diff --git a/client/client.go b/client/client.go
new file mode 100644
index 0000000..51feb03
--- /dev/null
+++ b/client/client.go
@@ -0,0 +1,23 @@
+package client
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+)
+
+// Client is a Robinhood Agentic MCP client.
+type Client struct {
+	URL, Token, Name, Version string
+	HTTP                      *http.Client
+	Hook                      Caller
+	session                   any
+}
+
+// Call invokes an MCP tool by name and returns its JSON result.
+func (c *Client) Call(ctx context.Context, name string, args map[string]any) (json.RawMessage, error) {
+	if c.Hook != nil {
+		return c.Hook.Call(ctx, name, args)
+	}
+	return c.rpcCall(ctx, name, args)
+}
diff --git a/client/rpc.go b/client/rpc.go
new file mode 100644
index 0000000..2813880
--- /dev/null
+++ b/client/rpc.go
@@ -0,0 +1,68 @@
+package client
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+)
+
+type rpcReq struct {
+	JSONRPC string `json:"jsonrpc"`
+	ID      int    `json:"id"`
+	Method  string `json:"method"`
+	Params  any    `json:"params"`
+}
+
+type rpcResp struct {
+	Result json.RawMessage `json:"result"`
+	Error  *struct {
+		Message string `json:"message"`
+	} `json:"error"`
+}
+
+func (c *Client) rpcCall(ctx context.Context, name string, args map[string]any) (json.RawMessage, error) {
+	body, err := json.Marshal(rpcReq{
+		JSONRPC: "2.0",
+		ID:      1,
+		Method:  "tools/call",
+		Params:  map[string]any{"name": name, "arguments": args},
+	})
+	if err != nil {
+		return nil, ToolErrorf(name, "%w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.URL, bytes.NewReader(body))
+	if err != nil {
+		return nil, ToolErrorf(name, "%w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json, text/event-stream")
+	if c.Token != "" {
+		req.Header.Set("Authorization", "Bearer "+c.Token)
+	}
+	httpClient := c.HTTP
+	if httpClient == nil {
+		httpClient = http.DefaultClient
+	}
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return nil, ToolErrorf(name, "%w", err)
+	}
+	defer resp.Body.Close()
+	raw, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, ToolErrorf(name, "%w", err)
+	}
+	if resp.StatusCode >= 300 {
+		return nil, ToolErrorf(name, "http %d: %s", resp.StatusCode, raw)
+	}
+	var out rpcResp
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return nil, ToolErrorf(name, "%w", err)
+	}
+	if out.Error != nil {
+		return nil, ToolErrorf(name, "%s", out.Error.Message)
+	}
+	return out.Result, nil
+}
diff --git a/client/rpc_test.go b/client/rpc_test.go
new file mode 100644
index 0000000..4b94797
--- /dev/null
+++ b/client/rpc_test.go
@@ -0,0 +1,52 @@
+package client_test
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"testing"
+
+	"s1d3sw1ped/robinhood-agentic-mcp/client"
+	"s1d3sw1ped/robinhood-agentic-mcp/internal/rhntest"
+)
+
+func TestClientCall_rpcRoundTrip(t *testing.T) {
+	t.Parallel()
+	s := rhntest.New(t)
+	s.Token = "tok"
+	s.Set("get_equity_quotes", json.RawMessage(`{"quotes":[{"symbol":"MU"}]}`))
+	c := &client.Client{URL: s.URL, Token: "tok"}
+	raw, err := c.Call(context.Background(), "get_equity_quotes", map[string]any{"symbols": []string{"MU"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(raw) != `{"quotes":[{"symbol":"MU"}]}` {
+		t.Fatalf("%s", raw)
+	}
+	if s.LastName() != "get_equity_quotes" {
+		t.Fatal(s.LastName())
+	}
+}
+
+func TestClientCall_httpErrorIsToolError(t *testing.T) {
+	t.Parallel()
+	s := rhntest.New(t)
+	s.SetHTTPError(500, "nope")
+	c := &client.Client{URL: s.URL}
+	_, err := c.Call(context.Background(), "get_accounts", map[string]any{})
+	var te *client.ToolError
+	if !errors.As(err, &te) || te.Name != "get_accounts" {
+		t.Fatalf("%v", err)
+	}
+}
+
+func TestClientCall_hook(t *testing.T) {
+	t.Parallel()
+	c := &client.Client{Hook: client.Func(func(ctx context.Context, name string, args map[string]any) (json.RawMessage, error) {
+		return json.RawMessage(`{"ok":true}`), nil
+	})}
+	raw, err := c.Call(context.Background(), "x", nil)
+	if err != nil || string(raw) != `{"ok":true}` {
+		t.Fatalf("%s %v", raw, err)
+	}
+}