diff --git a/mite/api.go b/mite/api.go
index 2f66b33..dadebfe 100644
--- a/mite/api.go
+++ b/mite/api.go
@@ -8,8 +8,9 @@ import (
 	"net/url"
 )
 
-const userAgent = "mite-go/0.1 (+github.com/leanovate/mite-go)"
 const layout = "2006-01-02"
+const contentType = "application/json"
+const userAgent = "mite-go/0.1 (+github.com/leanovate/mite-go)"
 
 type MiteApi interface {
 	TimeEntries(query *TimeEntryQuery) ([]*TimeEntry, error)
@@ -22,22 +23,23 @@ type MiteApi interface {
 }
 
 type miteApi struct {
-	url    string
+	base   string
 	key    string
 	client *http.Client
 }
 
-func NewMiteApi(url string, key string) MiteApi {
-	return &miteApi{url: url, key: key, client: &http.Client{}}
+func NewMiteApi(base string, key string) MiteApi {
+	return &miteApi{base: base, key: key, client: &http.Client{}}
 }
 
 func (a *miteApi) get(resource string, result interface{}) error {
-	req, err := http.NewRequest("GET", fmt.Sprintf("%s/%s", a.url, resource), nil)
+	req, err := http.NewRequest(http.MethodGet, a.url(resource), nil)
 	if err != nil {
 		return err
 	}
-	req.Header.Add("X-MiteApiKey", a.key)
+
 	req.Header.Add("User-Agent", userAgent)
+	req.Header.Add("X-MiteApiKey", a.key)
 
 	res, err := a.client.Do(req)
 	if err != nil {
@@ -45,6 +47,9 @@ func (a *miteApi) get(resource string, result interface{}) error {
 	}
 
 	defer func() { _ = res.Body.Close() }()
+	if err := a.check(res); err != nil {
+		return err
+	}
 
 	return json.NewDecoder(res.Body).Decode(result)
 }
@@ -63,13 +68,14 @@ func (a *miteApi) post(resource string, body interface{}, result interface{}) er
 		return err
 	}
 
-	req, err := http.NewRequest("POST", fmt.Sprintf("%s/%s", a.url, resource), bytes.NewBuffer(b))
+	req, err := http.NewRequest(http.MethodPost, a.url(resource), bytes.NewBuffer(b))
 	if err != nil {
 		return err
 	}
-	req.Header.Add("X-MiteApiKey", a.key)
+
+	req.Header.Add("Content-Type", contentType)
 	req.Header.Add("User-Agent", userAgent)
-	req.Header.Add("Content-Type", "application/json")
+	req.Header.Add("X-MiteApiKey", a.key)
 
 	res, err := a.client.Do(req)
 	if err != nil {
@@ -77,6 +83,9 @@ func (a *miteApi) post(resource string, body interface{}, result interface{}) er
 	}
 
 	defer func() { _ = res.Body.Close() }()
+	if err := a.check(res); err != nil {
+		return err
+	}
 
 	return json.NewDecoder(res.Body).Decode(result)
 }
@@ -87,32 +96,66 @@ func (a *miteApi) patch(resource string, body interface{}) error {
 		return err
 	}
 
-	req, err := http.NewRequest("PATCH", fmt.Sprintf("%s/%s", a.url, resource), bytes.NewBuffer(b))
+	req, err := http.NewRequest(http.MethodPatch, a.url(resource), bytes.NewBuffer(b))
 	if err != nil {
 		return err
 	}
-	req.Header.Add("X-MiteApiKey", a.key)
+
+	req.Header.Add("Content-Type", contentType)
 	req.Header.Add("User-Agent", userAgent)
-	req.Header.Add("Content-Type", "application/json")
+	req.Header.Add("X-MiteApiKey", a.key)
 
 	res, err := a.client.Do(req)
+	if err != nil {
+		return err
+	}
 
 	defer func() { _ = res.Body.Close() }()
+	if err := a.check(res); err != nil {
+		return err
+	}
 
-	return err
+	return nil
 }
 
 func (a *miteApi) delete(resource string) error {
-	req, err := http.NewRequest("DELETE", fmt.Sprintf("%s/%s", a.url, resource), nil)
+	req, err := http.NewRequest(http.MethodDelete, a.url(resource), nil)
 	if err != nil {
 		return err
 	}
-	req.Header.Add("X-MiteApiKey", a.key)
+
 	req.Header.Add("User-Agent", userAgent)
+	req.Header.Add("X-MiteApiKey", a.key)
 
 	res, err := a.client.Do(req)
+	if err != nil {
+		return err
+	}
 
 	defer func() { _ = res.Body.Close() }()
+	if err := a.check(res); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (a *miteApi) url(resource string) string {
+	return fmt.Sprintf("%s/%s", a.base, resource)
+}
+
+func (a *miteApi) check(res *http.Response) error {
+	if res.StatusCode < 400 {
+		return nil
+	}
+
+	msg := struct {
+		Error string `json:"error"`
+	}{}
+	err := json.NewDecoder(res.Body).Decode(&msg)
+	if err != nil {
+		return fmt.Errorf("failed to %s %s", res.Request.Method, res.Request.RequestURI)
+	}
 
-	return err
+	return fmt.Errorf("failed to %s %s: %s", res.Request.Method, res.Request.RequestURI, msg.Error)
 }