Combines regex extraction with confidence scoring to flag low-confidence items, then validates only those items with an LLM, reducing LLM calls by ~95% versus all-LLM approaches
Includes production-ready Python patterns for regex parsing, confidence scoring, and hybrid pipeline orchestration with real metrics from a 410-item quiz parsing examp
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.cursor/skills/regex-vs-llm-structured-text
Restart Cursor to activate regex-vs-llm-structured-text. Access via /regex-vs-llm-structured-text in your agent's command palette.
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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?
โโโ Yes (>90% follows a pattern) โ Start with Regex
โ โโโ Regex handles 95%+ โ Done, no LLM needed
โ โโโ Regex handles <95% โ Add LLM for edge cases only
โโโ No (free-form, highly variable) โ Use LLM directly
import re
from dataclasses import dataclass
@dataclass(frozen=True)classParsedItem:id:str text:str choices:tuple[str,...] answer:str confidence:float=1.0defparse_structured_text(content:str)->list[ParsedItem]:"""Parse structured text using regex patterns.""" pattern = re.compile(r"(?P<id>\d+)\.\s*(?P<text>.+?)\n"r"(?P<choices>(?:[A-D]\..+?\n)+)"r"Answer:\s*(?P<answer>[A-D])", re.MULTILINE | re.DOTALL,) items =[]formatchin pattern.finditer(content): choices =tuple( c.strip()for c in re.findall(r"[A-D]\.\s*(.+)",match.group("choices"))) items.append(ParsedItem(id=match.group("id"), text=match.group("text").strip(), choices=choices, answer=match.group("answer"),))return items
2. Confidence Scoring
Flag items that may need LLM review:
@dataclass(frozen=True)classConfidenceFlag: item_id:str score:float reasons:tuple[str,...]defscore_confidence(item: ParsedItem)-> ConfidenceFlag:"""Score extraction confidence and flag issues.""" reasons =[] score =1.0iflen(item.choices)<3: reasons.append("few_choices") score -=0.3ifnot item.answer: reasons.append("missing_answer") score -=0.5iflen(item.text)<10: reasons.append("short_text") score -=0.2return ConfidenceFlag( item_id=item.id, score=max(0.0, score), reasons=tuple(reasons),)defidentify_low_confidence( items:list[ParsedItem], threshold:float=0.95,)->list[ConfidenceFlag]:"""Return items below confidence threshold.""" flags =[score_confidence(item)for item in items]return[f for f in flags if f.score < threshold]
3. LLM Validator (Edge Cases Only)
defvalidate_with_llm( item: ParsedItem, original_text:str, client,)-> ParsedItem:"""Use LLM to fix low-confidence extractions.""" response = client.messages.create( model="claude-haiku-4-5-20251001",# Cheapest model for validation max_tokens=500, messages=[{"role":"user","content":(f"Extract the question, choices, and answer from this text.\n\n"f"Text: {original_text}\n\n"f"Current extraction: {item}\n\n"f"Return corrected JSON if needed, or 'CORRECT' if accurate."),}],)# Parse LLM response and return corrected item...return corrected_item
4. Hybrid Pipeline
defprocess_document( content:str,*, llm_client=None, confidence_threshold:float=0.95,)->list[ParsedItem]:"""Full pipeline: regex -> confidence check -> LLM for edge cases."""# Step 1: Regex extraction (handles 95-98%) items = parse_structured_text(content)# Step 2: Confidence scoring low_confidence = identify_low_confidence(items, confidence_threshold)ifnot low_confidence or llm_client isNone:return items
# Step 3: LLM validation (only for flagged items) low_conf_ids ={f.item_id for f in low_confidence} result =[]for item in items:if item.idin low_conf_ids: result.append(validate_with_llm(item, content, llm_client))else: result.append(item)return result
Real-World Metrics
From a production quiz parsing pipeline (410 items):
Metric
Value
Regex success rate
98.0%
Low confidence items
8 (2.0%)
Implementation Guide
Prerequisites
โบClaude Desktop or compatible AI client with skill support
โบClear understanding of task or problem to solve
โบWillingness to iterate and refine outputs
Time Estimate
15-45 minutes depending on use case complexity
Steps
1Install skill using provided installation command
2Test with simple use case relevant to your work
3Evaluate output quality and relevance
4Iterate on prompts to improve results
5Integrate into regular workflow if valuable
Common Pitfalls
โ Expecting perfect results without iteration
โ Not providing enough context in prompts
โ Using skill for tasks outside its intended scope
โ Accepting outputs without review and validation
Best Practices
โ Do
+Start with clear, specific prompts
+Provide relevant context and constraints
+Review and refine all outputs before using
+Iterate to improve output quality
+Document successful prompt patterns
โ Don't
โDon't use without understanding skill limitations
โDon't skip validation of outputs
โDon't share sensitive information in prompts
โDon't expect skill to replace human judgment
๐ก Pro Tips
โ Be specific about desired format and style
โ Ask for multiple options to choose from
โ Request explanations to understand reasoning
โ Combine AI efficiency with human expertise
When to Use This
โ Use when
Use when skill capabilities match your task, clear ROI on time saved, and you can validate outputs. Best for repetitive tasks, learning, and quality improvement.
โ Avoid when
Avoid when task requires deep expertise you can't validate, involves sensitive decisions, or when learning process is more valuable than speed of completion.
Learning Path
1Familiarize yourself with skill capabilities and limitations
2Start with low-risk, non-critical tasks
3Progress to more complex and valuable use cases
4Build expertise through regular use and experimentation