regex

Test regular expressions against strings with live match results and shareable permalinks.

Overview

regex is a browser-based regular expression tester. Enter a pattern and a set of test strings to see which lines match, how many matches were found, and what capture groups were extracted — all computed live with no server involved. The full state is encoded in the URL so results are easy to share.

Pattern

Type a pattern into the Pattern panel. The input is displayed between / delimiters to visually reflect regex literal syntax.

The panel header shows one of three states:

valid — the pattern compiles and no test strings have been entered yet
N/M match — N of M non-empty test strings matched
error: \<message\> — the pattern is not a valid regular expression

Patterns are compiled using the browser's built-in RegExp constructor. Any pattern accepted by new RegExp(pattern, flags) is valid.

Flags

Five flag toggles sit to the right of the pattern input. Click any flag to enable or disable it.

Flag	Name	Effect
`g`	global	Find all matches in a string, not just the first
`i`	ignore case	Case-insensitive matching
`m`	multiline	`^` and `$` match the start/end of each line
`s`	dotAll	`.` matches newline characters
`u`	unicode	Treat the pattern and input as Unicode

The g flag is enabled by default. Match counts in the Results panel reflect the total number of non-overlapping matches per line.

Test Strings

Enter one test string per line in the Test Strings panel. Each non-empty line is tested independently against the pattern. The panel header shows the total line count.

Results

The Results panel shows one row per non-empty test string:

The full test string (truncated with … if it overflows)
A match badge with the number of matches found, or a no match badge
If the pattern contains capture groups, the captured values are shown as chips below the string

When no pattern is entered, or when the pattern is invalid, the results panel shows a placeholder message.

Permalinks

The URL updates live as you type — no button required. All state is encoded into a single v query parameter as a Base64-encoded JSON object:

/regex?v=<base64>

The encoded object has three fields:

{ "p": "<pattern>", "f": "<flags>", "s": "<test strings>" }

Reloading or sharing the URL fully restores the pattern, active flags, and test strings.

Use the Copy button in the Permalink row to copy the current URL to your clipboard.

Use the Reset button to clear the pattern, test strings, and all flags (resetting g to on), and return the URL to the bare /regex path.