Forms

Validation

Provide valuable, actionable feedback to your users with valid and invalid states, feedback messages and tooltips.

On this page

How it works#

Here's how form validation works with felt-css:

felt-css styles validation explicitly: add .is-valid or .is-invalid to a .form-control or .form-select, for example when your server renders the form again after a failed submit. The field gets a green or red border and a matching focus ring.
A .valid-feedback / .invalid-feedback (or -tooltip) element that follows the field as a sibling is shown automatically; otherwise it stays hidden.
There is no .was-validated: felt-css does not style the :valid and :invalid pseudo-classes, so a required field never shows up as invalid on page load. If you validate in the browser, toggle .is-invalid from JavaScript (see below).
Due to constraints in how CSS works, we cannot apply styles to a <label> that comes before a form control in the DOM without the help of custom JavaScript.
All modern browsers support the constraint validation API, a series of JavaScript methods for validating form controls. You may provide custom validity messages with setCustomValidity in JavaScript.

Browser defaults#

Not interested in custom validation feedback messages or writing JavaScript to change form behaviors? All good, you can use the browser defaults: mark fields as required (or use type, pattern, min…) and leave out novalidate. Try submitting the form below. Depending on your browser and OS, you'll see a slightly different style of feedback.

While these feedback styles cannot be styled with CSS, you can still customize the feedback text through JavaScript.

<form class="row g-3">
  <div class="col-md-4">
    <label for="validationDefault01" class="form-label">First name</label>
    <input type="text" class="form-control" id="validationDefault01" value="Mark" required>
  </div>
  <div class="col-md-4">
    <label for="validationDefault02" class="form-label">Last name</label>
    <input type="text" class="form-control" id="validationDefault02" value="Otto" required>
  </div>
  <div class="col-md-4">
    <label for="validationDefaultUsername" class="form-label">Username</label>
    <div class="input-group">
      <span class="input-group-text" id="inputGroupPrepend2">@</span>
      <input type="text" class="form-control" id="validationDefaultUsername" aria-describedby="inputGroupPrepend2" required>
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationDefault03" class="form-label">City</label>
    <input type="text" class="form-control" id="validationDefault03" required>
  </div>
  <div class="col-md-3">
    <label for="validationDefault04" class="form-label">State</label>
    <select class="form-select" id="validationDefault04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
  </div>
  <div class="col-md-3">
    <label for="validationDefault05" class="form-label">Zip</label>
    <input type="text" class="form-control" id="validationDefault05" required>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input" type="checkbox" value="" id="invalidCheck2" required>
      <label class="form-check-label" for="invalidCheck2">
        Agree to terms and conditions
      </label>
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

Server side#

When your server validates the form, indicate invalid and valid form fields with .is-invalid and .is-valid. A following .invalid-feedback or .valid-feedback is shown with them.

For invalid fields, ensure that the invalid feedback/error message is associated with the relevant form field using aria-describedby (noting that this attribute allows more than one id to be referenced, in case the field already points to additional form text).

Input groups don't wrap in felt-css, and there is no .has-validation: place the feedback after the .input-group and show it with .d-block. The same goes for checkboxes: put the feedback after the .form-check.

<form class="row g-3">
  <div class="col-md-4">
    <label for="validationServer01" class="form-label">First name</label>
    <input type="text" class="form-control is-valid" id="validationServer01" value="Mark" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationServer02" class="form-label">Last name</label>
    <input type="text" class="form-control is-valid" id="validationServer02" value="Otto" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationServerUsername" class="form-label">Username</label>
    <div class="input-group">
      <span class="input-group-text" id="inputGroupPrepend3">@</span>
      <input type="text" class="form-control is-invalid" id="validationServerUsername" aria-describedby="inputGroupPrepend3 validationServerUsernameFeedback" required>
    </div>
    <div id="validationServerUsernameFeedback" class="invalid-feedback d-block">
      Please choose a username.
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationServer03" class="form-label">City</label>
    <input type="text" class="form-control is-invalid" id="validationServer03" aria-describedby="validationServer03Feedback" required>
    <div id="validationServer03Feedback" class="invalid-feedback">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationServer04" class="form-label">State</label>
    <select class="form-select is-invalid" id="validationServer04" aria-describedby="validationServer04Feedback" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div id="validationServer04Feedback" class="invalid-feedback">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationServer05" class="form-label">Zip</label>
    <input type="text" class="form-control is-invalid" id="validationServer05" aria-describedby="validationServer05Feedback" required>
    <div id="validationServer05Feedback" class="invalid-feedback">
      Please provide a valid zip.
    </div>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input" type="checkbox" value="" id="invalidCheck3" aria-describedby="invalidCheck3Feedback" required>
      <label class="form-check-label" for="invalidCheck3">
        Agree to terms and conditions
      </label>
    </div>
    <div id="invalidCheck3Feedback" class="invalid-feedback d-block">
      You must agree before submitting.
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

In the felt look, an invalid field is more than a red border: it also takes a faint tomato tint (--field-invalid), so the error still reads where the thin border gets lost in the felt texture.

Supported elements#

Validation styles are available for the following form controls and components:

<input>s and <textarea>s with .form-control (including file inputs, and up to one .form-control in input groups)
<select>s with .form-select
Floating labels

.form-check-input has no valid or invalid style; give checkboxes and radios a feedback message instead.

<form>
  <div class="mb-3">
    <label for="validationTextarea" class="form-label">Textarea</label>
    <textarea class="form-control is-invalid" id="validationTextarea" placeholder="Required example textarea" required></textarea>
    <div class="invalid-feedback">
      Please enter a message in the textarea.
    </div>
  </div>

  <div class="mb-3">
    <select class="form-select is-invalid" required aria-label="select example">
      <option value="">Open this select menu</option>
      <option value="1">One</option>
      <option value="2">Two</option>
      <option value="3">Three</option>
    </select>
    <div class="invalid-feedback">Example invalid select feedback</div>
  </div>

  <div class="mb-3">
    <input type="file" class="form-control is-invalid" aria-label="file example" required>
    <div class="invalid-feedback">Example invalid form file feedback</div>
  </div>

  <div class="mb-3">
    <button class="btn btn-primary" type="submit" disabled>Submit form</button>
  </div>
</form>

Tooltips#

If your form layout allows it, you can swap the .{valid|invalid}-feedback classes for .{valid|invalid}-tooltip classes to display validation feedback in a styled tooltip. Be sure to have a parent with position: relative on it for tooltip positioning; in the example below, .position-relative on the columns does that. Tooltips lie over what follows, so leave room for them (here with .gy-5).

<form class="row gx-3 gy-5">
  <div class="col-md-4 position-relative">
    <label for="validationTooltip01" class="form-label">First name</label>
    <input type="text" class="form-control is-valid" id="validationTooltip01" value="Mark" required>
    <div class="valid-tooltip">
      Looks good!
    </div>
  </div>
  <div class="col-md-4 position-relative">
    <label for="validationTooltip02" class="form-label">Last name</label>
    <input type="text" class="form-control is-valid" id="validationTooltip02" value="Otto" required>
    <div class="valid-tooltip">
      Looks good!
    </div>
  </div>
  <div class="col-md-4 position-relative">
    <label for="validationTooltipUsername" class="form-label">Username</label>
    <div class="input-group">
      <span class="input-group-text" id="validationTooltipUsernamePrepend">@</span>
      <input type="text" class="form-control is-invalid" id="validationTooltipUsername" aria-describedby="validationTooltipUsernamePrepend" required>
    </div>
    <div class="invalid-tooltip d-block">
      Username is taken.
    </div>
  </div>
  <div class="col-md-6 position-relative">
    <label for="validationTooltip03" class="form-label">City</label>
    <input type="text" class="form-control is-invalid" id="validationTooltip03" required>
    <div class="invalid-tooltip">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3 position-relative">
    <label for="validationTooltip04" class="form-label">State</label>
    <select class="form-select is-invalid" id="validationTooltip04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div class="invalid-tooltip">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3 position-relative">
    <label for="validationTooltip05" class="form-label">Zip</label>
    <input type="text" class="form-control is-valid" id="validationTooltip05" value="10115" required>
    <div class="valid-tooltip">
      Looks good!
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

Client side with JavaScript#

To validate in the browser with your own messages, add novalidate to the <form> (this switches off the browser's feedback bubbles but keeps the validation API) and mirror each field's validity into .is-invalid when the form is submitted:

for (const form of document.querySelectorAll('.needs-validation')) {
  form.addEventListener('submit', event => {
    if (!form.checkValidity()) {
      event.preventDefault()
      event.stopPropagation()
    }
    for (const field of form.querySelectorAll('.form-control, .form-select')) {
      field.classList.toggle('is-invalid', !field.checkValidity())
    }
  })
}