Parallel Debugging

Framework for debugging complex issues using the Analysis of Competing Hypotheses (ACH) methodology with parallel agent investigation.

When to Use This Skill

Bug has multiple plausible root causes

Initial debugging attempts haven't identified the issue

Issue spans multiple modules or components

Need systematic root cause analysis with evidence

Want to avoid confirmation bias in debugging

Hypothesis Generation Framework

Generate hypotheses across 6 failure mode categories:

1. Logic Error

Incorrect conditional logic (wrong operator, missing case)

Off-by-one errors in loops or array access

Missing edge case handling

Incorrect algorithm implementation

2. Data Issue

Invalid or unexpected input data

Type mismatch or coercion error

Null/undefined/None where value expected

Encoding or serialization problem

Data truncation or overflow

3. State Problem

Race condition between concurrent operations

Stale cache returning outdated data

Incorrect initialization or default values

Unintended mutation of shared state

State machine transition error

4. Integration Failure

API contract violation (request/response mismatch)

Version incompatibility between components

Configuration mismatch between environments

Missing or incorrect environment variables

Network timeout or connection failure

5. Resource Issue

Memory leak causing gradual degradation

Connection pool exhaustion

File descriptor or handle leak

Disk space or quota exceeded

CPU saturation from inefficient processing

6. Environment

Missing runtime dependency

Wrong library or framework version

Platform-specific behavior difference

Permission or access control issue

Timezone or locale-related behavior

Evidence Collection Standards

What Constitutes Evidence

Evidence Type

Strength

Example

Direct

Strong

Code at

file.ts:42

shows

if (x > 0)

should be

if (x >= 0)

Correlational

Medium

Error rate increased after commit

abc123

Testimonial

Weak

"It works on my machine"

Absence

Variable

No null check found in the code path

Citation Format

Always cite evidence with file:line references:

Evidence: The validation function at src/validators/user.ts:87

does not check for empty strings, only null/undefined. This allows

empty email addresses to pass validation.

Confidence Levels

Level

Criteria

High (>80%)

Multiple direct evidence pieces, clear causal chain, no contradicting evidence

Medium (50-80%)

Some direct evidence, plausible causal chain, minor ambiguities

Low (<50%)

Mostly correlational evidence, incomplete causal chain, some contradicting evidence

Result Arbitration Protocol

After all investigators report:

Step 1: Categorize Results

Confirmed

High confidence, strong evidence, clear causal chain

Plausible

Medium confidence, some evidence, reasonable causal chain

Falsified

Evidence contradicts the hypothesis

Inconclusive

Insufficient evidence to confirm or falsify Step 2: Compare Confirmed Hypotheses If multiple hypotheses are confirmed, rank by: Confidence level Number of supporting evidence pieces Strength of causal chain Absence of contradicting evidence Step 3: Determine Root Cause If one hypothesis clearly dominates: declare as root cause If multiple hypotheses are equally likely: may be compound issue (multiple contributing causes) If no hypotheses confirmed: generate new hypotheses based on evidence gathered Step 4: Validate Fix Before declaring the bug fixed: Fix addresses the identified root cause Fix doesn't introduce new issues Original reproduction case no longer fails Related edge cases are covered Relevant tests are added or updated