Why use backtick strings for Go regexes?

Go's backtick strings are raw — backslashes are literal. That lets you write `\\d+` instead of escaping every backslash. The generator emits backtick strings whenever the pattern is free of backticks.

What is the difference between Compile and MustCompile?

Compile returns an error for invalid patterns; MustCompile panics. Use MustCompile for compile-time-known patterns where a panic would indicate a programmer error.

Why does Go have no /g flag?

Go's API distinguishes globality by method name: FindString returns the first hit, FindAllString returns every hit. No /g flag is needed because the method choice expresses the same intent.

Yes. The Go snippet is assembled in your browser.

go · regexp · re2 · linear-time · local

Generate Go code from a regex

Drop a pattern in, pick flags, and get a regexp snippet — MustCompile, MatchString, FindString, FindAllString, ReplaceAllString, Split — using backtick raw strings.

Regex → Go

//g

Go uses Google's RE2 engine — no lookarounds, no backreferences. Use (?i), (?m), (?s) inline flags instead of /g.

Sample inputReplacement

package main

import (
	"fmt"
	"regexp"
)

func main() {
	input := "Reach alice@example.com or bob@test.org."
	re := regexp.MustCompile(`\\b\\w+@\\w+\\.\\w+\\b`)

	isMatch := re.MatchString(input)
	first := re.FindString(input)
	all := re.FindAllString(input, -1)
	groups := re.FindStringSubmatch(input)
	replaced := re.ReplaceAllString(input, "[email]")
	parts := re.Split(input, -1)

	fmt.Println("isMatch:", isMatch)
	fmt.Println("first:", first)
	fmt.Println("all:", all)
	fmt.Println("groups:", groups)
	fmt.Println("replaced:", replaced)
	fmt.Println("parts:", parts)
}

Quick Start

How to use a regex in Go

Go's regexp package uses RE2 — fast, linear-time, but missing lookarounds and backreferences. Flags are inline: (?i)pattern.

01
Type a pattern
Backtick raw strings keep backslashes literal — `\b…\b` instead of "\\b…\\b". The tool defaults to backtick output when the pattern is backtick-safe.
Patterns are parsed with the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) require the u flag.
patternECMAScriptliteralregex
input · literalpattern · regex
```
`\b\w+@\w+\b`
```
loaded · ECMAScripttarget · ready
02
Tune flags
Go has no flag arg — flags are inline. JS i/m/s map to (?i), (?m), (?s). The tool prefixes your pattern with the right inline group automatically.
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.
flagssampleg · i · mlive
config · optionsflags · flags
```
(?im)
```
flags applied · livelive · preview
03
Read the snippet
Includes MatchString (bool), FindString (first), FindAllString (every), FindStringSubmatch (groups), ReplaceAllString, and Split.
The generator rewrites the regex for the target language — handling string-literal escaping, raw-string prefixes, and engine-specific syntax tweaks.
codegentargetsnippetcopy
run · outputpreview · code
```
regexp.MustCompile(`…`)
```
snippet · livecode · ready
04
Copy code
One click copies the full main function — paste into a .go file and run with go run.
Copy writes via navigator.clipboard.writeText, 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 to generate Go regex code

Skip the boilerplate when wiring a pattern into a Go HTTP service, a CLI, or a Kubernetes operator.

HTTP middleware

Filter request paths with MatchString in a chi/gin handler. 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

k8s admission

Validate resource names with regexp in a custom admission webhook. 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.

k8s

CLI tools

Build cobra commands that grep or replace text matching a pattern. 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

Log shippers

Parse log lines with FindStringSubmatch in a Vector/Fluent-bit alternative. 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

ETL pipelines

Run ReplaceAllString in batch jobs over millions of rows. 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

API gateways

Route requests with pattern matching at the edge. 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

Why RE2 instead of PCRE?

Go chose RE2 for guaranteed linear-time matching — no catastrophic backtracking ever. The tradeoff: no lookarounds, no backreferences. For most validation and extraction tasks, RE2 is fast enough and safe enough.

What does MustCompile do?

Like Compile but panics on invalid patterns. Use it for patterns hard-coded into your source (you'd catch the error at startup, not runtime). Use Compile when the pattern comes from user input.

How do I get named groups?

Use re.SubexpNames() to map positional groups to names. For each match m, m[i] is the value of the i-th group, and re.SubexpNames()[i] tells you what it was named.

Is Go's regex slow?

RE2 is fast for the inputs it supports, but slower than PCRE for many practical patterns. For high-throughput regex matching consider hyperscan or a parsing alternative.

Is anything sent to a server?

No. The code is generated entirely in your browser.

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