HTML Checkbox — Reference and Common Patterns

<form action="https://splitforms.com/api/submit" method="POST">
  <input type="hidden" name="access_key" value="YOUR_ACCESS_KEY" />
  <input name="email" type="email" required />

  <!-- Single checkbox (terms agreement) -->
  <label>
    <input type="checkbox" name="agree" value="yes" required />
    I agree to the <a href="/terms">terms</a>
  </label>

  <!-- Multi-select checkbox group (same name attribute) -->
  <fieldset>
    <legend>Topics you're interested in</legend>
    <label><input type="checkbox" name="topics" value="design" /> Design</label>
    <label><input type="checkbox" name="topics" value="dev" /> Development</label>
    <label><input type="checkbox" name="topics" value="seo" /> SEO</label>
    <label><input type="checkbox" name="topics" value="content" /> Content</label>
  </fieldset>

  <!-- Single checkbox with default-checked -->
  <label>
    <input type="checkbox" name="newsletter" value="yes" checked />
    Send me the weekly newsletter
  </label>

  <button type="submit">Submit</button>
</form>

An HTML checkbox is `<input type="checkbox">`. The `value` attribute is what gets submitted when the checkbox is checked; if unchecked, the field is omitted from the submission entirely (not submitted as 'false' or empty string). This trips people up — make sure your backend handles the field-not-present case as 'unchecked'.

Multiple checkboxes with the same `name` form a group. The backend receives an array of all checked values. Example: three checkboxes named `topics` with values 'design', 'dev', 'seo' — if the user checks design and seo, the backend receives `topics=design&topics=seo`. splitforms reassembles this into an array for the dashboard.

Use `checked` to default-check a checkbox. Useful for newsletter opt-ins (the user can uncheck to opt out) or pre-filled preferences. Use `required` on a single checkbox (terms-of-service style) to block submission until checked. Required doesn't apply meaningfully to multi-select checkbox groups — there's no way to require at least one of N — for that, use a select or radio group.

Accessibility: wrap the checkbox in a `<label>` so the label text is clickable. For multi-select groups, wrap in a `<fieldset>` with `<legend>` describing the group. Screen readers announce the legend when any checkbox in the group is focused.

Same name = group. Unchecked = omitted from submission. Required blocks submit.