Regex Tester vs Regex Tester Pattern Editor

Pasted a log line and got zero matches? When a valid pattern finds nothing, tap Check prefix: the app tries up to 32 shorter versions of your pattern on the same text and shows the longest prefix that does match and where — a clue, not a proof of the exact failing token. When it can't tell (alternation, lookaround, backreferences, several places), it says so. Then step through matches one tap at a time with context, UTF-16 ranges and numbered groups. Test patterns on your device with Dart's ECMAScript regular-expression engine. See highlighted matches, positions and capture groups. Toggle ignore case, multiline and dot all; preview replacements with capture groups. Save named favorites with flags and recall recent successful patterns. Code examples are available for JavaScript, Python, Dart, Java, Kotlin, Swift, Go, PHP and Ruby. Other engines may behave differently. This app does not execute or validate those engines. Copy is disabled for unsupported cross-engine syntax or flag combinations; verify examples in your target runtime. Browse 45 reference patterns and 10 sample texts. Reference content includes Korean. Email, URL and similar patterns are learning examples, not security or complete input validation. Matching runs in a cancellable background task with a 500 ms time limit. Limits: pattern 2,000 UTF-16 units, text/replacement 20,000 units, first 500 matches and 100,000 units of result data/output. Partial results are labelled; their total is unknown and replacement is unavailable. Simplify your input if a limit is reached. Core matching, replacement, favorites and history work offline. No ads or tracking prompt. Share only when you tap Share; sharing uses your selected app. Copied text goes to your device clipboard. English controls; reference content includes Korean.

Test a regular expression on your iPhone and see every match light up the moment you type it. Paste your text, write your pattern, and watch matches highlight character by character — no desktop, no compile step, no guessing. Most regex help on a phone is a static article you read. Regex Tester is a working engine: it runs your pattern with Foundation's NSRegularExpression (the same ICU syntax iOS itself uses), so what you see here is exactly what your app, script, or config will do. Invalid pattern? You get a plain-English reason instead of a cryptic engine dump. WHAT YOU GET - See every match highlighted inside your own test text, updating live as you type - Know exactly what each capture group grabbed — numbered and named, with character ranges - Preview a find-and-replace before you commit it, using $1 / $2 templates on your real text - Flip case-insensitive, multiline, dot-all and ignore-whitespace modes with one tap and watch results change - Start from 19 ready-made patterns for email, URL, IPv4, phone, hex color, ISO date, UUID, JWT and more — searchable and filtered by Validation, Extraction, Web and Format - Look up any token without leaving the app: character classes, anchors, quantifiers, groups, lookaround and replacement templates in a built-in cheatsheet - Bookmark the patterns you keep reusing with their test text and flags, and reload any of them in one tap PERFECT FOR - Developers who need to sanity-check a pattern away from their machine - Data and log wranglers pulling IDs, dates or fields out of messy text - Students and self-taught coders learning regex by seeing it behave, not by reading about it - Anyone writing validation rules for forms, imports or search filters WHY NOT JUST USE A WEBSITE? Online regex testers need a connection, and they want you to paste your text into someone else's server — a hard no when that text is a customer export, a log dump, or anything under NDA. This runs entirely on-device, works on a plane or in a basement, and keeps a keyboard-friendly phone layout instead of a desktop page squeezed onto a small screen. PRIVACY Every pattern, test string and result is processed on your device and stored on your device. No account, no ads, no tracking, no upload — there is no server to send anything to. FULL ACCESS Live matching, the pattern library and the basics of the syntax reference are free to use. Full Access unlocks capture-group inspection with ranges, the live replace-with-template preview, the complete cheatsheet (quantifiers, groups, lookaround, replacement templates and engine notes), and saved patterns. Choose the plan that fits: weekly, yearly, or a one-time lifetime unlock that never renews. Open the Test tab, paste the text that is giving you trouble, and write the pattern that fixes it. Terms of Use (EULA): https://web-levi.web.app/terms Privacy Policy: https://web-levi.web.app/privacy-policy Questions? tphuc.work@gmail.com