RegExpress

RegExpress doesn't approximate regex flavors — it runs each engine natively. Swift Regex uses Apple's built-in Regex type with RegexBuilder support and specialized pattern handlers for common use cases like email and URL validation. NSRegularExpression provides ICU-compatible matching with Unicode support, anchors-match-lines, and dot-matches-line-separators options. JavaScript runs through JavaScriptCore with support for the global, Unicode, sticky, dotAll, and multiline flags — exactly what you'd get in a browser or Node.js.

The Python engine emulates the re module with named groups, conditional patterns, verbose mode, ASCII-only matching, and locale-based behavior. PCRE2 brings the full power of Perl-compatible regular expressions: recursive patterns for matching nested structures, possessive quantifiers for backtracking control, and atomic groups for performance-critical matching. Each engine exposes its own set of options, so you can toggle case sensitivity, multiline, dotAll, verbose, Unicode, and engine-specific flags independently.

This matters because regex behavior varies between engines. A pattern that works in Python may fail in Swift. A JavaScript pattern with the sticky flag behaves differently than the same pattern without it. By testing against the actual engine your code uses, you catch flavor-specific bugs before they reach production.

The visual debugger steps through pattern execution one token at a time. You see exactly which character the engine is examining, which part of the pattern it's trying to match, and when and where it backtracks. This isn't a simplified simulation — it shows you the actual match attempts, state transitions, and failure points that the engine goes through.

The performance profiler measures execution across four phases: initialization, compilation, matching, and cleanup. The execution timeline shows the flow of pattern processing. The token performance heatmap highlights which parts of your pattern are consuming the most time, so you can target optimizations where they matter most. Memory usage tracking shows allocation patterns across the matching process.

The backtracking risk analyzer runs in real-time as you type. It detects three specific risk patterns: nested quantifiers (like (a+)+ ), wildcard quantifiers (like .*.*), and broad character class quantifiers (like [\s\S]+[\s\S]+). Each risk is flagged with a severity level, an explanation of the danger, and a concrete rewrite that eliminates the backtracking risk. The pattern optimizer takes this further by analyzing patterns for general inefficiencies, showing before-and-after comparisons, estimating improvement percentages, and explaining each suggested change.

The AI pattern assistant generates regex from natural language descriptions. Describe what you want to match — "email addresses", "dates in MM/DD/YYYY format", "phone numbers with optional country code" — and it produces 2–3 alternative patterns with confidence levels, suggested regex options, and plain English explanations. The generation engine supports multiple complexity styles from simple to aggressive, and validates each pattern at compile time before presenting it.

The pattern recommender takes a different approach: give it sample text and it automatically detects patterns for emails, URLs, dates (multiple formats), phone numbers, IP addresses, credit card numbers, postal codes, social security numbers, time formats, and generic numeric patterns. Each recommendation includes an icon, confidence level (high, medium, low), match coverage percentage, and suggested engine options.

The pattern explainer breaks down any existing pattern into plain English. It shows a component-level explanation, a full token breakdown with the role of each element, an abstract syntax tree visualization, and flags for potential issues like excessive backtracking or unnecessary capturing groups. This is invaluable for understanding patterns you've inherited from other developers or found online.

The test suite lets you create comprehensive test cases for any pattern. Define strings that should match and strings that shouldn't, specify expected capture groups, and run everything as a batch with pass/fail reporting. The edge case generator automatically produces test strings designed to break your pattern: boundary conditions, empty strings, Unicode edge cases, extremely long inputs, and pathological backtracking triggers.

The regression test runner checks your saved patterns against their test cases to catch breaking changes. If you edit a pattern and accidentally break an existing test case, you'll know immediately. The flaky test replayer lets you re-run and diagnose intermittent failures. Import test cases from CSV or plain text files to integrate with your existing test data.

Pattern comparison provides a structural diff between two patterns. It shows match differences, capture group analysis, performance comparison, segment-level differences, and a recommendation for which pattern is better. This is essential when refactoring patterns — you can verify that the new version produces identical results before deploying it.

The tutorial system offers a structured curriculum starting with basic regex fundamentals and progressing through intermediate and advanced topics like recursive patterns, lookaheads, and performance optimization. Specialized learning paths focus on web development, data validation, and text processing. Progress is tracked per lesson with completion percentages and bookmarks.

Daily puzzles generate a new regex challenge every day. Choose your difficulty level, solve the puzzle, and build your streak. The points system rewards consistent practice and creative solutions. Regex Golf challenges you to write the shortest pattern that matches all strings in a target set while excluding all strings in an anti-set. With 4 difficulty levels (beginner, intermediate, advanced, expert), 9 challenge categories, hints, and character count limits, it's a deeply engaging way to sharpen your regex skills.

The achievement system tracks milestones across every aspect of the app — patterns tested, tutorials completed, puzzles solved, golf challenges won, and more. Achievements unlock with popup celebrations, and your achievement stats sync across all your devices via iCloud.

The pattern library stores unlimited patterns (Pro) with descriptions, tags, and test cases. Organize patterns into hierarchical folders, mark favorites for quick access, and search your entire collection by name, description, or pattern content. Smart pattern naming auto-generates descriptive names based on pattern analysis, and the duplicate detector identifies redundant patterns in your library.

iCloud sync uses CloudKit with incremental updates via change tokens, conflict resolution by most-recent timestamp, and offline queueing. Everything syncs: patterns, folders, favorites, history, tutorial progress, daily puzzle completions, Regex Golf solutions, and achievement stats. On iPad and Mac, multi-window support provides six secondary window types — Pattern Library, Playground, Reference Guide, Test Suite, Pattern Insights, and Achievements — so you can work with your library open alongside your testing environment.

Export patterns in JSON (with full metadata), CSV, YAML, TOML, or plain text. Import from any of these formats or from regex101/RegExr URLs. The regexpress:// deep link scheme creates shareable URLs that open a specific pattern, sample text, and engine flavor directly in the app. Draft recovery automatically saves your work and presents a recovery prompt if the app closes unexpectedly.

The free tier gives you full access to the core testing engine across all 5 regex flavors, 7 saved patterns, 15 history items, the first tutorial module, 5 Regex Golf challenges, and a 45-second debug preview. You can write, test, and iterate on patterns without paying anything.

The Pro upgrade is a one-time purchase of $3.99 — no subscription. It unlocks the full visual debugger, performance profiler with backtracking analysis, pattern optimizer, code generation for all 6 languages, unlimited pattern storage, folders and search, iCloud sync, full tutorial curriculum, unlimited Regex Golf, test suite, advanced export/import, pattern recommendations, and custom themes. One purchase, lifetime access.