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debug-mantra — Claude Code skill: what it does, how to install

Sets a debugging sequence from reproducing a failure through testing hypotheses and recording experiments. Use it for errors, logs, and stack traces.

Install into Claude Code · Skills CLI (Vercel) All methods and platforms ↓ 
npx skills add thananon/9arm-skills --skill debug-mantra -a claude-code
Open on GitHub

What debug-mantra does

The skill opens a debugging session with a fixed mantra block, then follows four stages in sequence. It first requires a reproducible case, then narrows the failure path, tests candidate causes, and checks each result against the record of earlier runs.

It starts failure-path work with a debugger. When that cannot be used, it traces the source path and changes one influencing condition at a time, including configuration, environment variables, flags, input shape, timing, and concurrency. Code instrumentation with identifiable log markers comes later.

With no reproduction, the skill does not speculate. It asks for environment access, captured artifacts, or permission to add instrumentation, so having one of these ready matters before investigating. It also tests the simplest disproof before accepting a hypothesis and keeps an experiment ledger throughout the session.

What it helps with

  • build a reproducible failing case
  • locate the code path that fails
  • disprove a suspected root cause
  • record changes and outcomes for each run
  • compare a new theory with prior observations

Example prompts for the agent

  • `/debug-mantra` Investigate this application error.
  • `/debug-mantra` Diagnose the failure from this error log.
  • `/debug-mantra` Find why this test is failing.

How to install debug-mantra

1Skills CLI (Vercel)

npx skills add thananon/9arm-skills --skill debug-mantra -a claude-code

2Manually: put the files in place

~/.claude/skills/debug-mantra/SKILL.md

Copy the whole skill folder; for one project use .claude/skills/debug-mantra/

From the same set3

The whole set →
scrutinize thananon An outsider-perspective review skill for plans, pull requests, and diffs. It challenges intent first, traces execution paths beyond the diff, and flags structural flaws. Claude Code CX Codex Cursor +1 5,200installs post-mortem thananon Skill writes an engineering post-mortem after debugging: root cause with code identifiers, symptom, mechanism, the fix, and why it slipped through. Use after validation, before closing the ticket. Claude Code CX Codex Cursor +1 4,700installs

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Questions about debug-mantra

How do I install debug-mantra in Claude Code?

Run npx skills add thananon/9arm-skills --skill debug-mantra -a claude-code, then run npx skills add thananon/9arm-skills --skill debug-mantra -a claude-code again. The skill file is placed at ~/.claude/skills/debug-mantra/SKILL.md.

What does debug-mantra do?

It enforces a debugging order: establish a reproducible failure, trace the failure path, try to disprove candidate hypotheses, and maintain an experiment ledger. It does not propose a fix before the earlier stages are satisfied.

When does debug-mantra run?

Call it with /debug-mantra. It also activates when a user reports a bug, asks for diagnosis, or supplies a stack trace or error log.

See also

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