diff --git a/pkg/api/client.go b/pkg/api/client.go
new file mode 100644
index 00000000..8699ed70
--- /dev/null
+++ b/pkg/api/client.go
@@ -0,0 +1,127 @@
+package api
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"github.com/gitploy-io/gitploy/pkg/e"
+)
+
+type (
+	Client struct {
+		// Reuse a single struct instead of allocating one for each service on the heap.
+		common *client
+
+		// Services used for talking to different parts of the Gitploy API.
+	}
+
+	client struct {
+		// HTTP client used to communicate with the API.
+		httpClient *http.Client
+
+		// Base URL for API requests. BaseURL should
+		// always be specified with a trailing slash.
+		BaseURL *url.URL
+	}
+
+	// service struct {
+	// 	client *client
+	// }
+
+	ErrorResponse struct {
+		Code    string `json:"code"`
+		Message string `json:"message"`
+	}
+)
+
+func NewClient(host string, httpClient *http.Client) *Client {
+	if httpClient == nil {
+		httpClient = &http.Client{}
+	}
+
+	baseURL, _ := url.Parse(host)
+
+	c := &Client{
+		common: &client{httpClient: httpClient, BaseURL: baseURL},
+	}
+
+	return c
+}
+
+// NewRequest creates an API request. A relative URL can be provided in urlStr,
+// in which case it is resolved relative to the BaseURL of the Client.
+// Relative URLs should always be specified without a preceding slash. If
+// specified, the value pointed to by body is JSON encoded and included as the
+// request body.
+func (c *client) NewRequest(method, urlStr string, body interface{}) (*http.Request, error) {
+	if !strings.HasSuffix(c.BaseURL.Path, "/") {
+		return nil, fmt.Errorf("BaseURL must have a trailing slash, but %q does not", c.BaseURL)
+	}
+	u, err := c.BaseURL.Parse(urlStr)
+	if err != nil {
+		return nil, err
+	}
+
+	var buf io.ReadWriter
+	if body != nil {
+		buf = &bytes.Buffer{}
+		enc := json.NewEncoder(buf)
+		enc.SetEscapeHTML(false)
+		err := enc.Encode(body)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	req, err := http.NewRequest(method, u.String(), buf)
+	if err != nil {
+		return nil, err
+	}
+
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+
+	return req, nil
+}
+
+// Do sends an API request and returns the API response. The API response is
+// JSON decoded and stored in the value pointed to by v, or returned as an
+// error if an API error has occurred.
+func (c *client) Do(ctx context.Context, req *http.Request, v interface{}) error {
+	if ctx == nil {
+		return fmt.Errorf("There is no context")
+	}
+
+	res, err := c.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("Failed to request: %w", err)
+	}
+
+	defer res.Body.Close()
+
+	// Return internal errors
+	if res.StatusCode > 299 {
+		errRes := &ErrorResponse{}
+
+		out, _ := ioutil.ReadAll(res.Body)
+		if err := json.Unmarshal(out, errRes); err != nil {
+			return fmt.Errorf("Failed to parse an error response: %w", err)
+		}
+
+		return e.NewErrorWithMessage(e.ErrorCode(errRes.Code), errRes.Message, nil)
+	}
+
+	if v != nil {
+		return json.NewDecoder(res.Body).Decode(v)
+	}
+
+	return nil
+}
diff --git a/pkg/api/client_test.go b/pkg/api/client_test.go
new file mode 100644
index 00000000..1ef63e54
--- /dev/null
+++ b/pkg/api/client_test.go
@@ -0,0 +1,57 @@
+package api
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/gitploy-io/gitploy/pkg/e"
+)
+
+func TestClient_Do(t *testing.T) {
+	t.Run("Return an internal error", func(t *testing.T) {
+		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusNotFound)
+			fmt.Fprint(w, `{"code": "entity_not_found", "message": "It is not found."}`)
+		}))
+		defer ts.Close()
+
+		// Append '/' to avoid an trailing slash error.
+		baseURL, _ := url.Parse(ts.URL + "/")
+		c := &client{httpClient: http.DefaultClient, BaseURL: baseURL}
+
+		req, err := c.NewRequest("GET", baseURL.Path, nil)
+		if err != nil {
+			t.Fatalf("Failed to build a request: %s", err)
+		}
+
+		err = c.Do(context.Background(), req, nil)
+		if !e.HasErrorCode(err, e.ErrorCodeEntityNotFound) {
+			t.Fatalf("Do = %v, want ErrorCodeEntityNotFound", err)
+		}
+	})
+
+	t.Run("Return OK response", func(t *testing.T) {
+		ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		}))
+		defer ts.Close()
+
+		// Append '/' to avoid an trailing slash error.
+		baseURL, _ := url.Parse(ts.URL + "/")
+		c := &client{httpClient: http.DefaultClient, BaseURL: baseURL}
+
+		req, err := c.NewRequest("GET", baseURL.Path, nil)
+		if err != nil {
+			t.Fatalf("Failed to build a request: %s", err)
+		}
+
+		err = c.Do(context.Background(), req, nil)
+		if err != nil {
+			t.Fatalf("Do returns an error: %s", err)
+		}
+	})
+}