diff --git a/owrx/controllers/settings/__init__.py b/owrx/controllers/settings/__init__.py
index c96645c..85bd2a9 100644
--- a/owrx/controllers/settings/__init__.py
+++ b/owrx/controllers/settings/__init__.py
@@ -1,6 +1,7 @@
 from owrx.config import Config
 from owrx.controllers.admin import AuthorizationMixin
 from owrx.controllers.template import WebpageController
+from owrx.form.error import FormError
 from abc import ABCMeta, abstractmethod
 from urllib.parse import parse_qs
 
@@ -10,16 +11,16 @@ class Section(object):
         self.title = title
         self.inputs = inputs
 
-    def render_input(self, input, data):
-        return input.render(data)
+    def render_input(self, input, data, errors):
+        return input.render(data, errors)
 
-    def render_inputs(self, data):
-        return "".join([self.render_input(i, data) for i in self.inputs])
+    def render_inputs(self, data, errors):
+        return "".join([self.render_input(i, data, errors) for i in self.inputs])
 
     def classes(self):
         return ["col-12", "settings-section"]
 
-    def render(self, data):
+    def render(self, data, errors):
         return """
             <div class="{classes}">
                 <h3 class="settings-header">
@@ -28,11 +29,20 @@ class Section(object):
                 {inputs}
             </div>
         """.format(
-            classes=" ".join(self.classes()), title=self.title, inputs=self.render_inputs(data)
+            classes=" ".join(self.classes()), title=self.title, inputs=self.render_inputs(data, errors)
         )
 
     def parse(self, data):
-        return {k: v for i in self.inputs for k, v in i.parse(data).items()}
+        parsed_data = {}
+        errors = []
+        for i in self.inputs:
+            try:
+                parsed_data.update(i.parse(data))
+            except FormError as e:
+                errors.append(e)
+            except Exception as e:
+                errors.append(FormError(i.id, "{}: {}".format(type(e).__name__, e)))
+        return parsed_data, errors
 
 
 class SettingsController(AuthorizationMixin, WebpageController):
@@ -41,6 +51,10 @@ class SettingsController(AuthorizationMixin, WebpageController):
 
 
 class SettingsFormController(AuthorizationMixin, WebpageController, metaclass=ABCMeta):
+    def __init__(self, handler, request, options):
+        super().__init__(handler, request, options)
+        self.errors = {}
+
     @abstractmethod
     def getSections(self):
         pass
@@ -52,8 +66,11 @@ class SettingsFormController(AuthorizationMixin, WebpageController, metaclass=AB
     def getData(self):
         return Config.get()
 
+    def getErrors(self):
+        return self.errors
+
     def render_sections(self):
-        sections = "".join(section.render(self.getData()) for section in self.getSections())
+        sections = "".join(section.render(self.getData(), self.getErrors()) for section in self.getSections())
         buttons = self.render_buttons()
         return """
             <form class="settings-body" method="POST">
@@ -84,15 +101,34 @@ class SettingsFormController(AuthorizationMixin, WebpageController, metaclass=AB
 
     def parseFormData(self):
         data = parse_qs(self.get_body().decode("utf-8"), keep_blank_values=True)
-        return {k: v for i in self.getSections() for k, v in i.parse(data).items()}
+        result = {}
+        errors = []
+        for section in self.getSections():
+            section_data, section_errors = section.parse(data)
+            result.update(section_data)
+            errors += section_errors
+        return result, errors
 
     def getSuccessfulRedirect(self):
         return self.request.path
 
+    def _mergeErrors(self, errors):
+        result = {}
+        for e in errors:
+            if e.getKey() not in result:
+                result[e.getKey()] = []
+            result[e.getKey()].append(e.getMessage())
+        return result
+
     def processFormData(self):
-        self.processData(self.parseFormData())
-        self.store()
-        self.send_redirect(self.getSuccessfulRedirect())
+        data, errors = self.parseFormData()
+        if errors:
+            self.errors = self._mergeErrors(errors)
+            self.indexAction()
+        else:
+            self.processData(data)
+            self.store()
+            self.send_redirect(self.getSuccessfulRedirect())
 
     def processData(self, data):
         config = self.getData()
diff --git a/owrx/controllers/settings/sdr.py b/owrx/controllers/settings/sdr.py
index a655a6d..524f1b1 100644
--- a/owrx/controllers/settings/sdr.py
+++ b/owrx/controllers/settings/sdr.py
@@ -8,6 +8,7 @@ from owrx.controllers.settings import Section
 from urllib.parse import quote, unquote
 from owrx.sdr import SdrService
 from owrx.form import TextInput, DropdownInput, Option
+from owrx.form.validator import RequiredValidator
 from owrx.property import PropertyLayer, PropertyStack
 from abc import ABCMeta, abstractmethod
 
@@ -235,7 +236,7 @@ class SdrDeviceController(SdrFormControllerWithModal):
         if self.device is None:
             self.send_response("device not found", code=404)
             return
-        self.serve_template("settings/general.html", **self.template_variables())
+        super().indexAction()
 
     def processFormData(self):
         if self.device is None:
@@ -276,7 +277,7 @@ class NewSdrDeviceController(SettingsFormController):
                 "New device settings",
                 TextInput("name", "Device name"),
                 DropdownInput("type", "Device type", [Option(name, name) for name in SdrDeviceDescription.getTypes()]),
-                TextInput("id", "Device ID"),
+                TextInput("id", "Device ID", validator=RequiredValidator()),
             )
         ]
 
@@ -331,7 +332,7 @@ class SdrProfileController(SdrFormControllerWithModal):
         if self.profile is None:
             self.send_response("profile not found", code=404)
             return
-        self.serve_template("settings/general.html", **self.template_variables())
+        super().indexAction()
 
     def processFormData(self):
         if self.profile is None:
@@ -377,7 +378,7 @@ class NewProfileController(SdrProfileController):
         return [
             Section(
                 "New profile settings",
-                TextInput("id", "Profile ID"),
+                TextInput("id", "Profile ID", validator=RequiredValidator()),
             )
         ] + super().getSections()
 
diff --git a/owrx/form/__init__.py b/owrx/form/__init__.py
index f53cc00..4968c1e 100644
--- a/owrx/form/__init__.py
+++ b/owrx/form/__init__.py
@@ -1,16 +1,18 @@
-from abc import ABC, abstractmethod
+from abc import ABC
 from owrx.modes import Modes
 from owrx.config import Config
+from owrx.form.validator import Validator
 from owrx.form.converter import Converter, NullConverter, IntConverter, FloatConverter, EnumConverter
 from enum import Enum
 
 
 class Input(ABC):
-    def __init__(self, id, label, infotext=None, converter: Converter = None, disabled=False, removable=False):
+    def __init__(self, id, label, infotext=None, converter: Converter = None, validator: Validator = None, disabled=False, removable=False):
         self.id = id
         self.label = label
         self.infotext = infotext
         self.converter = self.defaultConverter() if converter is None else converter
+        self.validator = validator
         self.disabled = disabled
         self.removable = removable
 
@@ -24,7 +26,6 @@ class Input(ABC):
         return NullConverter()
 
     def bootstrap_decorate(self, input):
-        infotext = "<small>{text}</small>".format(text=self.infotext) if self.infotext else ""
         return """
             <div class="form-group row" data-field="{id}">
                 <label class="col-form-label col-form-label-sm col-3" for="{id}">{label}</label>
@@ -40,19 +41,22 @@ class Input(ABC):
             id=self.id,
             label=self.label,
             input=input,
-            infotext=infotext,
+            infotext="<small>{text}</small>".format(text=self.infotext) if self.infotext else "",
             removable="removable" if self.removable else "",
             removebutton='<button type="button" class="btn btn-sm btn-danger option-remove-button">Remove</button>'
             if self.removable
             else "",
         )
 
-    def input_classes(self):
-        return " ".join(["form-control", "form-control-sm"])
+    def input_classes(self, error):
+        classes = ["form-control", "form-control-sm"]
+        if error:
+            classes.append("is-invalid")
+        return " ".join(classes)
 
-    def input_properties(self, value):
+    def input_properties(self, value, error):
         props = {
-            "class": self.input_classes(),
+            "class": self.input_classes(error),
             "id": self.id,
             "name": self.id,
             "placeholder": self.label,
@@ -62,26 +66,35 @@ class Input(ABC):
             props["disabled"] = "disabled"
         return props
 
-    def render_input_properties(self, value):
-        return " ".join('{}="{}"'.format(prop, value) for prop, value in self.input_properties(value).items())
+    def render_input_properties(self, value, error):
+        return " ".join('{}="{}"'.format(prop, value) for prop, value in self.input_properties(value, error).items())
 
-    def render_input(self, value):
-        return "<input {properties} />".format(properties=self.render_input_properties(value))
+    def render_errors(self, errors):
+        return "".join("""<div class="invalid-feedback">{msg}</div>""".format(msg=e) for e in errors)
 
-    def render(self, config):
+    def render_input(self, value, errors):
+        return "<input {properties} />{errors}".format(
+            properties=self.render_input_properties(value, errors), errors=self.render_errors(errors)
+        )
+
+    def render(self, config, errors):
         value = config[self.id] if self.id in config else None
-        return self.bootstrap_decorate(self.render_input(self.converter.convert_to_form(value)))
+        error = errors[self.id] if self.id in errors else []
+        return self.bootstrap_decorate(self.render_input(self.converter.convert_to_form(value), error))
 
     def parse(self, data):
-        return {self.id: self.converter.convert_from_form(data[self.id][0])} if self.id in data else {}
+        value = self.converter.convert_from_form(data[self.id][0])
+        if self.validator is not None:
+            self.validator.validate(self.id, value)
+        return {self.id: value} if self.id in data else {}
 
     def getLabel(self):
         return self.label
 
 
 class TextInput(Input):
-    def input_properties(self, value):
-        props = super().input_properties(value)
+    def input_properties(self, value, errors):
+        props = super().input_properties(value, errors)
         props["type"] = "text"
         return props
 
@@ -95,14 +108,14 @@ class NumberInput(Input):
     def defaultConverter(self):
         return IntConverter()
 
-    def input_properties(self, value):
-        props = super().input_properties(value)
+    def input_properties(self, value, errors):
+        props = super().input_properties(value, errors)
         props["type"] = "number"
         if self.step:
             props["step"] = self.step
         return props
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
         if self.append:
             append = """
                 <div class="input-group-append">
@@ -120,7 +133,7 @@ class NumberInput(Input):
                 {append}
             </div>
         """.format(
-            input=super().render_input(value),
+            input=super().render_input(value, errors),
             append=append,
         )
 
@@ -135,7 +148,8 @@ class FloatInput(NumberInput):
 
 
 class LocationInput(Input):
-    def render_input(self, value):
+    def render_input(self, value, errors):
+        # TODO display errors
         return """
             <div class="row">
                 {inputs}
@@ -145,11 +159,11 @@ class LocationInput(Input):
             </div>
         """.format(
             id=self.id,
-            inputs="".join(self.render_sub_input(value, id) for id in ["lat", "lon"]),
+            inputs="".join(self.render_sub_input(value, id, errors) for id in ["lat", "lon"]),
             key=Config.get()["google_maps_api_key"],
         )
 
-    def render_sub_input(self, value, id):
+    def render_sub_input(self, value, id, errors):
         return """
             <div class="col">
                 <input type="number" class="{classes}" id="{id}" name="{id}" placeholder="{label}" value="{value}"
@@ -158,7 +172,7 @@ class LocationInput(Input):
         """.format(
             id="{0}-{1}".format(self.id, id),
             label=self.label,
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             value=value[id],
             disabled="disabled" if self.disabled else "",
         )
@@ -168,11 +182,16 @@ class LocationInput(Input):
 
 
 class TextAreaInput(Input):
-    def render_input(self, value):
+    def render_input(self, value, errors):
         return """
             <textarea class="{classes}" id="{id}" name="{id}" style="height:200px;" {disabled}>{value}</textarea>
+            {errors}
         """.format(
-            id=self.id, classes=self.input_classes(), value=value, disabled="disabled" if self.disabled else ""
+            id=self.id,
+            classes=self.input_classes(errors),
+            value=value,
+            disabled="disabled" if self.disabled else "",
+            errors=self.render_errors(errors),
         )
 
 
@@ -181,7 +200,7 @@ class CheckboxInput(Input):
         super().__init__(id, "", infotext=infotext, converter=converter)
         self.checkboxText = checkboxText
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
         return """
             <div class="{classes}">
                 <input type="hidden" name="{id}" value="0" {disabled}>
@@ -189,17 +208,22 @@ class CheckboxInput(Input):
                 <label class="form-check-label" for="{id}">
                     {checkboxText}
                 </label>
+                {errors}
             </div>
         """.format(
             id=self.id,
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             checked="checked" if value else "",
             disabled="disabled" if self.disabled else "",
             checkboxText=self.checkboxText,
+            errors=self.render_errors(errors)
         )
 
-    def input_classes(self):
-        return " ".join(["form-check", "form-control-sm"])
+    def input_classes(self, error):
+        classes = ["form-check", "form-control-sm"]
+        if error:
+            classes.append("is-invalid")
+        return " ".join(classes)
 
     def parse(self, data):
         if self.id in data:
@@ -222,13 +246,14 @@ class MultiCheckboxInput(Input):
         super().__init__(id, label, infotext=infotext)
         self.options = options
 
-    def render_input(self, value):
-        return "".join(self.render_checkbox(o, value) for o in self.options)
+    def render_input(self, value, errors):
+        # TODO display errors
+        return "".join(self.render_checkbox(o, value, errors) for o in self.options)
 
     def checkbox_id(self, option):
         return "{0}-{1}".format(self.id, option.value)
 
-    def render_checkbox(self, option, value):
+    def render_checkbox(self, option, value, errors):
         return """
           <div class="{classes}">
             <input class="form-check-input" type="checkbox" id="{id}" name="{id}" {checked} {disabled}>
@@ -238,7 +263,7 @@ class MultiCheckboxInput(Input):
           </div>
         """.format(
             id=self.checkbox_id(option),
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             checked="checked" if option.value in value else "",
             checkboxText=option.text,
             disabled="disabled" if self.disabled else "",
@@ -251,8 +276,11 @@ class MultiCheckboxInput(Input):
 
         return {self.id: [o.value for o in self.options if in_response(o)]}
 
-    def input_classes(self):
-        return " ".join(["form-check", "form-control-sm"])
+    def input_classes(self, error):
+        classes = ["form-check", "form-control-sm"]
+        if error:
+            classes.append("is-invalid")
+        return " ".join(classes)
 
 
 class ServicesCheckboxInput(MultiCheckboxInput):
@@ -286,14 +314,16 @@ class DropdownInput(Input):
             self.options = options
         super().__init__(id, label, infotext=infotext, converter=converter)
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
         return """
             <select class="{classes}" id="{id}" name="{id}" {disabled}>{options}</select>
+            {errors}
         """.format(
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             id=self.id,
             options=self.render_options(value),
             disabled="disabled" if self.disabled else "",
+            errors=self.render_errors(errors),
         )
 
     def render_options(self, value):
@@ -329,13 +359,13 @@ class ExponentialInput(Input):
     def defaultConverter(self):
         return IntConverter()
 
-    def input_properties(self, value):
-        props = super().input_properties(value)
+    def input_properties(self, value, errors):
+        props = super().input_properties(value, errors)
         props["type"] = "number"
         props["step"] = "any"
         return props
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
         append = """
             <div class="input-group-append">
                 <select class="input-group-text exponent" name="{id}-exponent" {disabled}>
@@ -358,7 +388,7 @@ class ExponentialInput(Input):
                 {append}
             </div>
         """.format(
-            input=super().render_input(value),
+            input=super().render_input(value, errors),
             append=append,
         )
 
diff --git a/owrx/form/device.py b/owrx/form/device.py
index 767a010..0d19875 100644
--- a/owrx/form/device.py
+++ b/owrx/form/device.py
@@ -10,7 +10,8 @@ class GainInput(Input):
         self.has_agc = has_agc
         self.gain_stages = gain_stages
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
+        # TODO display errors
         try:
             display_value = float(value)
         except (ValueError, TypeError):
@@ -29,11 +30,11 @@ class GainInput(Input):
             </div>
         """.format(
             id=self.id,
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             value=display_value,
             label=self.label,
             options=self.render_options(value),
-            stageoption="" if self.gain_stages is None else self.render_stage_option(value),
+            stageoption="" if self.gain_stages is None else self.render_stage_option(value, errors),
             disabled="disabled" if self.disabled else "",
         )
 
@@ -71,7 +72,7 @@ class GainInput(Input):
 
         return "stages"
 
-    def render_stage_option(self, value):
+    def render_stage_option(self, value, errors):
         try:
             value_dict = {k: v for item in SoapySettings.parse(value) for k, v in item.items()}
         except (AttributeError, ValueError):
@@ -93,7 +94,7 @@ class GainInput(Input):
                     id=self.id,
                     stage=stage,
                     value=value_dict[stage] if stage in value_dict else "",
-                    classes=self.input_classes(),
+                    classes=self.input_classes(errors),
                     disabled="disabled" if self.disabled else "",
                 )
                 for stage in self.gain_stages
@@ -172,12 +173,12 @@ class SchedulerInput(Input):
         super().__init__(id, label)
         self.profiles = {}
 
-    def render(self, config):
+    def render(self, config, errors):
         if "profiles" in config:
             self.profiles = config["profiles"]
-        return super().render(config)
+        return super().render(config, errors)
 
-    def render_profiles_select(self, value, config_key, stage, extra_classes=""):
+    def render_profiles_select(self, value, errors, config_key, stage, extra_classes=""):
         stage_value = ""
         if value and "schedule" in value and config_key in value["schedule"]:
             stage_value = value["schedule"][config_key]
@@ -188,7 +189,7 @@ class SchedulerInput(Input):
             </select> 
         """.format(
             id="{}-{}".format(self.id, stage),
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             extra_classes=extra_classes,
             disabled="disabled" if self.disabled else "",
             options="".join(
@@ -203,7 +204,7 @@ class SchedulerInput(Input):
             ),
         )
 
-    def render_static_entires(self, value):
+    def render_static_entires(self, value, errors):
         def render_time_inputs(v):
             values = ["{}:{}".format(x[0:2], x[2:4]) for x in [v[0:4], v[5:9]]]
             return '<div class="p-1">-</div>'.join(
@@ -211,7 +212,7 @@ class SchedulerInput(Input):
                     <input type="time" class="{classes}" id="{id}" name="{id}" {disabled} value="{value}">
                 """.format(
                     id="{}-{}-{}".format(self.id, "time", "start" if i == 0 else "end"),
-                    classes=self.input_classes(),
+                    classes=self.input_classes(errors),
                     disabled="disabled" if self.disabled else "",
                     value=v,
                 )
@@ -231,7 +232,7 @@ class SchedulerInput(Input):
                 </div>
             """.format(
                 time_inputs=render_time_inputs(slot),
-                select=self.render_profiles_select(value, slot, "profile"),
+                select=self.render_profiles_select(value, errors, slot, "profile"),
             )
             for slot, entry in schedule.items()
         )
@@ -249,10 +250,10 @@ class SchedulerInput(Input):
         """.format(
             rows=rows,
             time_inputs=render_time_inputs("0000-0000"),
-            select=self.render_profiles_select("", "0000-0000", "profile"),
+            select=self.render_profiles_select("", errors, "0000-0000", "profile"),
         )
 
-    def render_daylight_entries(self, value):
+    def render_daylight_entries(self, value, errors):
         return "".join(
             """
                 <div class="row">
@@ -261,12 +262,12 @@ class SchedulerInput(Input):
                 </div>
             """.format(
                 name=name,
-                select=self.render_profiles_select(value, stage, stage, extra_classes="col-9"),
+                select=self.render_profiles_select(value, errors, stage, stage, extra_classes="col-9"),
             )
             for stage, name in [("day", "Day"), ("night", "Night"), ("greyline", "Greyline")]
         )
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
         return """
             <div id="{id}">
                 <select class="{classes} mode" id="{id}-select" name="{id}-select" {disabled}>
@@ -281,11 +282,11 @@ class SchedulerInput(Input):
             </div>
         """.format(
             id=self.id,
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             disabled="disabled" if self.disabled else "",
             options=self.render_options(value),
-            entries=self.render_static_entires(value),
-            stages=self.render_daylight_entries(value),
+            entries=self.render_static_entires(value, errors),
+            stages=self.render_daylight_entries(value, errors),
         )
 
     def _get_mode(self, value):
@@ -341,7 +342,8 @@ class SchedulerInput(Input):
 
 
 class WaterfallLevelsInput(Input):
-    def render_input(self, value):
+    def render_input(self, value, errors):
+        # TODO display errors
         return """
             <div class="row" id="{id}">
                 {inputs}
@@ -364,7 +366,7 @@ class WaterfallLevelsInput(Input):
                     name=name,
                     label=label,
                     value=value[name] if value and name in value else "0",
-                    classes=self.input_classes(),
+                    classes=self.input_classes(errors),
                     disabled="disabled" if self.disabled else "",
                 )
                 for name, label in [("min", "Minimum"), ("max", "Maximum")]
diff --git a/owrx/form/error.py b/owrx/form/error.py
new file mode 100644
index 0000000..60eef10
--- /dev/null
+++ b/owrx/form/error.py
@@ -0,0 +1,15 @@
+class FormError(Exception):
+    def __init__(self, key, message):
+        super().__init__("Error processing form data for {}: {}".format(key, message))
+        self.key = key
+        self.message = message
+
+    def getKey(self):
+        return self.key
+
+    def getMessage(self):
+        return self.message
+
+
+class ValidationError(FormError):
+    pass
diff --git a/owrx/form/gfx.py b/owrx/form/gfx.py
index c4d766d..09d63b0 100644
--- a/owrx/form/gfx.py
+++ b/owrx/form/gfx.py
@@ -4,7 +4,8 @@ from datetime import datetime
 
 
 class ImageInput(Input, metaclass=ABCMeta):
-    def render_input(self, value):
+    def render_input(self, value, errors):
+        # TODO display errors
         return """
             <div class="imageupload">
                 <input type="hidden" id="{id}" name="{id}">
diff --git a/owrx/form/validator.py b/owrx/form/validator.py
new file mode 100644
index 0000000..165471f
--- /dev/null
+++ b/owrx/form/validator.py
@@ -0,0 +1,14 @@
+from abc import ABC, abstractmethod
+from owrx.form.error import ValidationError
+
+
+class Validator(ABC):
+    @abstractmethod
+    def validate(self, key, value):
+        pass
+
+
+class RequiredValidator(Validator):
+    def validate(self, key, value):
+        if value is None or value == "":
+            raise ValidationError(key, "Field is required")
diff --git a/owrx/form/wsjt.py b/owrx/form/wsjt.py
index 215b1b7..6fa7302 100644
--- a/owrx/form/wsjt.py
+++ b/owrx/form/wsjt.py
@@ -9,7 +9,7 @@ class Q65ModeMatrix(Input):
     def checkbox_id(self, mode, interval):
         return "{0}-{1}-{2}".format(self.id, mode.value, interval.value)
 
-    def render_checkbox(self, mode: Q65Mode, interval: Q65Interval, value):
+    def render_checkbox(self, mode: Q65Mode, interval: Q65Interval, value, errors):
         return """
             <div class="{classes}">
                 <input class="form-check-input" type="checkbox" id="{id}" name="{id}" {checked} {disabled}>
@@ -18,16 +18,16 @@ class Q65ModeMatrix(Input):
                 </label>
             </div>
         """.format(
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             id=self.checkbox_id(mode, interval),
             checked="checked" if "{}{}".format(mode.name, interval.value) in value else "",
             checkboxText="Mode {} interval {}s".format(mode.name, interval.value),
             disabled="" if interval.is_available(mode) and not self.disabled else "disabled",
         )
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
         checkboxes = "".join(
-            self.render_checkbox(mode, interval, value) for interval in Q65Interval for mode in Q65Mode
+            self.render_checkbox(mode, interval, value, errors) for interval in Q65Interval for mode in Q65Mode
         )
         return """
             <div class="matrix q65-matrix">
@@ -37,8 +37,11 @@ class Q65ModeMatrix(Input):
             checkboxes=checkboxes
         )
 
-    def input_classes(self):
-        return " ".join(["form-check", "form-control-sm"])
+    def input_classes(self, error):
+        classes = ["form-check", "form-control-sm"]
+        if error:
+            classes.append("is-invalid")
+        return " ".join(classes)
 
     def parse(self, data):
         def in_response(mode, interval):
@@ -59,7 +62,7 @@ class WsjtDecodingDepthsInput(Input):
     def defaultConverter(self):
         return JsonConverter()
 
-    def render_input(self, value):
+    def render_input(self, value, errors):
         def render_mode(m):
             return """
                 <option value={mode}>{name}</option>
@@ -76,11 +79,11 @@ class WsjtDecodingDepthsInput(Input):
             </div>
         """.format(
             id=self.id,
-            classes=self.input_classes(),
+            classes=self.input_classes(errors),
             value=html.escape(value),
             options="".join(render_mode(m) for m in Modes.getAvailableModes() if isinstance(m, WsjtMode)),
             disabled="disabled" if self.disabled else ""
         )
 
-    def input_classes(self):
-        return super().input_classes() + " wsjt-decoding-depths"
+    def input_classes(self, error):
+        return super().input_classes(error) + " wsjt-decoding-depths"
diff --git a/owrx/source/__init__.py b/owrx/source/__init__.py
index ef9f4e4..a5fb7db 100644
--- a/owrx/source/__init__.py
+++ b/owrx/source/__init__.py
@@ -488,19 +488,23 @@ class OptionalSection(Section):
             )
         )
 
-    def render_optional_inputs(self, data):
+    def render_optional_inputs(self, data, errors):
         return """
             <div class="optional-inputs" style="display: none;">
                 {inputs}
             </div>
         """.format(
-            inputs="".join(self.render_input(input, data) for input in self.optional_inputs)
+            inputs="".join(self.render_input(input, data, errors) for input in self.optional_inputs)
         )
 
-    def render_inputs(self, data):
-        return super().render_inputs(data) + self.render_optional_select() + self.render_optional_inputs(data)
+    def render_inputs(self, data, errors):
+        return (
+            super().render_inputs(data, errors)
+            + self.render_optional_select()
+            + self.render_optional_inputs(data, errors)
+        )
 
-    def render(self, data):
+    def render(self, data, errors):
         indexed_inputs = {input.id: input for input in self.inputs}
         visible_keys = set(self.mandatory + [k for k in self.optional if k in data])
         optional_keys = set(k for k in self.optional if k not in data)
@@ -512,15 +516,15 @@ class OptionalSection(Section):
         for input in self.optional_inputs:
             input.setRemovable()
             input.setDisabled()
-        return super().render(data)
+        return super().render(data, errors)
 
     def parse(self, data):
-        data = super().parse(data)
+        data, errors = super().parse(data)
         # remove optional keys if they have been removed from the form
         for k in self.optional:
             if k not in data:
                 data[k] = None
-        return data
+        return data, errors
 
 
 class SdrDeviceDescription(object):
@@ -542,6 +546,7 @@ class SdrDeviceDescription(object):
                 return True
             except SdrDeviceDescriptionMissing:
                 return False
+
         return [module_name for _, module_name, _ in pkgutil.walk_packages(__path__) if has_description(module_name)]
 
     def getDeviceInputs(self) -> List[Input]: