Understand what a pattern matches
Test a small positive and negative example in the browser’s JavaScript regex dialect before transforming data.
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Developer · Regex & String Tools
Debug APIs, clean content, format data, and run release checks directly in your browser.
Common utilities for regex and string processing: tester with multiline and named-group support, replacer, meta-character escape, and HTML entity encode/decode.
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Choose matching, replacement or escaping deliberately
A regex describes matches; replacement syntax describes the resulting text; escaping makes a literal safe in one specific syntax. Applying an HTML encoder to a regex pattern does not solve regex escaping.
Rewrite matched text
Check capture-group references and the g flag. A capture group is not an extra match.
Search for literal punctuation
Escape text for use as a regex pattern. Do not reuse that result as HTML, SQL or a shell command.
Check one replacement against global replacement
Text: ab ab Pattern: (a)(b) Replacement: $2$1 No g flag: ba ab (1 match) With g: ba ba (2 matches)
Enter the pattern without slash delimiters. Compare both the output and match count. If matching literal a.b, escape the dot so it cannot match a different character.
Browser JavaScript regex is not PCRE. Complex backtracking patterns may stall the page; use small samples and simplify nested ambiguous quantifiers first.
HTML Entity Encoder & Decoder
Encode five special characters or decode HTML entities one layer
Regex & String
Regex Tester
Test JavaScript regex matches and inspect indices
Regex & String
Regex Replacer
Find and replace text using regular expressions
Regex & String
Regex Escape
Escape and unescape regex special chars
Regex & String