diff --git a/internal/application/application.go b/internal/application/application.go
index 26bcf32..297013d 100644
--- a/internal/application/application.go
+++ b/internal/application/application.go
@@ -14,19 +14,16 @@ import (
 // Application is a thing that responsible for all application-related
 // actions like data fetching, storing, etc. on higher level.
 type Application struct {
-	config   *Config
-	ctx      context.Context
-	doneChan chan struct{}
-	logger   *logger.Logger
-	name     string
-
-	storage     storage.Metrics
-	storageDone chan struct{}
-
-	fetchIsRunning      bool
+	ctx                 context.Context
+	storage             storage.Metrics
+	config              *Config
+	doneChan            chan struct{}
+	logger              *logger.Logger
+	storageDone         chan struct{}
+	httpClient          *http.Client
+	name                string
 	fetchIsRunningMutex sync.RWMutex
-
-	httpClient *http.Client
+	fetchIsRunning      bool
 }
 
 // NewApplication creates new application.
diff --git a/internal/application/config.go b/internal/application/config.go
index ef3f5d4..3843066 100644
--- a/internal/application/config.go
+++ b/internal/application/config.go
@@ -4,11 +4,11 @@ import "time"
 
 // Config is a generic application configuration.
 type Config struct {
+	// Headers is a list of headers that should be added to metrics request.
+	Headers map[string]string `yaml:"headers"`
 	// Endpoint is a remote application endpoint which should give us metrics
 	// in Prometheus format.
 	Endpoint string `yaml:"endpoint"`
-	// Headers is a list of headers that should be added to metrics request.
-	Headers map[string]string `yaml:"headers"`
 	// TimeBetweenRequests is a minimal amount of time which should pass
 	// between requests.
 	TimeBetweenRequests time.Duration `yaml:"time_between_requests"`
diff --git a/internal/application/parser.go b/internal/application/parser.go
index 61b1002..c2ab3af 100644
--- a/internal/application/parser.go
+++ b/internal/application/parser.go
@@ -29,6 +29,7 @@ func (a *Application) parse(body string) map[string]models.Metric {
 		a.logger.Debugln("Analyzing line:", line)
 
 		name = a.getMetricName(line)
+
 		metric, found := data[name]
 		if !found {
 			metric = models.NewMetric(name, "", "", nil)
@@ -53,9 +54,9 @@ func (a *Application) parse(body string) map[string]models.Metric {
 
 			data[name] = metric
 
-			// According to https://github.com/Showmax/prometheus-docs/blob/master/content/docs/instrumenting/exposition_formats.md
-			// HELP and TYPE lines should be printed before actual metric. Do not even
+			// According to docs HELP and TYPE lines should be printed before actual metric. Do not even
 			// report bugs regarding that!
+			// Docs: https://github.com/Showmax/prometheus-docs/blob/master/content/docs/instrumenting/exposition_formats.md
 			continue
 		}
 
@@ -76,12 +77,12 @@ func (a *Application) parse(body string) map[string]models.Metric {
 
 		metric.Value = a.getMetricValue(line)
 
-		a.logger.Debugln("Got metric: %+v\n", metric)
+		a.logger.Debugf("Got metric: %+v\n", metric)
 
 		data[name] = metric
 	}
 
-	a.logger.Debugln("Data parsed: %+v\n", data)
+	a.logger.Debugf("Data parsed: %+v\n", data)
 
 	return data
 }
@@ -138,7 +139,7 @@ func (a *Application) getParametersForPrometheusMetric(line string) []string {
 		}
 
 		// Sometimes nestif causes questions, like here. Is code below is
-		// "deply nested"? I think not. So:
+		// "deeply nested"? I think not. So:
 		// nolint:nestif
 		if !paramNameFinished {
 			if string(r) != "=" {
diff --git a/internal/httpserver/handler.go b/internal/httpserver/handler.go
index a54842c..745b1fb 100644
--- a/internal/httpserver/handler.go
+++ b/internal/httpserver/handler.go
@@ -39,7 +39,6 @@ func (h *handler) getAppsList() ([]byte, error) {
 	appsList, err := json.Marshal(apps)
 	if err != nil {
 		// ToDo: log error
-
 		return nil, errNoAppsRegistered
 	}
 
@@ -70,23 +69,41 @@ func (h *handler) getRequestInfo(r *http.Request) (*models.RequestInfo, error) {
 
 	// Parse API version.
 	apiVersionRaw := strings.TrimLeft(pathSplitted[2], "v")
+
 	apiVersion, err := strconv.Atoi(apiVersionRaw)
 	if err != nil {
 		// ToDo: log error
 		return nil, errInvalidAPIVersion
 	}
 
+	// Check used API version.
+	var supportedAPIVersionUsed bool
+
+	for _, version := range supportedAPIVersions {
+		if apiVersion == version {
+			supportedAPIVersionUsed = true
+
+			break
+		}
+	}
+
+	if !supportedAPIVersionUsed {
+		return nil, errInvalidAPIVersion
+	}
+
 	// Get request type and key.
 	requestType = pathSplitted[3]
+
 	if len(pathSplitted) >= 5 {
 		appName = pathSplitted[4]
 	}
+
 	if len(pathSplitted) >= 6 {
 		metricName = strings.Join(pathSplitted[5:], "/")
 	}
 
 	reqInfo := &models.RequestInfo{
-		ApiVersion:  apiVersion,
+		APIVersion:  apiVersion,
 		Application: appName,
 		Metric:      metricName,
 		RequestType: requestType,
@@ -103,8 +120,9 @@ func (h *handler) register(appName string, hndl common.HTTPHandlerFunc) {
 // ServeHTTP handles every HTTP request.
 func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	startTime := time.Now()
+
 	defer func() {
-		requestDuration := time.Now().Sub(startTime)
+		requestDuration := time.Since(startTime)
 
 		log.Printf("[HTTP Request] from %s to %s, duration %.4fs\n", r.RemoteAddr, r.URL.Path, requestDuration.Seconds())
 	}()
diff --git a/internal/models/metric.go b/internal/models/metric.go
index e2598a2..42d45f9 100644
--- a/internal/models/metric.go
+++ b/internal/models/metric.go
@@ -2,16 +2,16 @@ package models
 
 // Metric is a generic metric structure.
 type Metric struct {
-	// Metric name.
+	// Name is a metric name.
 	Name string
-	// HELP data, if present.
+	// Description is a metric description from HELP line.
 	Description string
-	// Additional parameters, data inside "{}".
-	Params []string
-	// Type is a metric type.
+	// Type is a metric type from TYPE line.
 	Type string
-	// Metric value.
+	// Value is a metric value.
 	Value string
+	// Params is an additional params which are placed inside "{}".
+	Params []string
 }
 
 // NewMetric creates new structure for storing single metric data.
@@ -21,6 +21,7 @@ func NewMetric(name, mType, description string, params []string) Metric {
 		Description: description,
 		Type:        mType,
 		Params:      params,
+		Value:       "",
 	}
 
 	return m
diff --git a/internal/models/request_info.go b/internal/models/request_info.go
index b58d8f8..60f796a 100644
--- a/internal/models/request_info.go
+++ b/internal/models/request_info.go
@@ -2,8 +2,8 @@ package models
 
 // RequestInfo is a parsed request information to throw into application's handler.
 type RequestInfo struct {
-	ApiVersion  int
 	Application string
 	Metric      string
 	RequestType string
+	APIVersion  int
 }