Sequential Thinking

Description

Step-by-step reasoning methodology with explicit evidence collection and confidence tracking. Use for complex problems requiring careful analysis and documented decision-making.

When to Use

•Complex debugging
•Architecture decisions
•Security analysis
•Performance investigation
•Any problem with multiple possible causes
•When decisions need documentation

The Sequential Process

Step 1: Define the Question

Clearly state what you're trying to determine.

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## Question
What is causing the authentication timeout for users with special characters in passwords?

Step 2: Gather Evidence

Collect all relevant information systematically.

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## Evidence Collection

### Evidence 1: Error Logs
- Source: `logs/auth-service.log`
- Finding: Timeout occurs at password encoding step
- Confidence: High (direct observation)

### Evidence 2: Code Review
- Source: `src/auth/password.ts:42`
- Finding: URL encoding applied to password
- Confidence: High (code inspection)

### Evidence 3: Test Results
- Source: Manual testing
- Finding: Works with alphanumeric, fails with `@#$`
- Confidence: High (reproducible)

Step 3: Form Hypotheses

Generate possible explanations.

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## Hypotheses

### Hypothesis A: URL Encoding Issue
- Evidence supporting: E1, E2, E3
- Evidence against: None
- Probability: 80%

### Hypothesis B: Character Set Mismatch
- Evidence supporting: E3
- Evidence against: E2 (UTF-8 used)
- Probability: 15%

### Hypothesis C: Database Encoding
- Evidence supporting: None directly
- Evidence against: E1 (fails before DB)
- Probability: 5%

Step 4: Test Hypotheses

Verify the most likely explanation.

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## Testing

### Test for Hypothesis A
Action: Remove URL encoding, use base64 instead
Result: Password `test@123` now works
Conclusion: Hypothesis A confirmed

Step 5: Document Conclusion

State the final answer with confidence.

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## Conclusion

**Root Cause**: URL encoding in password.ts:42 mangles special characters

**Confidence**: 9/10

**Evidence Chain**:
1. Timeout at encoding step (logs)
2. URL encoding in code (review)
3. Special char passwords fail (testing)
4. Removing encoding fixes issue (verification)

**Fix**: Replace URL encoding with base64 at line 42

Output Template

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# Sequential Analysis: [Problem Description]

## Question
[Clear statement of what we're investigating]

## Evidence

### Evidence 1: [Title]
- Source: [where found]
- Finding: [what it shows]
- Confidence: [High/Medium/Low]

### Evidence 2: [Title]
...

## Hypotheses

### Hypothesis A: [Name]
- Supporting evidence: [list]
- Contradicting evidence: [list]
- Probability: [X%]

### Hypothesis B: [Name]
...

## Testing

### Test 1: [What tested]
- Action: [what was done]
- Expected: [what should happen if hypothesis true]
- Actual: [what happened]
- Result: [confirms/refutes hypothesis]

## Conclusion

**Answer**: [clear statement]
**Confidence**: [X/10]
**Key Evidence**: [most important findings]
**Recommended Action**: [what to do next]

Confidence Scoring

Score	Meaning	Evidence Required
9-10	Certain	Multiple independent confirmations
7-8	High	Strong evidence, tested hypothesis
5-6	Medium	Good evidence, some uncertainty
3-4	Low	Limited evidence, multiple possibilities
1-2	Guess	Insufficient evidence

Anti-Patterns

Jumping to Conclusions

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❌ "The bug is probably in the database"
✅ "Let me gather evidence before hypothesizing"

Confirmation Bias

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❌ Only looking for evidence supporting first guess
✅ Actively seeking contradicting evidence

Skipping Documentation

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❌ Fixing without recording reasoning
✅ Document even simple analysis for future reference

Activation

Via Mode

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Use mode: deep-research

Via Command

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Apply sequential thinking to analyze [problem]

Via Skill Reference

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Use skill: sequential-thinking

MCP Integration

This skill is powered by the Sequential Thinking MCP server:

Using the MCP Tool

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The Sequential Thinking MCP server provides the `sequentialthinking` tool.
Use it for:
- Breaking complex problems into thought sequences
- Tracking confidence and revising conclusions
- Building evidence chains with explicit reasoning
- Maintaining state across multiple reasoning steps

Tool Parameters

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thought: Your current thinking step
thoughtNumber: Current step number
totalThoughts: Estimated total steps needed
nextThoughtNeeded: Whether more steps are needed
isRevision: If revising previous thinking
needsMoreThoughts: If more analysis needed

Integration Pattern

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1. Start with initial thought defining the question
2. Gather evidence in subsequent thoughts
3. Form hypotheses with probability estimates
4. Test and verify in later thoughts
5. Conclude with confidence score

Combines Well With

•Deep research mode
•Systematic debugging skill
•Root cause tracing skill
•Security audits
•Performance investigations