugging process that requires investigating the cause of a bug, failed test, unexpected result, or build error before proposing a fix.

In plain words
What is it for?
Use it to reproduce an issue, read its full evidence, check recent changes, and trace failures across connected parts of a system.
Why use it?
It reduces guesswork and helps prevent quick patches that hide the real problem or create new bugs.

Skill for Claude CodeCodex

Part of the tierward plugin — 29 skills, 1 command, 1 hook, 1 MCP server shipped together

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 skills/marcoguillermaz/tierward/systematic-debugging
Any agent
npx skills add marcoguillermaz/Tierward --skill systematic-debugging
Clone the repo
git clone --depth 1 https://github.com/marcoguillermaz/Tierward

Made for: Claude Code, Codex.

Or install tierward, the plugin that ships this one along with the rest of its 29 skills, 1 command, 1 hook, 1 MCP server.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for systematic-debugging

README.md
[![agentmods](https://agentmods.dev/badge/skills/marcoguillermaz/tierward/systematic-debugging.svg)](https://agentmods.dev/skills/marcoguillermaz/tierward/systematic-debugging)
Your own site
<a href="https://agentmods.dev/skills/marcoguillermaz/tierward/systematic-debugging"><img src="https://agentmods.dev/badge/skills/marcoguillermaz/tierward/systematic-debugging.svg" alt="Measured on agentmods" height="20"></a>
Per session 31 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 876 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. 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 $0.00031 $0.00876
Opus 5 $0.00015 $0.00438
Sonnet 5 $0.00006 $0.00175
Haiku 4.5 $0.00003 $0.00088

Measured 5d ago against content hash 38ce85056921, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

systematic-debugging scanned grade A with 0 findings 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 5d 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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

packages/cli/templates/tier-l/.claude/skills/systematic-debugging/SKILL.md · 84 lines

How it starts

The opening of the file, as written. The whole thing — 84 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Systematic Debugging

Random fixes waste time and introduce new bugs. Quick patches mask root causes.

The Iron Law: complete Phase 1 before proposing any fix. Skipping Phase 1 is not using this skill.

When to use

Any technical issue: test failures, runtime bugs, unexpected output, build errors, integration failures, performance regressions.

Use especially when:

  • "One quick fix" seems obvious — that intuition is untested
  • You have already tried one fix and it did not work
  • The issue appears in a multi-component system (CI → build → sign, API → service → DB)

Phase 1 — Reproduce & read evidence

Before any fix:

  1. Read the error message fully. Stack traces, file paths, line numbers, error codes. Do not paraphrase — the text often contains the direct cause.

  2. Reproduce consistently. List exact steps that trigger the issue. If not reproducible: add logging or assertions, gather more data, do not guess.

  3. Check recent changes. What changed that could cause this? Git diff, new dependencies, config changes, environment differences.

  4. In multi-component systems: add a log or assertion at each component boundary. Run once to identify which layer fails, then investigate that layer specifically.

Phase 2 — Pattern analysis

  1. Find working code similar to what is broken.
  2. List every difference between working and broken. Do not assume "that can't matter."
  3. Identify what the broken code depends on: config, state, environment, calling conventions.

Phase 3 — Hypothesize

Write the hypothesis before touching any code:

"The root cause is [X] because [Y]. Prediction: if X is true, then [Z] should also be observable."

Verify the prediction against Phase 1 evidence before proceeding.

* STOP — hypothesis written and verified against evidence. Wait for confirmation before Phase 4. *

Phase 4 — Fix the root cause

  1. Create a repro case before writing any fix — failing test, minimal script, or manual reproduction recipe. Must exist.

Read the full file on GitHub · 84 lines

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. 5d ago First seen · 84 lines · 31 tokens per session scan A 38ce85056921

Subscribe to this mod's changes

systematic-debugging is a skill published in the GitHub repository marcoguillermaz/Tierward (4 stars, last pushed yesterday), licensed MIT. It adds 31 tokens to every session and 876 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.