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Regex tester API

Run a regular expression against a text and see every match, explained.

Tests a pattern in JavaScript or RE2 (Go) syntax: every match with its groups and their character offsets, an optional replacement, and the pattern taken apart token by token in plain words. JavaScript patterns run under a one-second limit, since nested quantifiers can take exponentially long; RE2 cannot. Patterns and texts are not logged or kept. Each request counts as 10 against the rate limit.

Base URL https://api.dharun.devNo API key600 requests a minuteThis page as Markdown

Test a regular expression

GET/v1/regexPOST

An invalid pattern answers 422 with code invalid_pattern and the engine's message; a JavaScript pattern that runs out of time answers 422 with code timeout. A group that took no part in a match has a null text, which is different from an empty one.

Also takes POST: The text to test the pattern on (pattern and options in the query), or JSON {"pattern": ..., "text": ...} with the options beside them. Send it as text/plain, or as JSON {"text": "..."} with the other options beside it, up to 256 KB.

What you send here is never written to the log, and the answer is not cached.

Parameter	Description
`pattern`query, required	The regular expression, without slashes. Up to 4096 bytes.
`text`query	The text to test it on (or POST it).
`flavor`query	js (default): JavaScript syntax, with lookaround and backreferences. re2: Go's syntax, linear time. One of: js, re2.
`flags`query	Any of i (ignore case), m (^ and $ at line breaks), s (. matches line breaks). Every match is always listed, so g is not needed.
`replace`query	Replace every match with this: $1, $<name>, $& and $$ in js; ${1}, ${name} and $$ in re2.
`limit`query	Matches listed, 1 to 1000. Default 100; count goes on to the end of the text.

curl

curl "https://api.dharun.dev/v1/regex?flags=i&pattern=%28%3F%3Cstate%3E%5BA-Z%5D%7B2%7D%29%5B+-%5D%3F%28%5Cd%7B2%7D%29&text=Cars+TN+37%2C+ka-05+and+MH12"

JavaScript

const response = await fetch("https://api.dharun.dev/v1/regex?flags=i&pattern=%28%3F%3Cstate%3E%5BA-Z%5D%7B2%7D%29%5B+-%5D%3F%28%5Cd%7B2%7D%29&text=Cars+TN+37%2C+ka-05+and+MH12");
const body = await response.json();
if (!response.ok) throw new Error(body.error.message);
console.log(body.data);

Python

import requests

response = requests.get("https://api.dharun.dev/v1/regex?flags=i&pattern=%28%3F%3Cstate%3E%5BA-Z%5D%7B2%7D%29%5B+-%5D%3F%28%5Cd%7B2%7D%29&text=Cars+TN+37%2C+ka-05+and+MH12", timeout=10)
body = response.json()
if not response.ok:
    raise RuntimeError(body["error"]["message"])
print(body["data"])

Response, with lists and long text shortened

{
  "data": {
    "flavor": "js",
    "pattern": "(?<state>[A-Z]{2})[ -]?(\\d{2})",
    "flags": "i",
    "groups": [
      {
        "index": 1,
        "name": "state"
      },
      {
        "index": 2
      }
    ],
    "count": 3,
    "truncated": false,
    "matches": [
      {
        "text": "TN 37",
        "start": 5,
        "end": 10,
        "groups": [
          {
            "index": 1,
            "name": "state",
            "text": "TN",
            "start": 5,
            "end": 7
          },
          {
            "index": 2,
            "text": "37",
            "start": 8,
            "end": 10
          }
        ]
      },
      {
        "text": "ka-05",
        "start": 12,
        "end": 17,
        "groups": [
          {
            "index": 1,
            "name": "state",
            "text": "ka",
            "start": 12,
            "end": 14
          },
          {
            "index": 2,
            "text": "05",
            "start": 15,
            "end": 17
          }
        ]
      },
      {
        "text": "MH12",
        "start": 22,
        "end": 26,
        "groups": [
          {
            "index": 1,
            "name": "state",
            "text": "MH",
            "start": 22,
            "end": 24
          },
          {
            "index": 2,
            "text": "12",
            "start": 24,
            "end": 26
          }
        ]
      }
    ],
    "explanation": [
      {
        "token": "(?<state>",
        "depth": 0,
        "meaning": "Start of capturing group 1, named \"state\"."
      },
      {
        "token": "[A-Z]",
        "depth": 1,
        "meaning": "One character: “A” to “Z”."
      },
      {
        "token": "{2}",
        "depth": 1,
        "meaning": "Repeats the item before it exactly 2 times."
      }
    ]
  },
  "meta": {
    "note": "JavaScript syntax, run by regexp2 in ECMAScript mode. It agrees with browsers and Node.js in nearly every case; a backreference such as \\1 in a pattern that mix…"
  }
}

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