Custom Validation Patterns for Text Fields

What Are Custom Validation Patterns?

A validation pattern is a rule that defines what input is acceptable before a form can be submitted. In Auto Form Builder, patterns use regular expressions (regex) — compact formulas that describe allowed character combinations, lengths, and structures.

For example, a product code pattern might require two uppercase letters, a hyphen, and four digits: ^[A-Z]{2}-[0-9]{4}$. A visitor who enters AB-1234 passes; ab-123 does not.

Patterns validate on two levels:

• Browser validation — Text Input fields output the HTML5 pattern attribute for instant feedback before submission
• Server-side validation — The same pattern is re-checked when the form is submitted, so invalid data cannot bypass the browser

Built-In Validation Presets

Before writing custom regex, check whether a built-in preset fits your need. In Text Field Options, the Validation dropdown includes:

• None — No format validation (length rules still apply if set)
• Email — Standard email format pattern
• URL — HTTP/HTTPS web address format
• Letters only — Alphabetic characters and spaces
• Numbers only — Digits only
• Letters and numbers — Alphanumeric characters and spaces
• Custom Pattern — Enter your own regular expression

Selecting a preset automatically sets the underlying regex pattern. Choose Custom Pattern when you need a format the presets do not cover — formatted IDs, codes with hyphens, usernames, or industry-specific identifiers.

Note: For email collection, the dedicated Email field type includes confirmation fields and domain restrictions — use that instead of a Text Input with the email preset when collecting addresses.

How to Set a Custom Validation Pattern

Step 1: Add a Text Input field

Drag Text Input from the Basic category into your form (or use a Textarea if you need multi-line input with the same validation rules).

Step 2: Open Text Field Options

Select the field and scroll to the Validation dropdown under Text Field Options.

Step 3: Choose Custom Pattern

Select Custom Pattern from the Validation dropdown. A Custom Pattern text box appears below.

Step 4: Enter your regex

Type your regular expression in the Custom Pattern field — for example, [A-Za-z]{2,10} for 2–10 letters. Do not wrap the pattern in forward slashes; enter the raw regex only.

Step 5: Add length limits (optional)

Set Minimum Length and Maximum Length alongside your pattern for an extra layer of control. Length is checked independently of the regex.

Step 6: Add help text

Use Help Text in base field settings to tell visitors the expected format — for example, “Enter your ID as XX-0000 (two letters, hyphen, four digits).” Clear instructions reduce validation errors and abandonment.

Step 7: Test submissions

Preview the form and submit both valid and invalid test entries. Invalid entries should show: “Please enter a value in the correct format.”

How Pattern Matching Works

Auto Form Builder follows HTML5 pattern semantics: the entire submitted value must match the regex — not just part of it. The server wraps your pattern the same way the browser does, so client and server results stay consistent.

Pattern validation runs only when:

• A pattern is defined on the field
• The visitor entered a non-empty value

Empty optional fields skip pattern validation. Required fields must contain a value that matches the pattern.

If a custom regex is malformed, the server fails open — it does not block submissions — so a misconfigured pattern in the builder cannot permanently break your form. Always test patterns after saving.

Common Custom Pattern Examples

Product or SKU code (two letters, hyphen, four digits)

Pattern: [A-Z]{2}-[0-9]{4}
Matches: AB-1234, XY-9876
Use case: Order forms, inventory requests, warranty registration

Username (3–20 alphanumeric characters and underscores)

Pattern: [a-zA-Z0-9_]{3,20}
Matches: user_name, Account123
Use case: Registration forms, community signup

US ZIP code (5 digits or ZIP+4)

Pattern: [0-9]{5}(-[0-9]{4})?
Matches: 90210, 90210-1234
Use case: Shipping or location forms (consider the Address field for full address collection)

Social media handle (starts with @)

Pattern: @[A-Za-z0-9_]{1,15}
Matches: @username, @Brand_Name
Use case: Influencer applications, social profile collection

Hex color code

Pattern: #[A-Fa-f0-9]{6}
Matches: #FF5733, #1a2b3c
Use case: Design brief forms, brand asset requests

Invoice or reference number (letters, numbers, hyphens only)

Pattern: [A-Za-z0-9-]+
Matches: INV-2024-001, REF12345
Use case: Support tickets, billing inquiries

Two-letter state or country code

Pattern: [A-Z]{2}
Matches: CA, NY, GB
Use case: Simple regional identifiers when a full Address field is not needed

Combining Patterns with Other Text Field Options

Minimum and maximum length

Set character limits independently of regex. A username pattern [a-zA-Z0-9_]{3,20} already enforces length in the regex, but explicit Min/Max Length settings add HTML minlength and maxlength attributes on Text Input fields for browser-level feedback.

Trim whitespace

Enable Trim Whitespace to remove leading and trailing spaces before validation and submission — preventing accidental spaces from causing pattern mismatches.

Text transform

Apply UPPERCASE, lowercase, Capitalize First Letter, or Title Case on submission to normalize input before it is stored — useful when patterns expect a specific case.

Input type

Set Input Type to Telephone or URL for mobile-friendly keyboards. For phone numbers with format validation, use the dedicated Phone field type instead of a text pattern when possible.

Required fields and conditional logic

Mark fields as required in base settings. Use conditional logic to show pattern-validated fields only when relevant — hidden conditional fields skip validation when not visible.

Textarea fields

Textarea fields share the same Validation and Custom Pattern settings. Maximum length renders as an HTML attribute on the frontend; pattern and minimum length are validated server-side on submission.

Recommended Setups by Use Case

Support ticket with order reference

• Text Input with pattern [A-Za-z0-9-]+
• Min length: 5, Max length: 20
• Help text: “Enter your order number (e.g., ORD-12345)”
• Show conditionally only when “Existing order” is selected

Event registration with dietary code

• Text Input with Letters and numbers preset
• Max length: 50
• Required when dietary restrictions checkbox is checked

Partner application with company website

• Text Input with URL validation preset
• Required, with help text showing expected format (https://example.com)

Membership form with member ID

• Custom pattern: M-[0-9]{6}
• Required, trim whitespace enabled
• Text transform: UPPERCASE

Best Practices for Custom Patterns

• Start with a preset when possible — Built-in email, URL, and alphanumeric presets cover common cases without writing regex
• Always add help text — Regex error messages are generic; tell visitors the exact format you expect
• Test edge cases — Submit values that should pass and fail, including empty, too short, and wrong character types
• Keep patterns as simple as possible — Overly complex regex is hard to maintain and debug
• Combine pattern with length limits — Defense in depth for data quality
• Use the right field type — Email, Phone, and Number fields have specialized validation; do not recreate them with text patterns unless you have a specific reason
• Enable trim whitespace — Prevents trailing spaces from failing otherwise valid entries
• Do not over-validate optional fields — Pattern checks skip empty optional fields; only require patterns when the data is truly needed

Custom Patterns vs Other Validation Methods

• Custom regex pattern — Flexible format rules for IDs, codes, and structured text
• Min/max length — Character count limits; works alongside patterns
• Built-in presets — Quick setup for email, URL, letters, numbers, alphanumeric
• Email field — Dedicated type with double-entry confirmation and domain restrictions
• Phone field — Dedicated type with phone-specific formatting options
• Number field — Min, max, step, and format validation for numeric input — not text patterns
• Required field — Ensures a value exists; does not validate format

Frequently Asked Questions

Get Started with Auto Form Builder

Add a Text Input field, choose a validation preset or enter a custom regex, and collect formatted data the first time — without manual cleanup in your submissions inbox.

Download:
Auto Form Builder on WordPress.org

Plugin last updated: Last update 23 August