diff --git a/src/controllers/form.ts b/src/controllers/form.ts
index 10fe5ac..d568272 100644
--- a/src/controllers/form.ts
+++ b/src/controllers/form.ts
@@ -23,7 +23,20 @@ import {
   getDBForm,
   getDBFormsByUser,
   submitDBAnswer,
+  getDBFormQuestions,
 } from '../db'
+import {
+  validateCreateFormParameters,
+  validateSubmitAnswerParameters,
+} from './validate'
+
+const formatQuestions = (
+  choisesQuestions: (ChoisesQuestion & {
+    variants: Variant[]
+  })[],
+  inputQuestions: InputQuestion[]
+) =>
+  [...choisesQuestions, ...inputQuestions].sort((a, b) => a.number - b.number)
 
 const getForm = async (
   db: PrismaClient,
@@ -39,15 +52,19 @@ const getForm = async (
       author: dbForm.author,
       dateCreated: dbForm.dateCreated.toString(),
       id: dbForm.id,
-      questions: [...dbForm.choisesQuestions, ...dbForm.inputQuestions].sort(
-        (a, b) => a.number - b.number
+      questions: formatQuestions(
+        dbForm.choisesQuestions,
+        dbForm.inputQuestions
       ),
-      submissions: dbForm.submissions.map((submission) => ({
-        user: submission.user,
-        answers: submission.answers,
-        date: submission.date.toString(),
-        id: submission.id,
-      })),
+      submissions:
+        dbForm.submissions.length == 0
+          ? null
+          : dbForm.submissions.map((submission) => ({
+              user: submission.user,
+              answers: submission.answers,
+              date: submission.date.toString(),
+              id: submission.id,
+            })),
       title: dbForm.title,
     }
 
@@ -93,6 +110,8 @@ const createFormFrom = async (
   try {
     const parsedQuestions = <UploadedQuestion[]>JSON.parse(params.questions)
 
+    await validateCreateFormParameters(params.title, parsedQuestions)
+
     const newForm: FormConstructor = {
       choisesQuestions: {
         create: parsedQuestions.flatMap<CreateChoises>(
@@ -139,9 +158,22 @@ const submitAnswer = async (
   userId: number
 ): Promise<ServerAnswer> => {
   try {
+    const form = await getDBFormQuestions(db, formId)
+    if (!form) throw new UserInputError("Can't submit form")
+
+    console.log(formatQuestions(form.choisesQuestions, form.inputQuestions))
+
+    form.submissions.forEach((submission) => {
+      if (submission.userId === userId)
+        throw new UserInputError("Can't submit same form more than once")
+    })
+
     const parsedAnswers = <DbAnswer[]>JSON.parse(answers)
 
-    console.log(parsedAnswers)
+    await validateSubmitAnswerParameters(
+      parsedAnswers,
+      formatQuestions(form.choisesQuestions, form.inputQuestions)
+    )
 
     const res = await submitDBAnswer(db, userId, formId, parsedAnswers)
 
@@ -165,9 +197,7 @@ const formatForms = (
   forms.map<GraphqlForm>((form) => ({
     dateCreated: form.dateCreated.toString(),
     id: form.id,
-    questions: [...form.choisesQuestions, ...form.inputQuestions].sort(
-      (a, b) => a.number - b.number
-    ),
+    questions: formatQuestions(form.choisesQuestions, form.inputQuestions),
     submissions: form.submissions.map((submission) => ({
       answers: submission.answers,
       date: submission.date.toString(),
diff --git a/src/controllers/validate.ts b/src/controllers/validate.ts
new file mode 100644
index 0000000..b65ed5a
--- /dev/null
+++ b/src/controllers/validate.ts
@@ -0,0 +1,127 @@
+'use strict'
+import { UserInputError } from 'apollo-server-express'
+import { Answer } from '@prisma/client'
+import {
+  UploadedChoisesQuestion,
+  UploadedInputQuestion,
+  UploadedQuestion,
+} from './types'
+import { ChoisesQuestion, InputQuestion, Variant } from 'typeDefs/typeDefs.gen'
+
+const choisesVariants = ['CHECK', 'CHOOSE', 'SELECT']
+
+const validateCreateFormParameters = async (
+  title: string,
+  questions: UploadedQuestion[]
+) => {
+  if (!title)
+    throw new UserInputError("Form title can't be empty", {
+      invalidArgs: ['title'],
+    })
+
+  questions.forEach(
+    (question: UploadedChoisesQuestion | UploadedInputQuestion) => {
+      if (!question.title)
+        throw new UserInputError("Question title can't be empty", {
+          invalidArgs: ['questions'],
+        })
+
+      if ('type' in question) {
+        if (!question.variants || question.variants.length < 1)
+          throw new UserInputError(
+            'Question with choises must have at least one answer variant',
+            { invalidArgs: ['questions'] }
+          )
+
+        question.variants.forEach((variant) => {
+          if (!variant.text || variant.text.length < 1)
+            throw new UserInputError("Choises variant text can't be empty", {
+              invalidArgs: ['questions'],
+            })
+        })
+
+        if (!choisesVariants.includes(question.type))
+          throw new UserInputError(
+            'Question with choises must be of one of supported types',
+            { invalidArgs: ['questions'] }
+          )
+      }
+    }
+  )
+}
+
+const validateSubmitAnswerParameters = async (
+  answers: Answer[],
+  questions: (
+    | (ChoisesQuestion & {
+        variants: Variant[]
+      })
+    | InputQuestion
+  )[]
+) => {
+  questions.forEach((question, questionIndex) => {
+    const answer = answers[questionIndex]
+
+    if (!answer)
+      throw new UserInputError('Every required question must have answer', {
+        invalidArgs: ['answers'],
+      })
+
+    if (!answer.type)
+      throw new UserInputError('Type must be specified for answer', {
+        invalidArgs: ['answers'],
+      })
+
+    if (answer.type !== 'CHOISE' && answer.type !== 'INPUT')
+      throw new UserInputError('Answer must have supported type', {
+        invalidArgs: ['answers'],
+      })
+
+    if (answer.type === 'CHOISE' && !('type' in question))
+      throw new UserInputError(
+        `Answer ${questionIndex + 1} must be of 'INPUT' type`,
+        {
+          invalidArgs: ['answers'],
+        }
+      )
+
+    if (answer.type === 'INPUT' && 'type' in question)
+      throw new UserInputError(
+        `Answer ${questionIndex + 1} must be of 'CHOISE' type`,
+        {
+          invalidArgs: ['answers'],
+        }
+      )
+
+    if (answer.type === 'CHOISE' && answer.userChoise === null)
+      throw new UserInputError(
+        "Question of type 'CHOISE' must have choise number set",
+        {
+          invalidArgs: ['answers'],
+        }
+      )
+
+    if (answer.type === 'INPUT' && answer.userInput === null)
+      throw new UserInputError(
+        "Question of type 'INPUT' must have input string",
+        {
+          invalidArgs: ['answers'],
+        }
+      )
+
+    if (
+      answer.userChoise !== null &&
+      (question as ChoisesQuestion).variants &&
+      answer.userChoise > (question as ChoisesQuestion).variants.length - 1
+    )
+      throw new UserInputError(
+        "Can't have chosen number bigger than amount of variants: " +
+          (question as ChoisesQuestion).variants.length,
+        {
+          invalidArgs: ['answers'],
+        }
+      )
+  })
+}
+
+export { validateCreateFormParameters, validateSubmitAnswerParameters }
diff --git a/src/db/index.ts b/src/db/index.ts
index 5be26b7..a7644c4 100644
--- a/src/db/index.ts
+++ b/src/db/index.ts
@@ -176,6 +176,26 @@ const submitDBAnswer = (
     },
   })
 
+const getDBFormQuestions = async (db: PrismaClient, formId: number) =>
+  db.form.findOne({
+    where: {
+      id: formId,
+    },
+    select: {
+      choisesQuestions: {
+        include: {
+          variants: true,
+        },
+      },
+      inputQuestions: true,
+      submissions: {
+        select: {
+          userId: true,
+        },
+      },
+    },
+  })
+
 export {
   createDBForm,
   createDBUser,
@@ -184,4 +204,5 @@ export {
   getDBFormAuthor,
   getDBFormsByUser,
   submitDBAnswer,
+  getDBFormQuestions,
 }