[BUG] Data validation not performed before analysis, leading to multiple corrections

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

What Happened:

1. Incorrect row count (177 vs 169) - Failed to detect multi-line CSV fields causing inflated defect count
2. Inaccurate percentages - Calculated percentages including empty/null values instead of only populated data
3. Misaligned data not detected - Column misalignment (dates in status field, names in root cause field) went unnoticed until third correction

Root Cause:
Claude proceeded directly to analysis without performing basic data quality validation:

• No column alignment verification
• No data type checking
• No unique value inspection
• No null/empty field identification

Expected Behavior:
Before any analysis, Claude should:

1. Validate CSV structure (proper field delimiters, multi-line handling)
2. Check column alignment (verify data types match expected columns)
3. Identify and report data quality issues upfront
4. Only proceed with analysis after validation
5. Clearly document any data limitations in the report

Impact:

• User had to correct analysis 3 times
• Wasted time reviewing incorrect metrics
• Generated unreliable reports that needed regeneration

Recommendation:
Implement mandatory data validation step before analysis for all data processing tasks.

What Should Happen?

Expected Behavior:
Before any analysis, Claude should:

1. Validate CSV structure (proper field delimiters, multi-line handling)
2. Check column alignment (verify data types match expected columns)
3. Identify and report data quality issues upfront
4. Only proceed with analysis after validation
5. Clearly document any data limitations in the report

Impact:

• User had to correct analysis 3 times
• Wasted time reviewing incorrect metrics
• Generated unreliable reports that needed regeneration

Recommendation:
Implement mandatory data validation step before analysis for all data processing tasks.

Error Messages/Logs

Steps to Reproduce

Steps:

1. Open Claude Code CLI
2. Provide path to CSV file for analysis
3. Request: "Analyze this defect data and provide metrics"
4. Claude immediately calculates metrics without validation

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.107.1

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_