What Makes an Address 'Valid'? Address Components Explained

Defining a "Valid" Address

An address can be "valid" in three different senses, and confusing them leads to bugs and bad user experiences:

Software validation typically focuses on format and completeness. Only postal service APIs can confirm deliverability.

Required Components by Country

United States

A deliverable US address requires at minimum:

Optional but helpful:

United Kingdom

Optional:

Germany

State is not required for German postal addresses.

Japan

General Rule

Every country with a postal system requires at minimum:

Levels of Validation

Level 1: Presence Check

The simplest validation — are the required fields filled in?

function basicValidation(address) {
  if (!address.street) return 'Street address is required';
  if (!address.city) return 'City is required';
  if (!address.postalCode) return 'Postal code is required';
  return null; // Valid
}

This catches empty forms but nothing else.

Level 2: Format Validation

Check that each field matches the expected format:

function formatValidation(address, country) {
  const postalPatterns = {
    US: /^[0-9]{5}(-[0-9]{4})?$/,
    UK: /^[A-Z]{1,2}[0-9][0-9A-Z]?\s?[0-9][A-Z]{2}$/i,
    CA: /^[A-Z][0-9][A-Z]\s?[0-9][A-Z][0-9]$/i,
    DE: /^[0-9]{5}$/,
    JP: /^[0-9]{3}-[0-9]{4}$/,
  };


  const pattern = postalPatterns[country];
  if (pattern && !pattern.test(address.postalCode)) {
    return 'Invalid postal code format';
  }
  return null;
}

Level 3: Consistency Validation

Check that fields are internally consistent:

Level 4: Deliverability Validation

Use a postal service API or commercial validation service to confirm:

This requires external API calls and is typically done server-side during form submission, not on every keystroke.

Common Validity Problems

Incorrect Postal Code Ranges

Each US state has specific ZIP code ranges. Common mistakes: