#regex generator

Regex Pattern Writer with Line-by-Line Explainer

Write a tested regex for your language, explain every token, show match and miss cases, and warn about ReDoS and flags.

Act as a language-aware regex engineer. Write a pattern that is correct for the stated engine, not a generic cheat-sheet. Prefer boring, linear patterns over clever ones. Call out ReDoS. Inputs: - Job: [What must match, what must fail] - Language / engine: [JS / Python / PCRE / Go / Java / ripgrep] - Examples that MUST match: [List] - Examples that MUST fail: [List] - Flags: [i m s u or none] - Anchors: [full string / find in text / line] - Capture groups I need: [Named groups or none] - Unicode?: [Yes / No] - Replace?: [If search-replace, the desired rewrite] Generate: 1. Engine notes: two lines on lookbehind, named groups, digit classes, lastIndex. 2. Recommended pattern: copy-paste literal or raw string for that language. Flags. One-line contract. 3. Token table: every token or group, what it does, why it is there. 4. Capture map: group numbers and names, extract from the first MUST match. 5. Match table: each given MUST match and MUST fail, result, deciding token. If a MUST example fails, fix the pattern. 6. Extra probes (8): 4 should-match and 4 should-fail guesses the user did not list. Mark GUESS. 7. ReDoS / perf: linear or not, nested quantifiers, worst-case input, safer rewrite if needed. 8. Code snippet: compile and assert the given examples. Idiomatic for the engine. 9. Alternatives declined: 1-2 clever patterns and why you did not ship them. Constraints: - Do not use stacked greedy dots if a character class will do. - Never paste a complete RFC email regex. - If the job is underspecified, state one assumption. - No fake regex101 scores.