diff --git a/src/fiber_package/communication/activity.py b/src/fiber_package/communication/activity.py
index e6f0786..9e9af96 100644
--- a/src/fiber_package/communication/activity.py
+++ b/src/fiber_package/communication/activity.py
@@ -1,5 +1,5 @@
-from typing import Literal, Self
-from pydantic import model_validator
+from typing import Literal, Self, Annotated
+from pydantic import model_validator, Field
 
 from datetime import datetime
 
@@ -8,8 +8,17 @@ from .submodels import ActivityPaymentInfo
 from .enums import CommunicationCategory
 
 from fiber_package.refs import SignupRefList
+from fiber_package.signup.signup import SignupModel
+from fiber_package.signup.util import validate_answer
 
-from fiber_package.signup.elements.form_element import FormElement
+from fiber_package.signup.element.form_base_text import FormBaseText
+from fiber_package.signup.element.form_base_question import FormBaseQuestion
+
+# Special type which uses enum category to decide type!
+FieldUnionType = Annotated[
+    FormBaseText | FormBaseQuestion,
+    Field(discriminator="category")
+]
 
 class ActivityModel(CommunicationModel):
     category: Literal[CommunicationCategory.activity]
@@ -22,7 +31,7 @@ class ActivityModel(CommunicationModel):
 
     payment_info: ActivityPaymentInfo | None = None
 
-    form: list[FormElement]
+    form: list[FieldUnionType]
 
     signups: SignupRefList = SignupRefList([], "signup")
 
@@ -34,3 +43,37 @@ class ActivityModel(CommunicationModel):
         if self.end_time < self.start_time:
             raise ValueError("End time cannot be earlier than start time")
         return self
+
+    def validate_signup_form(self, signup: SignupModel) -> None:
+        required = set()
+        answerable = set()
+
+        question_dict: dict[str, FormBaseQuestion] = {}
+
+        for element in self.form:
+            if isinstance(element, FormBaseText):
+                continue
+            # so we know it is istance of FormBaseQuestion
+            answerable.add(element.name)
+            if element.required:
+                required.add(element.name)
+            question_dict[element.name] = element
+
+        answers = signup.answers
+        for answer in answers:
+            q_name = answer.question_name
+            if q_name not in answerable:
+                raise ValueError(
+                    f"Form contains answer to "
+                    f"non-existing question {q_name}."
+                )
+            answerable.remove(q_name)
+            if answer.question_name in required:
+                required.remove(q_name)
+
+            question = question_dict[q_name]
+            validate_answer(question, answer)
+
+
+        if len(required) > 0:
+            raise ValueError("Form does not answer all required questions.")
diff --git a/src/fiber_package/signup/element/form_base_question.py b/src/fiber_package/signup/element/form_base_question.py
index 11365f0..c0c1942 100644
--- a/src/fiber_package/signup/element/form_base_question.py
+++ b/src/fiber_package/signup/element/form_base_question.py
@@ -1,6 +1,9 @@
 from .form_element import FormElement
+from fiber_package.signup.enums import FormQuestionCategory
 
 class FormBaseQuestion(FormElement):
+    category: FormQuestionCategory
+
     required: bool
 
     title: str | None = None
diff --git a/src/fiber_package/signup/element/form_base_text.py b/src/fiber_package/signup/element/form_base_text.py
new file mode 100644
index 0000000..1cffa93
--- /dev/null
+++ b/src/fiber_package/signup/element/form_base_text.py
@@ -0,0 +1,5 @@
+from .form_element import FormElement
+from fiber_package.signup.enums import FormTextCategory
+
+class FormBaseText(FormElement):
+    category: FormTextCategory
diff --git a/src/fiber_package/signup/element/form_open_questions.py b/src/fiber_package/signup/element/form_open_questions.py
index 8ad5de2..c0429a8 100644
--- a/src/fiber_package/signup/element/form_open_questions.py
+++ b/src/fiber_package/signup/element/form_open_questions.py
@@ -24,7 +24,7 @@ class FormOpenQuestions(FormBaseQuestion):
     def validate_answer(self, answer: AnswerOpenQuestions) -> None:
         if answer.question_name != self.name:
             raise ValueError("Answer question name does not match.")
-        
+
         answer_list = answer.answer_list
         if len(answer_list) != len(self.questions):
             raise ValueError("Length of answer question list does not match.")
diff --git a/src/fiber_package/signup/enums.py b/src/fiber_package/signup/enums.py
index 5455ec8..6dff12b 100644
--- a/src/fiber_package/signup/enums.py
+++ b/src/fiber_package/signup/enums.py
@@ -12,3 +12,8 @@ class FormElementCategory(StrEnum):
 FormQuestionCategory = Literal[
     FormElementCategory.open_questions
 ]
+
+FormTextCategory = Literal[
+    FormElementCategory.text_piece,
+    FormElementCategory.title_text
+]
diff --git a/src/fiber_package/signup/util.py b/src/fiber_package/signup/util.py
new file mode 100644
index 0000000..91d037f
--- /dev/null
+++ b/src/fiber_package/signup/util.py
@@ -0,0 +1,18 @@
+from fiber_package.signup.element.form_base_question import FormBaseQuestion
+from fiber_package.signup.element.form_open_questions import FormOpenQuestions
+
+from fiber_package.signup.answer.answer_base import AnswerBase
+from fiber_package.signup.enums import FormElementCategory
+
+from fiber_package.signup.answer.answer_open_questions import AnswerOpenQuestions
+
+def validate_answer(question: FormBaseQuestion, answer: AnswerBase) -> None:
+    if question.category != answer.category:
+        raise ValueError("Question and answer category do not match!")
+
+    if question.category == FormElementCategory.open_questions:
+        question_val = FormOpenQuestions.model_validate(question.model_dump())
+        answer_val = AnswerOpenQuestions.model_validate(answer.model_dump())
+        question_val.validate_answer(answer_val)
+
+    # TODO: implement