Regex Test API: Complete Developer Guide

Need to test regular expressions programmatically? This guide covers everything about regex testing via API, including pattern matching, capture groups, flags, and implementation examples in multiple programming languages.

What is a Regular Expression?

A regular expression (regex) is a pattern that describes a set of strings. Regex is used for searching, matching, and manipulating text. It's a powerful tool supported across virtually all programming languages.

Example: \b[A-Z][a-z]+\b matches capitalized words like "Hello", "World"

Regex Features

Key features supported by our regex API:

Capture Groups

Extract specific parts of matches using parentheses. Example: (\d{3})-(\d{4})

Flags

Modifiers like case-insensitive (i), global (g), and multiline (m).

Match Information

Get match positions, full matches, and group captures.

Using the Regex Test API

TinyFn provides a powerful endpoint to test regular expressions:

POST https://api.tinyfn.io/v1/text/regex-test
Headers: X-API-Key: your-api-key
Content-Type: application/json

{
  "pattern": "\\b(\\w+)@(\\w+\\.\\w+)\\b",
  "text": "Contact us at hello@example.com or support@test.org",
  "flags": "g"
}

{
  "matches": [
    {
      "match": "hello@example.com",
      "index": 14,
      "groups": ["hello", "example.com"]
    },
    {
      "match": "support@test.org",
      "index": 36,
      "groups": ["support", "test.org"]
    }
  ],
  "match_count": 2,
  "is_valid_pattern": true
}

Parameters

Code Examples

JavaScript / Node.js

const response = await fetch(
  'https://api.tinyfn.io/v1/text/regex-test',
  {
    method: 'POST',
    headers: {
      'X-API-Key': 'your-api-key',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      pattern: '\\d{3}-\\d{4}',
      text: 'Call 555-1234 or 555-5678',
      flags: 'g'
    })
  }
);
const result = await response.json();
console.log(`Found ${result.match_count} matches`);

Python

import requests

response = requests.post(
    'https://api.tinyfn.io/v1/text/regex-test',
    headers={'X-API-Key': 'your-api-key'},
    json={
        'pattern': r'\d{3}-\d{4}',
        'text': 'Call 555-1234 or 555-5678',
        'flags': 'g'
    }
)
result = response.json()
print(f"Found {result['match_count']} matches")

cURL

curl -X POST "https://api.tinyfn.io/v1/text/regex-test" \
  -H "X-API-Key: your-api-key" \
  -H "Content-Type: application/json" \
  -d '{"pattern": "\\d{3}-\\d{4}", "text": "Call 555-1234", "flags": "g"}'

Common Use Cases

• Pattern Validation: Test regex patterns before deploying
• Data Extraction: Extract specific data from text
• Input Validation: Validate user input formats
• Text Processing: Find and analyze patterns in text
• Learning Tool: Practice and understand regex patterns

Best Practices

1. Escape properly: Double-escape backslashes in JSON strings
2. Use raw strings: In Python, use r"pattern" for cleaner patterns
3. Test edge cases: Test with various inputs including empty strings
4. Avoid catastrophic backtracking: Be careful with nested quantifiers

Use via MCP

Your AI agent can call this tool directly via Model Context Protocol — no HTTP code needed. Add TinyFn to Claude Desktop, Cursor, or any MCP client:

{
  "mcpServers": {
    "tinyfn-text": {
      "url": "https://api.tinyfn.io/mcp/text/",
      "headers": {
        "X-API-Key": "your-api-key"
      }
    }
  }
}

See all text analysis tools available via MCP in our Text Analysis MCP Tools for AI Agents guide.