diff --git a/README.md b/README.md
index 490d4b86..15c5d266 100644
--- a/README.md
+++ b/README.md
@@ -76,7 +76,7 @@ subjects:
 Setup `kubectl` to authenticate with your identity provider.
 
 ```sh
-kubectl config set-credentials CLUSTER_NAME \
+kubectl config set-credentials NAME \
   --auth-provider oidc \
   --auth-provider-arg idp-issuer-url=https://accounts.google.com \
   --auth-provider-arg client-id=YOUR_CLIENT_ID.apps.googleusercontent.com \
@@ -170,7 +170,7 @@ subjects:
 Setup `kubectl` to authenticate with your identity provider.
 
 ```sh
-kubectl config set-credentials CLUSTER_NAME \
+kubectl config set-credentials NAME \
   --auth-provider oidc \
   --auth-provider-arg idp-issuer-url=https://keycloak.example.com/auth/realms/YOUR_REALM \
   --auth-provider-arg client-id=kubernetes \
diff --git a/cli/cli.go b/cli/cli.go
index 039d8528..9e136a9d 100644
--- a/cli/cli.go
+++ b/cli/cli.go
@@ -37,30 +37,33 @@ type CLI struct {
 func (c *CLI) ExpandKubeConfig() (string, error) {
 	d, err := homedir.Expand(c.KubeConfig)
 	if err != nil {
-		return "", fmt.Errorf("Could not expand %s", c.KubeConfig)
+		return "", fmt.Errorf("Could not expand %s: %s", c.KubeConfig, err)
 	}
 	return d, nil
 }
 
 // Run performs this command.
 func (c *CLI) Run(ctx context.Context) error {
+	log.Printf("Reading %s", c.KubeConfig)
 	path, err := c.ExpandKubeConfig()
 	if err != nil {
 		return err
 	}
-	log.Printf("Reading %s", path)
 	cfg, err := kubeconfig.Read(path)
 	if err != nil {
-		return fmt.Errorf("Could not load kubeconfig: %s", err)
+		return fmt.Errorf("Could not read kubeconfig: %s", err)
 	}
-	log.Printf("Using current context: %s", cfg.CurrentContext)
-	authInfo := kubeconfig.FindCurrentAuthInfo(cfg)
-	if authInfo == nil {
-		return fmt.Errorf("Could not find current context: %s", cfg.CurrentContext)
-	}
-	authProvider, err := kubeconfig.FindOIDCAuthProvider(authInfo)
+	log.Printf("Using current-context: %s", cfg.CurrentContext)
+	authProvider, err := kubeconfig.FindOIDCAuthProvider(cfg)
 	if err != nil {
-		return fmt.Errorf("Could not find auth-provider: %s", err)
+		return fmt.Errorf(`Could not find OIDC configuration in kubeconfig: %s
+			Did you setup kubectl for OIDC authentication?
+				kubectl config set-credentials %s \
+					--auth-provider oidc \
+					--auth-provider-arg idp-issuer-url=https://issuer.example.com \
+					--auth-provider-arg client-id=YOUR_CLIENT_ID \
+					--auth-provider-arg client-secret=YOUR_CLIENT_SECRET`,
+			err, cfg.CurrentContext)
 	}
 	tlsConfig, err := c.tlsConfig(authProvider)
 	if err != nil {
@@ -77,12 +80,12 @@ func (c *CLI) Run(ctx context.Context) error {
 	}
 	token, err := authConfig.GetTokenSet(ctx)
 	if err != nil {
-		return fmt.Errorf("Authentication error: %s", err)
+		return fmt.Errorf("Could not get token from OIDC provider: %s", err)
 	}
 
 	authProvider.SetIDToken(token.IDToken)
 	authProvider.SetRefreshToken(token.RefreshToken)
 	kubeconfig.Write(cfg, path)
-	log.Printf("Updated %s", path)
+	log.Printf("Updated %s", c.KubeConfig)
 	return nil
 }
diff --git a/cli/tls.go b/cli/tls.go
index ee7cc78e..522e69cc 100644
--- a/cli/tls.go
+++ b/cli/tls.go
@@ -13,25 +13,25 @@ import (
 
 func (c *CLI) tlsConfig(authProvider *kubeconfig.OIDCAuthProvider) (*tls.Config, error) {
 	p := x509.NewCertPool()
-	if authProvider.IDPCertificateAuthority() != "" {
-		b, err := ioutil.ReadFile(authProvider.IDPCertificateAuthority())
+	if ca := authProvider.IDPCertificateAuthority(); ca != "" {
+		b, err := ioutil.ReadFile(ca)
 		if err != nil {
-			return nil, fmt.Errorf("Could not read idp-certificate-authority: %s", err)
+			return nil, fmt.Errorf("Could not read %s: %s", ca, err)
 		}
 		if p.AppendCertsFromPEM(b) != true {
-			return nil, fmt.Errorf("Could not load CA certificate from idp-certificate-authority: %s", err)
+			return nil, fmt.Errorf("Could not append CA certificate from %s", ca)
 		}
-		log.Printf("Using CA certificate: %s", authProvider.IDPCertificateAuthority())
+		log.Printf("Using CA certificate: %s", ca)
 	}
-	if authProvider.IDPCertificateAuthorityData() != "" {
-		b, err := base64.StdEncoding.DecodeString(authProvider.IDPCertificateAuthorityData())
+	if ca := authProvider.IDPCertificateAuthorityData(); ca != "" {
+		b, err := base64.StdEncoding.DecodeString(ca)
 		if err != nil {
 			return nil, fmt.Errorf("Could not decode idp-certificate-authority-data: %s", err)
 		}
 		if p.AppendCertsFromPEM(b) != true {
-			return nil, fmt.Errorf("Could not load CA certificate from idp-certificate-authority-data: %s", err)
+			return nil, fmt.Errorf("Could not append CA certificate from idp-certificate-authority-data")
 		}
-		log.Printf("Using CA certificate of idp-certificate-authority-data")
+		log.Printf("Using CA certificate: idp-certificate-authority-data")
 	}
 
 	cfg := &tls.Config{InsecureSkipVerify: c.SkipTLSVerify}
diff --git a/kubeconfig/auth.go b/kubeconfig/auth.go
index f63d7b37..616aad95 100644
--- a/kubeconfig/auth.go
+++ b/kubeconfig/auth.go
@@ -7,23 +7,23 @@ import (
 	"k8s.io/client-go/tools/clientcmd/api"
 )
 
-// FindCurrentAuthInfo returns the authInfo of current context.
-// If the current context does not exist, this returns nil.
-func FindCurrentAuthInfo(config *api.Config) *api.AuthInfo {
+// FindOIDCAuthProvider returns the current OIDC authProvider.
+// If the context, auth-info or auth-provider does not exist, this returns an error.
+// If auth-provider is not "oidc", this returns an error.
+func FindOIDCAuthProvider(config *api.Config) (*OIDCAuthProvider, error) {
 	context := config.Contexts[config.CurrentContext]
 	if context == nil {
-		return nil
+		return nil, fmt.Errorf("context %s does not exist", config.CurrentContext)
+	}
+	authInfo := config.AuthInfos[context.AuthInfo]
+	if authInfo == nil {
+		return nil, fmt.Errorf("auth-info %s does not exist", context.AuthInfo)
 	}
-	return config.AuthInfos[context.AuthInfo]
-}
-
-// FindOIDCAuthProvider returns the OIDC authProvider.
-func FindOIDCAuthProvider(authInfo *api.AuthInfo) (*OIDCAuthProvider, error) {
 	if authInfo.AuthProvider == nil {
-		return nil, fmt.Errorf("auth-provider is not set, did you setup kubectl as listed here: https://github.com/int128/kubelogin")
+		return nil, fmt.Errorf("auth-provider is not set")
 	}
 	if authInfo.AuthProvider.Name != "oidc" {
-		return nil, fmt.Errorf("auth-provider `%s` is not supported", authInfo.AuthProvider.Name)
+		return nil, fmt.Errorf("auth-provider name is %s but must be oidc", authInfo.AuthProvider.Name)
 	}
 	return (*OIDCAuthProvider)(authInfo.AuthProvider), nil
 }
diff --git a/kubeconfig/kubeconfig.go b/kubeconfig/kubeconfig.go
index 3b83f2a1..ec8238b3 100644
--- a/kubeconfig/kubeconfig.go
+++ b/kubeconfig/kubeconfig.go
@@ -1,19 +1,13 @@
 package kubeconfig
 
 import (
-	"fmt"
-
 	"k8s.io/client-go/tools/clientcmd"
 	"k8s.io/client-go/tools/clientcmd/api"
 )
 
 // Read parses the file and returns the Config.
 func Read(path string) (*api.Config, error) {
-	config, err := clientcmd.LoadFromFile(path)
-	if err != nil {
-		return nil, fmt.Errorf("Could not load kubeconfig from %s: %s", path, err)
-	}
-	return config, nil
+	return clientcmd.LoadFromFile(path)
 }
 
 // Write writes the config to the file.
diff --git a/main.go b/main.go
index e89499d9..15c31859 100644
--- a/main.go
+++ b/main.go
@@ -15,6 +15,6 @@ func main() {
 	}
 	ctx := context.Background()
 	if err := c.Run(ctx); err != nil {
-		log.Fatal(err)
+		log.Fatalf("Error: %s", err)
 	}
 }