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Agent skill

Systematic Debugging

by sammcj in sammcj/agentic-coding

Applies a modified Fagan Inspection methodology to resolve persistent bugs and complex issues.

Apache-2.0Auto-check passedDevelopment

Install Systematic Debugging

skills CLI
$ npx skills add sammcj/agentic-coding --skill systematic-debugging -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install sammcj/agentic-coding systematic-debugging --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/sammcj/agentic-coding.git skills-src && mkdir -p .claude/skills && cp -r skills-src/Skills/systematic-debugging .claude/skills/systematic-debugging && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
systematic-debugging
GitHub stars
162
Token cost
~1.3k tokens
SKILL.md length
674 words
Files
1
Skills in repo
65
Repo updated
First seen
Licence
Apache-2.0

At a glance

Applies a modified Fagan Inspection methodology to resolve persistent bugs and complex issues.

  • Works in 4 steps: Initial Overview → Systematic Inspection → Root Cause Analysis → …
  • Debugging attempts have already failed and a methodical root-cause analysis warranting a Fagan inspection is needed
  • SKILL.md covers Process Overview, Important Guidelines, Final Output and When This Skill Should NOT Be…
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Systematic Debugging is an agent skill from sammcj/agentic-coding. Applies a modified Fagan Inspection methodology to resolve persistent bugs and complex issues. Use when several fix or debugging attempts have already failed and a methodical root-cause analysis warranting a Fagan inspection is needed. Do not use for simple troubleshooting.

Its SKILL.md is about 1.3k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Development, covering Debugging and Root cause analysis. The repository describes itself as: Agentic Coding Rules, Templates etc... The licence is Apache-2.0.

When your agent uses it

  • Debugging attempts have already failed and a methodical root-cause analysis warranting a Fagan inspection is needed
  • Simple troubleshooting

Example prompts

  • “Use the systematic-debugging skill to apply a modified Fagan Inspection methodology to resolve persistent bugs and complex issues”
  • “/systematic-debugging”

Workflow steps

4 steps, taken from the step headings in SKILL.md.

  1. Initial Overview
  2. Systematic Inspection
  3. Root Cause Analysis
  4. Solution & Verification

What it can do on your machine

Read from SKILL.md and the folder at commit 415ac71. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md.

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Systematic Debugging loads about 1.3k tokens when it runs. Until then it costs about 74 tokens; SKILL.md has 674 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~74
When it runs · the whole SKILL.md, loaded when a task matches
~1.3k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from sammcj/agentic-coding at commit 415ac71, republished under its Apache-2.0 licence (© sammcj). 674 words, ~1,273 tokens.

Download SKILL.mdSave it as .claude/skills/systematic-debugging/SKILL.md (or your agent's skills folder).
name
systematic-debugging
description
Applies a modified Fagan Inspection methodology to resolve persistent bugs and complex issues. Use when several fix or debugging attempts have already failed and a methodical root-cause analysis warranting a Fagan inspection is needed. Do not use for simple troubleshooting.

Systematic Debugging with Fagan Inspection

This skill applies a modified Fagan Inspection methodology for systematic problem resolution when facing complex problems or stubborn bugs that have resisted multiple fix attempts.

Process Overview

Create tasks for each of the four phases, then work them to completion, marking each done before starting the next.

Follow these four phases sequentially. Do not skip phases or attempt fixes before completing the inspection.

Phase 1: Initial Overview

Establish a clear understanding of the problem before analysis:

  • Explain the problem in plain language without technical jargon
  • State expected behaviour - what should happen
  • State actual behaviour - what is happening instead
  • Document symptoms - error messages, logs, observable failures
  • Context - when does it occur, how often, under what conditions
  • Prior fix attempts - list each attempt, what it changed, and why it failed; treat these as eliminated hypotheses that Phase 3 must account for

Output: A clear problem statement that anyone could understand.

Phase 2: Systematic Inspection

Perform a line-by-line walkthrough as the "Reader" role in Fagan Inspection. Identify defects without attempting to fix them yet - this is pure inspection.

Check against these defect categories:

  1. Logic Errors
  2. Boundary Conditions
  3. Error Handling
  4. Data Flow Issues
  5. Integration Points

Talk through the code step by step, as the Reader does in a Fagan inspection. For each section of code:

  • State what the code is intended to do
  • Identify any discrepancies between intent and implementation
  • Flag assumptions or unclear aspects
  • Use ultrathink to think deeper on complex sections

Output: A categorised list of identified defects with line numbers and specific descriptions.

Phase 3: Root Cause Analysis

After identifying issues, trace back to find the fundamental cause - not just symptoms.

Five Whys Technique:

  • Ask "why" repeatedly (at least 3-5 times) to get to the underlying issue
  • State each "why" explicitly in your analysis
  • Example:
    • Why did the API call fail? → Because the request was malformed
    • Why was it malformed? → Because the data wasn't serialised correctly
    • Why wasn't it serialised? → Because the serialiser expected a different type
    • Why did it expect a different type? → Because the schema was updated but code wasn't
    • Root cause: Schema versioning mismatch between services

Consider:

  • Environmental factors (configuration, dependencies, runtime environment)
  • Timing and concurrency (race conditions, async issues)
  • Hidden assumptions in the code or system design
  • Historical context (recent changes, migrations, updates)

State assumptions explicitly:

  • "I'm assuming X because..."
  • "This presumes that Y is always..."
  • Flag any assumptions that need verification

Output: A clear statement of the root cause, the chain of reasoning that led to it, and any assumptions that need validation.

Show full SKILL.md (247 more words)Show less
Phase 4: Solution & Verification

Now propose specific fixes for each identified issue.

For each proposed solution:

  1. Describe the fix - what code/configuration changes are needed
  2. Explain why it resolves the root cause - connect it back to Phase 3 analysis
  3. Consider side effects - what else might this change affect
  4. Define verification steps - how to confirm the fix works

Verification Planning:

  • Specific test cases that would have caught this bug
  • Manual verification steps
  • Monitoring or logging to add
  • Edge cases to validate

Use a sub-agent as a sounding board to provide critical feedback on your proposed solutions and verification plan.

Output: A summary of findings (key defects and root cause), a prioritised list of proposed fixes with rationale, and a verification plan for confirming the fixes work.

Important Guidelines

  • Complete each phase thoroughly before moving to the next
  • Flag unclear aspects rather than guessing - if something is uncertain, say so
  • Use available tools - read files, search code, run tests, check logs
  • Focus on systematic analysis over quick fixes
  • Validate flagged aspects - after completing all phases, revisit any unclear points and verify them with tools

Final Output

After completing all four phases, unless the user indicates otherwise, proceed to implement the proposed solutions.

When This Skill Should NOT Be Used

  • For simple, obvious bugs with clear fixes
  • When the first debugging attempt is still underway
  • For new features (this is for debugging existing code)
  • When the problem is clearly environmental (config, infrastructure) and doesn't require code inspection

© sammcj, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in Skills/systematic-debugging of sammcj/agentic-coding.

Open the folder on GitHubat commit 415ac71

Compare with similar skills

Systematic Debugging next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Systematic Debugging compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Systematic Debugging this skillsammcj/agentic-coding162—~1.3kAutomated safety check: PassApache-2.0
OpenLogi macOS Permissions TriageAprilNEA/OpenLogi23k—~2.5kAutomated safety check: NotesApache-2.0
Bug Finder for daisyUIsaadeghi/daisyui43k—~2.3kAutomated safety check: PassMIT
Root Cause Debugginggarrytan/gstack136k—~1.4kAutomated safety check: PassMIT
Graph-Based Bug Tracingtirth8205/code-review-graph32k1 repos~287Automated safety check: PassMIT
Systematic DebuggingChrisWiles/claude-code-showcase6.1k3 repos~1.2kAutomated safety check: PassNone

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Categories

Questions about Systematic Debugging

What does Systematic Debugging do?

Applies a modified Fagan Inspection methodology to resolve persistent bugs and complex issues. Systematic Debugging is an agent skill from sammcj/agentic-coding. Applies a modified Fagan Inspection methodology to resolve persistent bugs and complex issues.

When should I use Systematic Debugging?

Systematic Debugging fits situations like: debugging attempts have already failed and a methodical root-cause analysis warranting a Fagan inspection is needed; simple troubleshooting.

How do I install Systematic Debugging in Claude Code?

Run `npx skills add sammcj/agentic-coding --skill systematic-debugging -a claude-code`. Or copy the skill folder (Skills/systematic-debugging in sammcj/agentic-coding) into .claude/skills/systematic-debugging in your project. Claude Code loads it when a task matches its description.

How do I install Systematic Debugging in Codex?

Run `npx skills add sammcj/agentic-coding --skill systematic-debugging -a codex`. Or copy the skill folder (Skills/systematic-debugging in sammcj/agentic-coding) into .agents/skills/systematic-debugging in your project. Codex loads it when a task matches its description.

Can I use Systematic Debugging in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add sammcj/agentic-coding --skill systematic-debugging -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/systematic-debugging, .gemini/skills/systematic-debugging, .github/skills/systematic-debugging and .opencode/skills/systematic-debugging in your project.

What does Systematic Debugging need to run?

SKILL.md names no scripts, command-line tools or credentials: Systematic Debugging is instructions for the agent only.

Does Systematic Debugging access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Systematic Debugging safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Systematic Debugging use?

Systematic Debugging is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Systematic Debugging use?

About 1.3k tokens (SKILL.md is roughly 5.1k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Systematic Debugging?

Skills that share tags, products or a category with Systematic Debugging: OpenLogi macOS Permissions Triage (AprilNEA/OpenLogi, 23k stars), Bug Finder for daisyUI (saadeghi/daisyui, 43k stars), Root Cause Debugging (garrytan/gstack, 136k stars) and Graph-Based Bug Tracing (tirth8205/code-review-graph, 32k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Systematic Debugging?

sammcj (a GitHub user) maintains it in sammcj/agentic-coding, which has 162 GitHub stars. The repository holds 65 skills in this directory. The repository was last updated on October 5, 2026.

Source: sammcj/agentic-coding on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.