What is the difference between ^/$ and \\A/\\z?

In ECMAScript, ^ and $ match string start/end by default and line start/end when the m flag is set. Anchors like \\A (string start) and \\z (absolute string end) exist in PCRE, Python, Ruby, and Java but not in JavaScript.

How is a word boundary defined?

\\b matches the position between a word character (\\w — letters, digits, underscore) and a non-word character, or at the start/end of the string adjacent to a word character. The visualizer marks every such position in green.

Does enabling the m flag change \\b?

No. The m flag only affects ^ and $. Word boundary positions are unchanged by m, s, or u in ECMAScript.

Is my text processed locally?

Yes. Anchor positions are computed in-browser using the native RegExp engine. The sample never leaves your device.

anchors visualized · multiline · word boundaries

See exactly where regex anchors land

Render ^, $ and word boundaries as colored bars inside your sample text. Toggle m to flip line semantics. Runs locally.

Regex Anchor Visualizer

Anchors

multiline

Pattern

^ \b

detected

Flags

1 on

Sample

31 B

text

input · pattern + sample

//m

output · anchor positions

▌ ^ start▌ $ end▌ \b boundary

▌▌hello▌ ▌world▌▌↵
▌▌foo▌ ▌bar▌ ▌baz▌▌↵
▌▌the▌ ▌end▌▌

Quick Start

How to visualize regex anchors

Drop in your pattern and sample text, then toggle the m flag to flip line semantics.

01
Type a pattern
Anchors detected in your pattern are highlighted with matching colors below.
Patterns compile through the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) work when the u flag is on.
patternECMAScriptliterallive
input · literalpattern · regex
^\w+\b
loaded · ECMAScriptPCRE · ready
02
Toggle m flag
Multiline mode makes ^ and $ match at line boundaries instead of string ends.
Each flag character mirrors the ECMAScript literal: g enables iteration, i folds case, m anchors per line, s lets . match newlines, u unlocks proper Unicode, y is sticky, and d emits indices.
flagsoptionsg · i · mlive
config · optionsflag · flags
/^/m
flags applied · liveECMA · live
03
Read the bars
Blue bars are starts, pink bars are ends, green bars are word boundaries.
Watch for catastrophic backtracking on nested quantifiers — a common ReDoS source. The tool caps match counts to keep the page responsive on pathological patterns.
matchgroupshighlightReDoS-safe
run · outputviz · matches
|hello|
matches · livegroups · live
04
Copy or export
Grab the output as JSON, CSV, or plain text — ready for your editor or pipeline.
Copy writes via navigator.clipboard.writeText; downloads use a Blob and object URL, so nothing transits the network and the output is byte-identical to what you see on screen.
copyexportclipboardblob
export · exportedready · saved
Copied
ready to shipsuccess

Pro tips

Regex patterns that don't melt down

Use named groups

(?<year>\d{4}) reads better than $1 and survives reordering. Supported in ECMAScript 2018+.

Anchor strictly

Use ^/$ with the m flag when matching whole lines. Without anchors, partial matches sneak through.

Avoid catastrophic backtracking

Nested quantifiers like (a+)+ can explode. Run patterns through ReDoS Detector first.

Escape every literal

Backslash any meta character you want literally: \.\$\^\*\+\?\[\]\{\}\|\\.

Test edge cases

Empty string, single character, unicode, the maximum length you expect — write fixtures for each.

Patterns aren’t parsers

Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.

Use Cases

When anchor visualization helps

Designing line-anchored or boundary-aware patterns.

Teach anchors

Show concretely where ^, $ and \b land. Compiles through the JavaScript RegExp constructor — engine quirks (Unicode property escapes, sticky matching, named groups) work when their flags are on. Error messages cite the exact position of any syntax issue.

ReDoS-safe

Debug multiline

See how m flag flips line vs string semantics. Pairs with the ReDoS detector to catch catastrophic backtracking before you deploy. A pattern that handles 1k-character input fine can become a denial-of-service vector on attacker-controlled 1M-character input.

ECMA-compliant

Spot \b surprises

Confirm word boundaries fall where you expect. Output exports as JavaScript, Python re, Java util.regex, .NET System.Text.RegularExpressions, PCRE, and POSIX — language quirks are highlighted on conversion so you don't ship a JS-only pattern to a Go service.

spec-grade

Build line regexes

Design line-anchored patterns with confidence. Capture groups (named or numbered) round-trip cleanly into replacement strings, JSON output, or CSV extraction without re-typing. Backreferences ($1, ${name}) preserve semantics across languages.

cross-engine

Verify whitespace

Eyeball boundaries around punctuation. Test against edge cases — empty input, single character, max length, multibyte boundaries — to catch off-by-one and zero-length match bugs before they reach production.

test-ready

Share findings

Copy the anchor table to a ticket or chat. All matching runs client-side so secret patterns never leave the browser. Useful when the pattern itself is sensitive (PII regexes, internal data formats, security filters).

production-ready

FAQ

Frequently asked questions

What do the colors mean?

Blue marks ^, pink marks $, green marks \b (word boundary). Each bar is rendered between characters at the anchor position.

Why so many word boundaries?

A boundary occurs wherever a word character is next to a non-word character, including at the very start and end of the string.

Does the m flag affect \b?

No. \b is independent of m. Only ^ and $ flip between string-level and line-level matching.

What about \A and \Z?

They're recognised in the pattern but JavaScript does not support them at runtime. Use ^ and $ instead.

Is anything sent to a server?

No. The tool runs entirely in your browser — your pattern and sample text never leave the page.

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