Regex Tester

Programmatic Access

Regex Tester is also callable as a free HTTP JSON API at https://aidevhub.io/api/regex-tester/ — GET with query parameters or POST with a JSON body, no authentication, CORS enabled, 50 requests/day per IP. Responses return { ok, tool, result, meta }.

curl -s "https://aidevhub.io/api/regex-tester/?pattern=%5Cd%2B&text=abc%20123%20def%20456&flags=g"

Machine-readable contract: /api/tool/regex-tester.json · All API endpoints: /agents/ · LLM site index: /llms.txt

Agent Invocation

REST API

curl "https://aidevhub.io/api/regex-tester/?pattern=%5Cd%2B&text=abc+123+def+456&flags=g"

const res = await fetch("https://aidevhub.io/api/regex-tester//api/regex-tester/", {
  method: "GET",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
  "pattern": "\\d+",
  "text": "abc 123 def 456",
  "flags": "g"
}),
});
const data = await res.json();
console.log(data);

import requests

res = requests.post(
    "https://aidevhub.io/api/regex-tester//api/regex-tester/",
    json={"pattern":"\\d+","text":"abc 123 def 456","flags":"g"},
)
print(res.json())

{
  "valid": true,
  "pattern": "\\d+",
  "matches": [
    {
      "match": "123",
      "index": 4
    }
  ],
  "match_count": 2
}

How to Use Regex Tester

1. 1

   Enter your regex pattern

   Type a regular expression in the pattern field (e.g., `^[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$` for email). Use flags (g, i, m) as needed.

2. 2

   Input test strings to match against

   Paste or type multiple test strings in the input field. The tool will highlight all matches in real-time as you type.

3. 3

   View matches and capture groups

   See all matches highlighted with their exact positions. If your pattern has capture groups (parentheses), see the captured values listed separately.

4. 4

   Check regex explanation

   Read the auto-generated English explanation of what your regex does. This helps you debug patterns or learn regex syntax.

5. 5

   Test edge cases and iterate

   Add more test strings to cover edge cases (empty strings, special chars, long text). Refine your pattern until all cases pass.

Frequently Asked Questions

How do I test a regex pattern against a string online?

Enter the pattern between the two slashes, pick your flags, and paste the text to search into the test string box. Matches highlight immediately, and the details panel lists each match with its character index plus any numbered or named capture groups. The engine is your browser's own JavaScript RegExp, so behavior matches what you will see in Node.js or front-end code.

Step by step

1. Type the pattern without surrounding slashes — the tester adds the /.../ delimiters for you.
2. Toggle flags: keep g on to find every match instead of stopping at the first.
3. Paste your test text. Each match is highlighted in a distinct color, with index and capture groups in the side panel.
4. Need a starting point? The Patterns menu inserts presets for emails, URLs, IPv4 addresses, ISO dates, hex colors, and more.
5. Enable Replace mode to preview substitutions — $1, $2, and $& backreferences are supported.
6. Copy the matched strings out with the Copy Matches button when you are done.

Test a regex from the command line (dedicated API)

The same matcher is exposed as a REST endpoint, so scripts and agents can test patterns without a browser:

curl "https://aidevhub.io/api/regex-tester/?pattern=%5Cd%2B&text=abc+123+def+456&flags=g"

The response reports validity, the pattern, each match with its index, and a match count — for example {"valid": true, "pattern": "\\d+", "matches": [{"match": "123", "index": 4}], "match_count": 2}. GET and POST are both accepted; the free tier is rate-limited to 50 requests per day.

Which regex flags does this tester support?

Flags as implemented in this tester's UI (JavaScript RegExp semantics). The sticky (y) and hasIndices (d) flags are not exposed here.

Why does my regex only find one match?

Almost always a missing g flag. Without it, a JavaScript regex returns only the first match — the same code pasted into String.replace will then replace only one occurrence. The tester mirrors that behavior so what you see here is what your code will do.

Is it safe to paste production data into this tester?

The in-browser tester never transmits your pattern or test text; matching runs entirely in the page. Log lines and payloads you paste stay on your machine and are discarded when you close the tab. Only the optional REST API sends data to a server — use the browser tool when the text is sensitive.