regex-vs-llm-structured-text

name	regex-vs-llm-structured-text
description	Decision framework for choosing between regex and LLM when parsing structured text — start with regex, add LLM only for low-confidence edge cases.
source_path	skills/regex-vs-llm-structured-text/SKILL.md
origin	ECC

Regex vs LLM for Structured Text Parsing

A practical decision framework for parsing structured text (quizzes, forms, invoices, documents). The key insight: regex handles 95-98% of cases cheaply and deterministically. Reserve expensive LLM calls for the remaining edge cases.

When to Activate

• Parsing structured text with repeating patterns (questions, forms, tables)
• Deciding between regex and LLM for text extraction
• Building hybrid pipelines that combine both approaches
• Optimizing cost/accuracy tradeoffs in text processing

Decision Framework

Is the text format consistent and repeating?
├── Yes (>90% follows a pattern) → Start with Regex
│   ├── Regex handles 95%+ → Done, no LLM needed
│   └── Regex handles <95% → Add LLM for edge cases only
└── No (free-form, highly variable) → Use LLM directly

Architecture Pattern

Source Text
    │
    ▼
[Regex Parser] ─── Extracts structure (95-98% accuracy)
    │
    ▼
[Text Cleaner] ─── Removes noise (markers, page numbers, artifacts)
    │
    ▼
[Confidence Scorer] ─── Flags low-confidence extractions
    │
    ├── High confidence (≥0.95) → Direct output
    │
    └── Low confidence (<0.95) → [LLM Validator] → Output