JSON to RegEx Generator

About This Tool

Generate regular expression patterns from your JSON structure and values. This tool runs entirely in your browser — no data is ever sent to a server. Free to use, no account required.

What the JSON Regex Generator Does

The regex generator creates regular expression patterns for validating JSON string fields, saving time compared to writing patterns from scratch.

Pattern Generation from Examples

Provide example valid values and the tool infers a regex pattern that matches all of them. For example, provide several phone number examples and the tool generates a pattern that validates that format.

Common JSON Field Patterns

A library of ready-made patterns covers the most common validation needs: email address, URL, ISO 8601 date, UUID, IPv4 address, credit card number, zip code, and hex color code.

Using Regex in JSON Schema

Generated patterns integrate directly into JSON Schema validation via the pattern keyword.

The pattern Keyword

Add "pattern": "your-regex-here" to any string type field in your JSON Schema. The value must match the regex (using ECMA 262 dialect) for the schema validation to pass. The pattern must match the complete string, not just a substring.

Testing Your Patterns

Always test regex patterns against both valid examples (which should match) and invalid examples (which should not) before deploying. Edge cases like empty strings, unicode characters, and boundary values often reveal pattern issues.

Ready-to-Use Regex Patterns for Common JSON Fields

Copy these tested regex patterns directly into your JSON Schema pattern keyword. All patterns use ECMA 262 regex dialect, compatible with JSON Schema validators and JavaScript.

Complete JSON Schema Example with Regex Validation

Here is a real-world JSON Schema that uses pattern to validate multiple fields in a user registration object. Copy and adapt it for your own API.

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "User Registration",
  "type": "object",
  "required": ["email", "username", "birthDate"],
  "properties": {
    "email": {
      "type": "string",
      "pattern": "^[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,}$",
      "description": "Valid email address"
    },
    "username": {
      "type": "string",
      "pattern": "^[a-z0-9_]{3,20}$",
      "description": "3-20 lowercase alphanumeric characters or underscores"
    },
    "birthDate": {
      "type": "string",
      "pattern": "^\d{4}-\d{2}-\d{2}$",
      "description": "ISO 8601 date (YYYY-MM-DD)"
    },
    "website": {
      "type": "string",
      "pattern": "^https?:\/\/.+",
      "description": "Optional URL starting with http or https"
    },
    "phoneNumber": {
      "type": "string",
      "pattern": "^\+[1-9]\d{1,14}$",
      "description": "E.164 international phone number"
    }
  }
}

Key Rules When Using pattern in JSON Schema

• The pattern keyword uses ECMA 262 regex (same as JavaScript). Avoid PCRE-only features like lookbehind assertions.
• Patterns are not anchored by default — a pattern of \d{4} will match "hello1234world". Always anchor with ^ and $ to require a full match.
• Backslashes in JSON strings must be double-escaped: write \\d in JSON to represent the regex \d.
• The pattern keyword only applies to values of type string. It is ignored for other types.
• Always test your pattern against at least 5 valid and 5 invalid examples before using in production.

Common JSON Field Regex Patterns

The table below lists ready-to-use regex patterns for the most common field types found in JSON APIs. All patterns are anchored with ^ and $ to require a full match, preventing partial matches on fields like "hello1234" satisfying a \d{4} pattern.

Using Generated Regex in JSON Schema

JSON Schema's pattern keyword validates string values against a regex. Remember that JSON requires backslashes to be double-escaped: write \\d in the JSON string to represent the regex \d.

{
  "$schema": "https://json-schema.org/draft/2020-12",
  "type": "object",
  "properties": {
    "email": {
      "type": "string",
      "pattern": "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$"
    },
    "createdAt": {
      "type": "string",
      "pattern": "^\\d{4}-\\d{2}-\\d{2}T\\d{2}:\\d{2}:\\d{2}",
      "description": "ISO 8601 datetime"
    },
    "userId": {
      "type": "string",
      "pattern": "^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$"
    }
  }
}