Regex Builder

A simple cookie-builder-style regex builder that lets you assemble regular expressions from blocks, preview the result, and test it live.

How to run

Option 1: open directly

Open index.html in your browser.

Option 2: run a local HTTP server (recommended)

From the repo root run:

python -m http.server 4173

Then open:

• http://localhost:4173

How to test

Quick manual test in the UI

1. Start the server:

   python -m http.server 4173

2. Open http://localhost:4173
3. Try this example:
   • Click Start (^)
   • Click Word character (\w) and set quantifier to 1 or more (+)
   • Click Digit (\d) and set quantifier to between 2 and 5 ({2,5})
   • Click End ($)
   • In the tester, paste: user12 user12345 test99

Programmatic checks

Validate JavaScript syntax:

node --check app.js

What the flags mean (i, m, s, g)

• i (ignore case): letters are matched case-insensitively (cat also matches Cat).
• m (multiline): ^ and $ work for each line, not only start/end of full text.
• s (dotall): . can also match newline characters (\n).
• g (global): find all matches instead of stopping at the first one.

Tip: If you're unsure, start with only g enabled and add others only when needed.

Beginner usage guide

1. Add blocks from left to right to describe the pattern.
2. Set quantifiers in Your blocks (+, *, ?, {2,5}, etc.).
3. Enable flags in the Preview section if your case needs them.
4. Paste sample text into Tester and check how many matches you get.
5. Click Copy regex when result looks correct.

Features

• ready-made blocks (\\d, \\w, \\s, ^, $, |, .),
• custom blocks: literal, character class, and named group,
• per-block quantifiers,
• reordering blocks,
• regex preview with flags,
• live match tester.