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Prove the pattern against realistic text as you type
Test a complete expression against three Northstar records and see the live match count before using it in code or a workflow.
Regex TesterDeveloper & Data
Build a regular expression with every match, capture group, and replacement visible.
Regex Tester evaluates a pattern against realistic sample text as you type, with controls for case-insensitive matching, multiline anchors, and dot-newline behavior. Each match shows its source position and numbered capture groups, while the replacement preview applies the complete template without changing the sample.
Start the 14-day trial in the app. No payment method is required to try Foldout.
Local tool processingFiles and tool work stay on your Mac.
100+ focused toolsFiles, PDFs, media, capture, and developer workflows.
Settings ready to goFormats, dimensions, and other values carry into the tool.
Try everything first14 days in the app. No payment method required.
What it does
Test patterns live, inspect capture groups, and preview replacements before using them.
See live results after a short typing pause instead of repeatedly pressing Run.
Toggle ignore case, multiline anchors, and dot-matches-newlines behavior.
Review every match with its source position.
Inspect numbered capture groups independently for each match.
Preview a replacement template across the complete sample.
Keep expensive patterns bounded by a timeout guard.
Pattern, groups, replacement
Prove the expression against realistic text before it reaches production.
Live matches, numbered groups, positions, flags, and the complete replacement preview stay visible from first pattern to final result.
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Inspect every numbered capture group
Foldout separates the record ID, owner, and amount for each match, so every captured value is explicit instead of guessed.
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Preview the replacement before it touches real data
Build the replacement from capture groups and inspect all transformed lines immediately, without changing the source sample.
Why it belongs
Why Regex Tester earns a place in the toolbox.
The practical details that make this job faster, clearer, or safer than doing it by hand.
Real text proves the pattern
Pattern, flags, sample records, and total matches remain visible together while the expression changes.
Capture groups stop being guesswork
Every match lists $1, $2, and subsequent groups separately, with the original match position beside it.
Replacement is preview-only
Build the template from numbered groups and inspect the complete transformed result without changing the test input.
Runaway expressions are contained
Foldout limits regex work so a pathological expression cannot hold the interface indefinitely.
How to use it
From opening the tool to saving the result.
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Enter the pattern and realistic sample text.
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Choose case, multiline, or dot-newline behavior where needed.
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Review every match, position, and capture group.
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Add a replacement template and verify the complete preview.
Questions
Before you try Regex Tester
Which regex engine does it use?
It uses the regular-expression behavior provided by macOS Foundation.
Can I inspect capture groups?
Yes. Every match lists its numbered capture groups and source position.
Can I preview find and replace?
Yes. Enter a replacement template and Foldout previews the transformed sample without modifying the source text.
What happens with a very expensive pattern?
Testing is time-bounded so the interface can recover from pathological expressions.
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