Basic

Looks good!
Please fill the name

<form class="simple-example" action="javascript:void(0);" novalidate>
    <div class="form-row">
        <div class="col-md-12 mb-4">
            <label for="fullName">Full Name</label>
            <input type="text" class="form-control" id="fullName" placeholder="" value="" required>
            <div class="valid-feedback">
                Looks good!
            </div>
            <div class="invalid-feedback">
                Please fill the name
            </div>
        </div>
    </div>
    <button class="btn btn-primary submit-fn mt-2" type="submit">Submit form</button>
</form>

Validated

Looks good!
Please fill the name

<form class="simple-example" action="javascript:void(0);" novalidate>
    <div class="form-row">
        <div class="col-md-12 mb-4">
            <label for="fullName">Full Name</label>
            <input type="text" class="form-control" id="fullName" placeholder="" value="" required>
            <div class="valid-feedback">
                Looks good!
            </div>
            <div class="invalid-feedback">
                Please fill the name
            </div>
        </div>
    </div>
    <button class="btn btn-primary submit-fn mt-2" type="submit">Submit form</button>
</form>

Custom styles

Looks good!
Looks good!
@
Please choose a username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip.
You must agree before submitting.

    <form class="row g-3 needs-validation" novalidate>
        <div class="col-md-4">
        <label for="validationCustom01" class="form-label">First name</label>
        <input type="text" class="form-control" id="validationCustom01" value="Mark" required>
        <div class="valid-feedback">
            Looks good!
        </div>
        </div>
        <div class="col-md-4">
        <label for="validationCustom02" class="form-label">Last name</label>
        <input type="text" class="form-control" id="validationCustom02" value="Otto" required>
        <div class="valid-feedback">
            Looks good!
        </div>
        </div>
        <div class="col-md-4">
        <label for="validationCustomUsername" class="form-label">Username</label>
        <div class="input-group has-validation">
            <span class="input-group-text" id="inputGroupPrepend">@</span>
            <input type="text" class="form-control" id="validationCustomUsername" aria-describedby="inputGroupPrepend" required>
            <div class="invalid-feedback">
            Please choose a username.
            </div>
        </div>
        </div>
        <div class="col-md-6">
        <label for="validationCustom03" class="form-label">City</label>
        <input type="text" class="form-control" id="validationCustom03" required>
        <div class="invalid-feedback">
            Please provide a valid city.
        </div>
        </div>
        <div class="col-md-3">
        <label for="validationCustom04" class="form-label">State</label>
        <select class="form-select" id="validationCustom04" required>
            <option selected disabled value="">Choose...</option>
            <option>...</option>
        </select>
        <div class="invalid-feedback">
            Please select a valid state.
        </div>
        </div>
        <div class="col-md-3">
        <label for="validationCustom05" class="form-label">Zip</label>
        <input type="text" class="form-control" id="validationCustom05" required>
        <div 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="invalidCheck" required>
            <label class="form-check-label" for="invalidCheck">
            Agree to terms and conditions
            </label>
            <div class="invalid-feedback">
            You must agree before submitting.
            </div>
        </div>
        </div>
        <div class="col-12">
        <button class="btn btn-primary" type="submit">Submit form</button>
        </div>
    </form>

Browser defaults

@

    <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>

Tooltips

Looks good!
Looks good!
@
Please choose a unique and valid username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip.

<form class="row g-3 needs-validation" novalidate>
    <div class="col-md-4 position-relative">
        <label for="validationTooltip01" class="form-label">First name</label>
        <input type="text" class="form-control" 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" 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 has-validation">
        <span class="input-group-text" id="validationTooltipUsernamePrepend">@</span>
        <input type="text" class="form-control" id="validationTooltipUsername" aria-describedby="validationTooltipUsernamePrepend" required>
        <div class="invalid-tooltip">
            Please choose a unique and valid username.
        </div>
        </div>
    </div>
    <div class="col-md-6 position-relative">
        <label for="validationTooltip03" class="form-label">City</label>
        <input type="text" class="form-control" 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" 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" id="validationTooltip05" required>
        <div class="invalid-tooltip">
        Please provide a valid zip.
        </div>
    </div>
    <div class="col-12">
        <button class="btn btn-primary" type="submit">Submit form</button>
    </div>
</form>