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Free Regex Tester API - Debug Regular Expressions Programmatically
Regular expressions are powerful but notoriously hard to debug. Testing patterns manually, validating syntax, and tracking capture groups in your code is time-consuming and error-prone. What if you could test regex patterns via REST API and get detailed match information (indices, groups, captures) automatically?
The Regex Tester & Analyzer API lets you test, validate, replace, and split text using regex patterns—all from a simple HTTP endpoint. No installation. No setup. Just POST your pattern and text, get back structured results in milliseconds.
Why Use This API?
Testing regex locally requires writing code. Debugging requires tools like regex101 or regexr. But:
- regex101 / regexr = Web UI only, no automation, no API access
- This API = REST endpoint, automated testing, detailed match info, pre-built pattern library
Use cases range from data validation pipelines to interactive tutorials where users submit patterns and see real-time results.
Quick Example - cURL
# Test a regex pattern
curl -X POST "https://regex-tester-api.p.rapidapi.com/test" \
-H "X-RapidAPI-Key: YOUR_KEY" \
-H "X-RapidAPI-Host: regex-tester-api.p.rapidapi.com" \
-H "Content-Type: application/json" \
-d '{"pattern": "\\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,}\\b", "text": "Contact us at support@example.com or sales@test.org", "flags": "gi"}'
Response:
{
"success": true,
"pattern": "\\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,}\\b",
"flags": "gi",
"match_count": 2,
"matches": [
{
"match": "support@example.com",
"index": 16,
"length": 19,
"captures": ["support", "example.com"]
}
],
"execution_time_ms": 0.8
}
Python Example
import requests
import json
url = "https://regex-tester-api.p.rapidapi.com/test"
headers = {
"X-RapidAPI-Key": "YOUR_API_KEY",
"X-RapidAPI-Host": "regex-tester-api.p.rapidapi.com",
"Content-Type": "application/json"
}
# Extract IP addresses from log
payload = {
"pattern": r"(\d{1,3}\.){3}\d{1,3}",
"text": "Server logs: 192.168.1.1 down, 10.0.0.1 responding, failed at 255.255.255.0",
"flags": "g"
}
response = requests.post(url, json=payload, headers=headers)
data = response.json()
if data["success"]:
for match in data["matches"]:
print(f"IP: {match['match']} at position {match['index']}")
else:
print(f"Error: {data.get('error')}")
JavaScript / Node.js Example
const axios = require("axios");
const testRegex = async () => {
const response = await axios.post(
"https://regex-tester-api.p.rapidapi.com/test",
{
pattern: "(\\w+)@([\\w.]+)",
text: "Notify alice@example.com and bob@company.co.uk when done",
flags: "g"
},
{
headers: {
"X-RapidAPI-Key": process.env.RAPIDAPI_KEY,
"X-RapidAPI-Host": "regex-tester-api.p.rapidapi.com"
}
}
);
response.data.matches.forEach(m => {
console.log(`Email: ${m.match} (user: ${m.captures[0]}, domain: ${m.captures[1]})`);
});
};
testRegex();
Key Features
1. Pattern Testing (/test)
Test regex patterns against text. Get:
- All matches with positions (indices)
- Capture groups and sub-matches
- Execution time
- Match count
2. Regex Validation (/validate)
Check regex syntax before deploying to production. Catches syntax errors like unbalanced brackets, invalid flags, etc.
curl -X POST "https://regex-tester-api.p.rapidapi.com/validate" \
-H "X-RapidAPI-Key: YOUR_KEY" \
-d '{"pattern": "[unclosed"}'
3. Find & Replace (/replace)
Perform regex-based replacements with backreferences ($1, $2, etc.).
curl -X POST "https://regex-tester-api.p.rapidapi.com/replace" \
-H "X-RapidAPI-Key: YOUR_KEY" \
-d '{"pattern": "(\\d{4})-(\\d{2})-(\\d{2})", "text": "Date: 2025-01-15", "replacement": "$2/$3/$1"}'
Result: Date: 01/15/2025
4. Split Text (/split)
Split strings by regex delimiters, useful for parsing structured text.
5. Pattern Library (/library)
Access 30+ battle-tested patterns pre-built for common scenarios:
- Email validation
- URL extraction
- IP address matching
- Phone numbers
- Credit card formats
- Timestamps and dates
No need to write patterns from scratch—use the library and customize as needed.
Real-World Use Cases
1. Log Analysis & Data Extraction
Extract IPs, timestamps, error codes, usernames from logs. Get precise indices to locate and process the data.
# Extract failed login attempts
payload = {
"pattern": r"ERROR: Login failed for user (\w+) at (\d{2}:\d{2}:\d{2})",
"text": open("app.log").read(),
"flags": "m"
}
2. Input Validation Before Deployment
Test your production regex against various test cases via API instead of hardcoding untested patterns.
3. PII Redaction & Data Cleaning
Anonymize email addresses, phone numbers, SSNs, credit cards in datasets using find-and-replace with backreferences.
# Redact email domains
curl -X POST "...regex-tester-api.p.rapidapi.com/replace" \
-d '{"pattern": "@[^\\s]+", "text": "Contact alice@company.com", "replacement": "@hidden"}'
Result: Contact alice@hidden
4. Interactive Regex Tutorials
Build educational tools where students submit patterns, see instant match results, and understand capture groups visually.
5. Text Processing Pipelines
Normalize data: reformat dates, extract/validate fields, split structured text into components for downstream processing.
Pricing
| Plan | Cost | Requests/Month | Best For |
|---|---|---|---|
| Free | $0 | 500 | Testing, development |
| Pro | $5.99 | 50,000 | Production workflows |
| Ultra | $14.99 | 500,000 | Enterprise pipelines |
Related APIs
Looking for more text processing tools? Check out:
- Text Analysis API – Analyze sentiment, keywords, readability
- Text Diff API – Compare before/after regex replacements
- Email Validation API – Validate emails extracted by regex
- String Utilities API – Trim, split, reverse, encode strings
Get Started Now
Test this API free on RapidAPI
No credit card required. 500 free requests to test your regex patterns instantly.
Found this useful? Share it with your team. Drop a comment below if you have questions about using regex via API or need help with specific patterns.
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