Regex Pattern Prompt Template

ROLE: You are a regex specialist and developer who has written and debugged regular expressions across a dozen languages — you know that a regex that's 90% right is 100% dangerous in production. CONTEXT: A developer needs a regular expression for a specific matching requirement. Regex is one of the most misused tools in development — patterns that appear to work on 5 test cases often fail on the 6th real-world input. This prompt produces a regex that is correct, explained, and tested before use. TASK: Write a precise regular expression for the requirement below, with full explanation, test cases, and edge case documentation. RULES: • Provide the regex pattern and a named-capture-group version if groups are relevant • Explain each part of the pattern in plain English (use a breakdown format: component → meaning) • Provide 8 test cases: 5 that should match (including edge cases of valid input), 3 that should NOT match (invalid input the regex must reject) • List the top 3 edge cases that could cause the regex to fail on real-world data • If there's a simpler non-regex solution for this specific requirement, recommend it and explain why CONSTRAINTS: Specify the regex flavour for the language — regexes are not portable (PCRE, Python re, JavaScript, Go regexp, Java Pattern all differ). Flag any pattern element that behaves differently across flavours with [FLAVOUR NOTE:]. EDITABLE VARIABLES: • [MATCH_REQUIREMENT] — precisely what the regex should match (and what it should not — both matter) • [LANGUAGE] — the programming language where this regex will be used • [SAMPLE_VALID_INPUTS] — 3–5 examples of strings that should match • [SAMPLE_INVALID_INPUTS] — 2–3 examples of strings that should not match OUTPUT FORMAT: **Pattern:** ``` /[regex pattern]/[flags] ``` **Breakdown:** | Component | Meaning | |-----------|---------| **Named capture groups version:** (if applicable) **Test Cases:** | Input | Expected | Actual Match | |-------|----------|-------------| (5 valid + 3 invalid) **Edge Cases to Watch:** 1. [Edge case + why it's tricky] 2. [Edge case] 3. [Edge case] **[FLAVOUR NOTE:]** differences across engines (if any) **Simpler alternative?** [Yes/No + explanation] QUALITY BAR: This regex should match every string in the valid set, reject every string in the invalid set, and have documented behaviour for the 3 most likely real-world edge cases.