diff --git a/go.mod b/go.mod
index cab4662..0440e90 100644
--- a/go.mod
+++ b/go.mod
@@ -5,17 +5,23 @@ go 1.24.1
 require (
 	github.com/Tnze/go-mc v1.20.2
 	github.com/go-chi/chi/v5 v5.2.1
+	github.com/go-playground/validator/v10 v10.30.1
 	github.com/golang-jwt/jwt/v5 v5.2.2
 	github.com/google/uuid v1.6.0
 	github.com/gorilla/websocket v1.5.3
 	github.com/jackc/pgx/v5 v5.7.5
-	golang.org/x/crypto v0.39.0
+	golang.org/x/crypto v0.46.0
 )
 
 require (
+	github.com/gabriel-vasile/mimetype v1.4.12 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
-	golang.org/x/sync v0.15.0 // indirect
-	golang.org/x/text v0.26.0 // indirect
+	github.com/leodido/go-urn v1.4.0 // indirect
+	golang.org/x/sync v0.19.0 // indirect
+	golang.org/x/sys v0.39.0 // indirect
+	golang.org/x/text v0.32.0 // indirect
 )
diff --git a/go.sum b/go.sum
index 8cfb9de..4252793 100644
--- a/go.sum
+++ b/go.sum
@@ -3,8 +3,18 @@ github.com/Tnze/go-mc v1.20.2/go.mod h1:geoRj2HsXSkB3FJBuhr7wCzXegRlzWsVXd7h7jiJ
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gabriel-vasile/mimetype v1.4.12 h1:e9hWvmLYvtp846tLHam2o++qitpguFiYCKbn0w9jyqw=
+github.com/gabriel-vasile/mimetype v1.4.12/go.mod h1:d+9Oxyo1wTzWdyVUPMmXFvp4F9tea18J8ufA774AB3s=
 github.com/go-chi/chi/v5 v5.2.1 h1:KOIHODQj58PmL80G2Eak4WdvUzjSJSm0vG72crDCqb8=
 github.com/go-chi/chi/v5 v5.2.1/go.mod h1:L2yAIGWB3H+phAw1NxKwWM+7eUH/lU8pOMm5hHcoops=
+github.com/go-playground/assert/v2 v2.2.0 h1:JvknZsQTYeFEAhQwI4qEt9cyV5ONwRHC+lYKSsYSR8s=
+github.com/go-playground/assert/v2 v2.2.0/go.mod h1:VDjEfimB/XKnb+ZQfWdccd7VUvScMdVu0Titje2rxJ4=
+github.com/go-playground/locales v0.14.1 h1:EWaQ/wswjilfKLTECiXz7Rh+3BjFhfDFKv/oXslEjJA=
+github.com/go-playground/locales v0.14.1/go.mod h1:hxrqLVvrK65+Rwrd5Fc6F2O76J/NuW9t0sjnWqG1slY=
+github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJnYK9S473LQFuzCbDbfSFY=
+github.com/go-playground/universal-translator v0.18.1/go.mod h1:xekY+UJKNuX9WP91TpwSH2VMlDf28Uj24BCp08ZFTUY=
+github.com/go-playground/validator/v10 v10.30.1 h1:f3zDSN/zOma+w6+1Wswgd9fLkdwy06ntQJp0BBvFG0w=
+github.com/go-playground/validator/v10 v10.30.1/go.mod h1:oSuBIQzuJxL//3MelwSLD5hc2Tu889bF0Idm9Dg26cM=
 github.com/golang-jwt/jwt/v5 v5.2.2 h1:Rl4B7itRWVtYIHFrSNd7vhTiz9UpLdi6gZhZ3wEeDy8=
 github.com/golang-jwt/jwt/v5 v5.2.2/go.mod h1:pqrtFR0X4osieyHYxtmOUWsAWrfe1Q5UVIyoH402zdk=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
@@ -19,19 +29,23 @@ github.com/jackc/pgx/v5 v5.7.5 h1:JHGfMnQY+IEtGM63d+NGMjoRpysB2JBwDr5fsngwmJs=
 github.com/jackc/pgx/v5 v5.7.5/go.mod h1:aruU7o91Tc2q2cFp5h4uP3f6ztExVpyVv88Xl/8Vl8M=
 github.com/jackc/puddle/v2 v2.2.2 h1:PR8nw+E/1w0GLuRFSmiioY6UooMp6KJv0/61nB7icHo=
 github.com/jackc/puddle/v2 v2.2.2/go.mod h1:vriiEXHvEE654aYKXXjOvZM39qJ0q+azkZFrfEOc3H4=
+github.com/leodido/go-urn v1.4.0 h1:WT9HwE9SGECu3lg4d/dIA+jxlljEa1/ffXKmRjqdmIQ=
+github.com/leodido/go-urn v1.4.0/go.mod h1:bvxc+MVxLKB4z00jd1z+Dvzr47oO32F/QSNjSBOlFxI=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
-github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
-github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
-golang.org/x/crypto v0.39.0 h1:SHs+kF4LP+f+p14esP5jAoDpHU8Gu/v9lFRK6IT5imM=
-golang.org/x/crypto v0.39.0/go.mod h1:L+Xg3Wf6HoL4Bn4238Z6ft6KfEpN0tJGo53AAPC632U=
-golang.org/x/sync v0.15.0 h1:KWH3jNZsfyT6xfAfKiz6MRNmd46ByHDYaZ7KSkCtdW8=
-golang.org/x/sync v0.15.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
-golang.org/x/text v0.26.0 h1:P42AVeLghgTYr4+xUnTRKDMqpar+PtX7KWuNQL21L8M=
-golang.org/x/text v0.26.0/go.mod h1:QK15LZJUUQVJxhz7wXgxSy/CJaTFjd0G+YLonydOVQA=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+golang.org/x/crypto v0.46.0 h1:cKRW/pmt1pKAfetfu+RCEvjvZkA9RimPbh7bhFjGVBU=
+golang.org/x/crypto v0.46.0/go.mod h1:Evb/oLKmMraqjZ2iQTwDwvCtJkczlDuTmdJXoZVzqU0=
+golang.org/x/sync v0.19.0 h1:vV+1eWNmZ5geRlYjzm2adRgW2/mcpevXNg50YZtPCE4=
+golang.org/x/sync v0.19.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=
+golang.org/x/sys v0.39.0 h1:CvCKL8MeisomCi6qNZ+wbb0DN9E5AATixKsvNtMoMFk=
+golang.org/x/sys v0.39.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
+golang.org/x/text v0.32.0 h1:ZD01bjUt1FQ9WJ0ClOL5vxgxOI/sVCNgX1YtKwcY0mU=
+golang.org/x/text v0.32.0/go.mod h1:o/rUWzghvpD5TXrTIBuJU77MTaN0ljMWE47kxGJQ7jY=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
diff --git a/internal/api/auth_handler.go b/internal/api/auth_handler.go
index 9cb8d10..ad562be 100644
--- a/internal/api/auth_handler.go
+++ b/internal/api/auth_handler.go
@@ -8,6 +8,7 @@ import (
 
 	"gitea.mrixs.me/minecraft-platform/backend/internal/core"
 	"gitea.mrixs.me/minecraft-platform/backend/internal/models"
+	"gitea.mrixs.me/minecraft-platform/backend/internal/utils"
 )
 
 type AuthHandler struct {
@@ -27,6 +28,13 @@ func (h *AuthHandler) Authenticate(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if validationErrors := utils.ValidateStruct(req); validationErrors != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		json.NewEncoder(w).Encode(validationErrors)
+		return
+	}
+
 	response, err := h.Service.Authenticate(r.Context(), req)
 	if err != nil {
 		if errors.Is(err, core.ErrInvalidCredentials) {
@@ -57,6 +65,13 @@ func (h *AuthHandler) Join(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if validationErrors := utils.ValidateStruct(req); validationErrors != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		json.NewEncoder(w).Encode(validationErrors)
+		return
+	}
+
 	err := h.Service.ValidateJoinRequest(r.Context(), req)
 	if err != nil {
 		if errors.Is(err, core.ErrInvalidCredentials) {
@@ -84,6 +99,13 @@ func (h *AuthHandler) Login(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if validationErrors := utils.ValidateStruct(req); validationErrors != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		json.NewEncoder(w).Encode(validationErrors)
+		return
+	}
+
 	token, user, err := h.Service.LoginUser(r.Context(), req)
 	if err != nil {
 		if errors.Is(err, core.ErrInvalidCredentials) {
diff --git a/internal/api/user_handler.go b/internal/api/user_handler.go
index 8ecb9aa..b1482bf 100644
--- a/internal/api/user_handler.go
+++ b/internal/api/user_handler.go
@@ -4,11 +4,13 @@ import (
 	"encoding/json"
 	"errors"
 	"log"
+	"log/slog"
 	"net/http"
 
 	"gitea.mrixs.me/minecraft-platform/backend/internal/core"
 	"gitea.mrixs.me/minecraft-platform/backend/internal/database"
 	"gitea.mrixs.me/minecraft-platform/backend/internal/models"
+	"gitea.mrixs.me/minecraft-platform/backend/internal/utils"
 	"github.com/golang-jwt/jwt/v5"
 )
 
@@ -23,13 +25,18 @@ func (h *UserHandler) Register(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// --- ДОБАВЛЕНО ЛОГИРОВАНИЕ ---
-	log.Printf("[Handler] Received registration request for username: '%s', email: '%s'", req.Username, req.Email)
+	if validationErrors := utils.ValidateStruct(req); validationErrors != nil {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusBadRequest)
+		json.NewEncoder(w).Encode(validationErrors)
+		return
+	}
+
+	slog.Info("Received registration request", "username", req.Username, "email", req.Email)
 
 	err := h.Service.RegisterNewUser(r.Context(), req)
 	if err != nil {
-		// --- ДОБАВЛЕНО ЛОГИРОВАНИЕ ОШИБКИ ---
-		log.Printf("[Handler] Service returned error: %v", err)
+		slog.Error("Service returned error", "error", err)
 
 		switch {
 		case errors.Is(err, database.ErrUserExists):
@@ -42,8 +49,7 @@ func (h *UserHandler) Register(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// --- ДОБАВЛЕНО ЛОГИРОВАНИЕ УСПЕХА ---
-	log.Printf("[Handler] User '%s' registered successfully.", req.Username)
+	slog.Info("User registered successfully", "username", req.Username)
 	w.WriteHeader(http.StatusCreated)
 }
 
diff --git a/internal/models/auth.go b/internal/models/auth.go
index 0673f5d..6af3901 100644
--- a/internal/models/auth.go
+++ b/internal/models/auth.go
@@ -9,8 +9,8 @@ type Agent struct {
 // AuthenticateRequest - это тело запроса на /authserver/authenticate
 type AuthenticateRequest struct {
 	Agent       Agent  `json:"agent"`
-	Username    string `json:"username"`
-	Password    string `json:"password"`
+	Username    string `json:"username" validate:"required"`
+	Password    string `json:"password" validate:"required"`
 	ClientToken string `json:"clientToken"`
 }
 
@@ -70,15 +70,15 @@ type SessionProfileResponse struct {
 
 // JoinRequest - это тело запроса на /sessionserver/session/minecraft/join
 type JoinRequest struct {
-	AccessToken     string `json:"accessToken"`
-	SelectedProfile string `json:"selectedProfile"` // UUID пользователя без дефисов
-	ServerID        string `json:"serverId"`
+	AccessToken     string `json:"accessToken" validate:"required"`
+	SelectedProfile string `json:"selectedProfile" validate:"required"` // UUID пользователя без дефисов
+	ServerID        string `json:"serverId" validate:"required"`
 }
 
 // LoginRequest - это тело запроса на /api/login
 type LoginRequest struct {
-	Login    string `json:"login"`
-	Password string `json:"password"`
+	Login    string `json:"login" validate:"required"`
+	Password string `json:"password" validate:"required"`
 }
 
 // LoginResponse - это тело успешного ответа с JWT
diff --git a/internal/models/user.go b/internal/models/user.go
index 0585530..3e41b10 100644
--- a/internal/models/user.go
+++ b/internal/models/user.go
@@ -20,9 +20,9 @@ type User struct {
 
 // RegisterRequest определяет структуру JSON-запроса на регистрацию
 type RegisterRequest struct {
-	Username string `json:"username"`
-	Email    string `json:"email"`
-	Password string `json:"password"`
+	Username string `json:"username" validate:"required,min=3,max=16,alphanum"`
+	Email    string `json:"email" validate:"required,email"`
+	Password string `json:"password" validate:"required,min=8"`
 }
 type Profile struct {
 	ID        int       `json:"-"`
diff --git a/internal/utils/validator.go b/internal/utils/validator.go
new file mode 100644
index 0000000..1f640ba
--- /dev/null
+++ b/internal/utils/validator.go
@@ -0,0 +1,47 @@
+package utils
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/go-playground/validator/v10"
+)
+
+var validate *validator.Validate
+
+func init() {
+	validate = validator.New()
+}
+
+// ValidationErrorResponse represents the structure of validation errors returned to the client
+type ValidationErrorResponse struct {
+	Errors map[string]string `json:"errors"`
+}
+
+// ValidateStruct validates a struct based on its tags using go-playground/validator
+func ValidateStruct(s interface{}) *ValidationErrorResponse {
+	err := validate.Struct(s)
+	if err != nil {
+		var errorsMap = make(map[string]string)
+		for _, err := range err.(validator.ValidationErrors) {
+			// Simpler error messages for now. Can be enhanced with universal-translator.
+			fieldName := strings.ToLower(err.Field())
+			switch err.Tag() {
+			case "required":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' is required", fieldName)
+			case "email":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must be a valid email", fieldName)
+			case "min":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must be at least %s characters long", fieldName, err.Param())
+			case "max":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must be at most %s characters long", fieldName, err.Param())
+			case "alphanum":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must contain only alphanumeric characters", fieldName)
+			default:
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' failed validation on '%s' tag", fieldName, err.Tag())
+			}
+		}
+		return &ValidationErrorResponse{Errors: errorsMap}
+	}
+	return nil
+}