# Regex Tester — Matches, Groups & Plain-English Explanation (`eliai/regex-tester`) Actor

Regex Tester: send a regex pattern plus sample text, get back every match with its capture groups and a plain-English explanation of what the pattern does. Simple JSON in, JSON out via the Apify API — pay only per result, so a quick pattern check costs next to nothing.

- **URL**: https://apify.com/eliai/regex-tester.md
- **Developed by:** [Anthony Snider](https://apify.com/eliai) (community)
- **Categories:** Developer tools, Automation
- **Stats:** 2 total users, 1 monthly users, 100.0% runs succeeded, 0 bookmarks
- **User rating**: No ratings yet

## Pricing

$20.00 / 1,000 test runs

This Actor is paid per event. You are not charged for the Apify platform usage, but only a fixed price for specific events.

Learn more: https://docs.apify.com/platform/actors/running/actors-in-store#pay-per-event

## What's an Apify Actor?

Actors are a software tools running on the Apify platform, for all kinds of web data extraction and automation use cases.
In Batch mode, an Actor accepts a well-defined JSON input, performs an action which can take anything from a few seconds to a few hours,
and optionally produces a well-defined JSON output, datasets with results, or files in key-value store.
In Standby mode, an Actor provides a web server which can be used as a website, API, or an MCP server.
Actors are written with capital "A".

## How to integrate an Actor?

If asked about integration, you help developers integrate Actors into their projects.
You adapt to their stack and deliver integrations that are safe, well-documented, and production-ready.
The best way to integrate Actors is as follows.

In JavaScript/TypeScript projects, use official [JavaScript/TypeScript client](https://docs.apify.com/api/client/js.md):

```bash
npm install apify-client
```

In Python projects, use official [Python client library](https://docs.apify.com/api/client/python.md):

```bash
pip install apify-client
```

In shell scripts, use [Apify CLI](https://docs.apify.com/cli/docs.md):

````bash
# MacOS / Linux
curl -fsSL https://apify.com/install-cli.sh | bash
# Windows
irm https://apify.com/install-cli.ps1 | iex
```bash

In AI frameworks, you might use the [Apify MCP server](https://docs.apify.com/platform/integrations/mcp.md).

If your project is in a different language, use the [REST API](https://docs.apify.com/api/v2.md).

For usage examples, see the [API](#api) section below.

For more details, see Apify documentation as [Markdown index](https://docs.apify.com/llms.txt) and [Markdown full-text](https://docs.apify.com/llms-full.txt).


# README

## Regex Tester & Explainer

Test a regular expression against sample text and get every match, capture group, named group, and position — plus a plain-English explanation of the pattern. Built for agents and developers writing extraction rules.

**Live on the Apify Store — run it instantly or call it as an agent tool via Apify MCP.**

### What you get

- **Every match** with its `index` (position) in the text
- **Capture groups** (positional) and **named groups** per match
- **Plain-English explanation** — a token-by-token breakdown of what the pattern does
- **ReDoS safety** — catastrophic-backtracking patterns are flagged, and matching is time-boxed and length-capped so a run never hangs
- Works for a single test per run; safe defaults, sane caps

### Input

```json
{
  "pattern": "(?<user>\\w+)@(?<domain>[\\w.]+)",
  "text": "Contact alice@example.com or bob@test.org for details.",
  "flags": "g",
  "explain": true
}
````

- `pattern` (string, required) — the regex, no slashes
- `text` (string, required) — text to test against
- `flags` (string, default `"g"`) — any of `g i m s u y d` (`g` is always applied)
- `explain` (boolean, default `true`) — include the plain-English explanation

### Output

```json
{
  "pattern": "(?<user>\\w+)@(?<domain>[\\w.]+)",
  "flags": "g",
  "matchCount": 2,
  "matches": [
    {
      "match": "alice@example.com",
      "index": 8,
      "groups": ["alice", "example.com"],
      "namedGroups": { "user": "alice", "domain": "example.com" }
    },
    {
      "match": "bob@test.org",
      "index": 29,
      "groups": ["bob", "test.org"],
      "namedGroups": { "user": "bob", "domain": "test.org" }
    }
  ],
  "explanation": "Pattern /(?<user>\\w+)@(?<domain>[\\w.]+)/g\nFlags: global (find all matches)\nSteps:\n1. Begin a named group \"user\"\n2. Match a word character (a-z, A-Z, 0-9, _) (one or more times)\n3. End group\n4. Match the literal text \"@\"\n5. Begin a named group \"domain\"\n6. Match any character in the set [\\w.] (one or more times)\n7. End group",
  "warnings": []
}
```

### Pricing

Pay-per-event: one charge per **test run**.

# Actor input Schema

## `pattern` (type: `string`):

The regex pattern to test (without slashes), e.g. \b\w+@\w+.\w+\b

## `text` (type: `string`):

The text to run the pattern against. Every match, capture group and named group is returned with its position.

## `flags` (type: `string`):

Regex flags: g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode), y (sticky), d (indices). 'g' is always applied.

## `explain` (type: `boolean`):

Produce a token-by-token explanation of what the pattern matches.

## Actor input object example

```json
{
  "pattern": "(?<user>\\w+)@(?<domain>[\\w.]+)",
  "text": "Contact alice@example.com or bob@test.org for details.",
  "flags": "g",
  "explain": true
}
```

# API

You can run this Actor programmatically using our API. Below are code examples in JavaScript, Python, and CLI, as well as the OpenAPI specification and MCP server setup.

## JavaScript example

```javascript
import { ApifyClient } from 'apify-client';

// Initialize the ApifyClient with your Apify API token
// Replace the '<YOUR_API_TOKEN>' with your token
const client = new ApifyClient({
    token: '<YOUR_API_TOKEN>',
});

// Prepare Actor input
const input = {
    "pattern": "(?<user>\\w+)@(?<domain>[\\w.]+)",
    "text": "Contact alice@example.com or bob@test.org for details.",
    "flags": "g"
};

// Run the Actor and wait for it to finish
const run = await client.actor("eliai/regex-tester").call(input);

// Fetch and print Actor results from the run's dataset (if any)
console.log('Results from dataset');
console.log(`💾 Check your data here: https://console.apify.com/storage/datasets/${run.defaultDatasetId}`);
const { items } = await client.dataset(run.defaultDatasetId).listItems();
items.forEach((item) => {
    console.dir(item);
});

// 📚 Want to learn more 📖? Go to → https://docs.apify.com/api/client/js/docs

```

## Python example

```python
from apify_client import ApifyClient

# Initialize the ApifyClient with your Apify API token
# Replace '<YOUR_API_TOKEN>' with your token.
client = ApifyClient("<YOUR_API_TOKEN>")

# Prepare the Actor input
run_input = {
    "pattern": "(?<user>\\w+)@(?<domain>[\\w.]+)",
    "text": "Contact alice@example.com or bob@test.org for details.",
    "flags": "g",
}

# Run the Actor and wait for it to finish
run = client.actor("eliai/regex-tester").call(run_input=run_input)

# Fetch and print Actor results from the run's dataset (if there are any)
print("💾 Check your data here: https://console.apify.com/storage/datasets/" + run["defaultDatasetId"])
for item in client.dataset(run["defaultDatasetId"]).iterate_items():
    print(item)

# 📚 Want to learn more 📖? Go to → https://docs.apify.com/api/client/python/docs/quick-start

```

## CLI example

```bash
echo '{
  "pattern": "(?<user>\\\\w+)@(?<domain>[\\\\w.]+)",
  "text": "Contact alice@example.com or bob@test.org for details.",
  "flags": "g"
}' |
apify call eliai/regex-tester --silent --output-dataset

```

## MCP server setup

```json
{
    "mcpServers": {
        "apify": {
            "command": "npx",
            "args": [
                "mcp-remote",
                "https://mcp.apify.com/?tools=eliai/regex-tester",
                "--header",
                "Authorization: Bearer <YOUR_API_TOKEN>"
            ]
        }
    }
}

```

## OpenAPI specification

```json
{
    "openapi": "3.0.1",
    "info": {
        "title": "Regex Tester — Matches, Groups & Plain-English Explanation",
        "description": "Regex Tester: send a regex pattern plus sample text, get back every match with its capture groups and a plain-English explanation of what the pattern does. Simple JSON in, JSON out via the Apify API — pay only per result, so a quick pattern check costs next to nothing.",
        "version": "0.1",
        "x-build-id": "8ij2a6eEymUcSvBHu"
    },
    "servers": [
        {
            "url": "https://api.apify.com/v2"
        }
    ],
    "paths": {
        "/acts/eliai~regex-tester/run-sync-get-dataset-items": {
            "post": {
                "operationId": "run-sync-get-dataset-items-eliai-regex-tester",
                "x-openai-isConsequential": false,
                "summary": "Executes an Actor, waits for its completion, and returns Actor's dataset items in response.",
                "tags": [
                    "Run Actor"
                ],
                "requestBody": {
                    "required": true,
                    "content": {
                        "application/json": {
                            "schema": {
                                "$ref": "#/components/schemas/inputSchema"
                            }
                        }
                    }
                },
                "parameters": [
                    {
                        "name": "token",
                        "in": "query",
                        "required": true,
                        "schema": {
                            "type": "string"
                        },
                        "description": "Enter your Apify token here"
                    }
                ],
                "responses": {
                    "200": {
                        "description": "OK"
                    }
                }
            }
        },
        "/acts/eliai~regex-tester/runs": {
            "post": {
                "operationId": "runs-sync-eliai-regex-tester",
                "x-openai-isConsequential": false,
                "summary": "Executes an Actor and returns information about the initiated run in response.",
                "tags": [
                    "Run Actor"
                ],
                "requestBody": {
                    "required": true,
                    "content": {
                        "application/json": {
                            "schema": {
                                "$ref": "#/components/schemas/inputSchema"
                            }
                        }
                    }
                },
                "parameters": [
                    {
                        "name": "token",
                        "in": "query",
                        "required": true,
                        "schema": {
                            "type": "string"
                        },
                        "description": "Enter your Apify token here"
                    }
                ],
                "responses": {
                    "200": {
                        "description": "OK",
                        "content": {
                            "application/json": {
                                "schema": {
                                    "$ref": "#/components/schemas/runsResponseSchema"
                                }
                            }
                        }
                    }
                }
            }
        },
        "/acts/eliai~regex-tester/run-sync": {
            "post": {
                "operationId": "run-sync-eliai-regex-tester",
                "x-openai-isConsequential": false,
                "summary": "Executes an Actor, waits for completion, and returns the OUTPUT from Key-value store in response.",
                "tags": [
                    "Run Actor"
                ],
                "requestBody": {
                    "required": true,
                    "content": {
                        "application/json": {
                            "schema": {
                                "$ref": "#/components/schemas/inputSchema"
                            }
                        }
                    }
                },
                "parameters": [
                    {
                        "name": "token",
                        "in": "query",
                        "required": true,
                        "schema": {
                            "type": "string"
                        },
                        "description": "Enter your Apify token here"
                    }
                ],
                "responses": {
                    "200": {
                        "description": "OK"
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "inputSchema": {
                "type": "object",
                "required": [
                    "pattern",
                    "text"
                ],
                "properties": {
                    "pattern": {
                        "title": "Regular expression",
                        "type": "string",
                        "description": "The regex pattern to test (without slashes), e.g. \\b\\w+@\\w+\\.\\w+\\b"
                    },
                    "text": {
                        "title": "Sample text",
                        "type": "string",
                        "description": "The text to run the pattern against. Every match, capture group and named group is returned with its position."
                    },
                    "flags": {
                        "title": "Flags",
                        "type": "string",
                        "description": "Regex flags: g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode), y (sticky), d (indices). 'g' is always applied.",
                        "default": "g"
                    },
                    "explain": {
                        "title": "Include plain-English explanation",
                        "type": "boolean",
                        "description": "Produce a token-by-token explanation of what the pattern matches.",
                        "default": true
                    }
                }
            },
            "runsResponseSchema": {
                "type": "object",
                "properties": {
                    "data": {
                        "type": "object",
                        "properties": {
                            "id": {
                                "type": "string"
                            },
                            "actId": {
                                "type": "string"
                            },
                            "userId": {
                                "type": "string"
                            },
                            "startedAt": {
                                "type": "string",
                                "format": "date-time",
                                "example": "2025-01-08T00:00:00.000Z"
                            },
                            "finishedAt": {
                                "type": "string",
                                "format": "date-time",
                                "example": "2025-01-08T00:00:00.000Z"
                            },
                            "status": {
                                "type": "string",
                                "example": "READY"
                            },
                            "meta": {
                                "type": "object",
                                "properties": {
                                    "origin": {
                                        "type": "string",
                                        "example": "API"
                                    },
                                    "userAgent": {
                                        "type": "string"
                                    }
                                }
                            },
                            "stats": {
                                "type": "object",
                                "properties": {
                                    "inputBodyLen": {
                                        "type": "integer",
                                        "example": 2000
                                    },
                                    "rebootCount": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "restartCount": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "resurrectCount": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "computeUnits": {
                                        "type": "integer",
                                        "example": 0
                                    }
                                }
                            },
                            "options": {
                                "type": "object",
                                "properties": {
                                    "build": {
                                        "type": "string",
                                        "example": "latest"
                                    },
                                    "timeoutSecs": {
                                        "type": "integer",
                                        "example": 300
                                    },
                                    "memoryMbytes": {
                                        "type": "integer",
                                        "example": 1024
                                    },
                                    "diskMbytes": {
                                        "type": "integer",
                                        "example": 2048
                                    }
                                }
                            },
                            "buildId": {
                                "type": "string"
                            },
                            "defaultKeyValueStoreId": {
                                "type": "string"
                            },
                            "defaultDatasetId": {
                                "type": "string"
                            },
                            "defaultRequestQueueId": {
                                "type": "string"
                            },
                            "buildNumber": {
                                "type": "string",
                                "example": "1.0.0"
                            },
                            "containerUrl": {
                                "type": "string"
                            },
                            "usage": {
                                "type": "object",
                                "properties": {
                                    "ACTOR_COMPUTE_UNITS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATASET_READS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATASET_WRITES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "KEY_VALUE_STORE_READS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "KEY_VALUE_STORE_WRITES": {
                                        "type": "integer",
                                        "example": 1
                                    },
                                    "KEY_VALUE_STORE_LISTS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "REQUEST_QUEUE_READS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "REQUEST_QUEUE_WRITES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATA_TRANSFER_INTERNAL_GBYTES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATA_TRANSFER_EXTERNAL_GBYTES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "PROXY_RESIDENTIAL_TRANSFER_GBYTES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "PROXY_SERPS": {
                                        "type": "integer",
                                        "example": 0
                                    }
                                }
                            },
                            "usageTotalUsd": {
                                "type": "number",
                                "example": 0.00005
                            },
                            "usageUsd": {
                                "type": "object",
                                "properties": {
                                    "ACTOR_COMPUTE_UNITS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATASET_READS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATASET_WRITES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "KEY_VALUE_STORE_READS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "KEY_VALUE_STORE_WRITES": {
                                        "type": "number",
                                        "example": 0.00005
                                    },
                                    "KEY_VALUE_STORE_LISTS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "REQUEST_QUEUE_READS": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "REQUEST_QUEUE_WRITES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATA_TRANSFER_INTERNAL_GBYTES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "DATA_TRANSFER_EXTERNAL_GBYTES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "PROXY_RESIDENTIAL_TRANSFER_GBYTES": {
                                        "type": "integer",
                                        "example": 0
                                    },
                                    "PROXY_SERPS": {
                                        "type": "integer",
                                        "example": 0
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}
```