Regex Match Tester & Visualizer
About Regex Flag Tester
The Regular Expression Flag Tester & Behavior Analyzer evaluates how regex flags (`g`, `i`, `m`, `s`, `u`, `y`, `v`) alter match results, newline matching (`dotAll`), multiline anchors (`^`/`$`), and Unicode case folding in real time.
How to Use Regex Flag Tester
Step 1
Enter your regex pattern and sample test text.
Step 2
Toggle individual regex flag checkboxes.
Step 3
Inspect the live updated match count, highlighted spans, and capture group tables.
Step 4
Click "Copy RegExp".
Practical Use Cases for Regex Flag Tester
Debugging Multiline (`m`) vs DotAll (`s`) Flag Behavior
Test whether `.` matches newlines (`s` flag) and whether `^` and `$` match line boundaries (`m` flag) versus string boundaries.
Testing Sticky (`y`) and Global (`g`) LastIndex Mechanics
Inspect JavaScript `regex.lastIndex` iteration mechanics when executing repeated `exec()` or `matchAll()` calls.
Input & Output Examples
Comparing Match with and without `i` (Case-Insensitive) Flag
Pattern: `/render/` vs `/render/i` | Text: "Welcome to RenderXD"
Without `i`: 0 matches | With `i`: 1 match found ("Render" at index 11)Key Features & Performance
- ✓Interactive toggles for all 7 standard flags: `g` (Global), `i` (Ignore Case), `m` (Multiline), `s` (dotAll), `u` (Unicode), `y` (Sticky), `v` (Unicode Sets).
- ✓Side-by-side comparison matrix showing exact match differences as flags are toggled.
- ✓Visualizes `lastIndex` pointer progression across matches.
- ✓100% Client-Side memory execution.
- ✓1-Click Copy configured regex.
Key Terminology & Definitions
DotAll Flag (`s`)
A flag enabling the dot (`.`) metacharacter to match line terminator characters (`\n`, `\r`), which it normally does not match.
Sticky Flag (`y`)
A flag causing the regex match to attempt matching exclusively from the exact index indicated by `lastIndex`.