Regex Tester & Builder
Live match highlighting, capture groups and flags.
2 matches
Contact ada@veojson.com or grace@example.org for access requests.
- #1 @ 8 — ada@veojson.comgroups: [ada, veojson.com]
- #2 @ 27 — grace@example.orggroups: [grace, example.org]
RegEx Cheat Sheet — 50 Patterns That Actually Ship
50 copy-paste patterns, the full syntax table, flag reference and the traps that cause outages.
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About this tool
This tester runs your pattern with the JavaScript RegExp engine, highlights every match in the sample text, and lists capture groups per match. Flags for global, case-insensitive, multiline, dotAll and unicode matching can be toggled independently.
How to test a regular expression
Enter the pattern without slashes, choose your flags, then paste sample text. Matches are highlighted immediately and each match is listed with its index and capture groups so you can confirm the groups line up with your code.
Common regex mistakes
Forgetting to escape dots and slashes, using greedy quantifiers where lazy ones are needed, and assuming ^ and $ match line boundaries without the multiline flag are the three that bite most often.
How to use Regex Tester & Builder
- 1
Open Regex Tester & Builder
Everything runs on this page — there is nothing to install and no account required to use the free features.
- 2
Add your input
Paste or enter your values in the panel above. The tool updates as you type, so you can iterate quickly.
- 3
Review the output
Check the result, copy it with one click, and adjust the options until it matches what your system expects.
- 4
Take it further
Use the developer & api tips below to make the result production-ready, then unlock the gated extras via the form above.
Best practices
- Anchor patterns with ^ and $ when validating whole values, or you will match a substring and let bad input through.
- Prefer explicit character classes over `.` — greedy dots are the root of most catastrophic backtracking.
- Test with adversarial input: empty strings, very long strings and Unicode, not just the happy path.
- Name your groups and add comments; a regex you cannot read in six months is a liability.
- Never use regex to parse HTML, JSON or email addresses at full RFC fidelity — use a real parser.
Why Regex Tester & Builder matters
Small integration details — an encoding, a claim, a header — are where most API bugs actually live, and they are expensive to find in production logs.
Getting them right in seconds keeps debugging sessions short and prevents malformed data from reaching downstream systems.
Related free & paid tools
| Tool name | Type | Key features | Link |
|---|---|---|---|
| regex101 | Free | Multi-flavour tester with step-by-step explanation | Visit |
| RegExr | Free | Interactive cheatsheet and community patterns | Visit |
| RegexBuddyOffer | Paid | Desktop regex builder, debugger and code generator | Visit |
Links marked Offer may be partner links. They cost you nothing extra and never affect which tools we recommend.