diff --git a/pkg/agent/core.go b/pkg/agent/core.go
index a8be6b7..7a5728f 100644
--- a/pkg/agent/core.go
+++ b/pkg/agent/core.go
@@ -349,7 +349,14 @@ func (s *agentCore) Submit(ctx context.Context, input string, handler EventHandl
 	handle := &actionHandle{cancel: actCancel}
 	s.currentAction.Store(handle)
 
-	s.loopcfg.Output = handler
+	s.loopcfg.Output = func(ev Event) {
+		if ev.Role == "usage" && s.session != nil {
+			var in, out int
+			fmt.Sscanf(ev.Content, "%d %d", &in, &out)
+			s.session.addUsage(backend.Usage{InputTokens: in, OutputTokens: out})
+		}
+		handler(ev)
+	}
 	s.loopcfg.PopInject = func() string {
 		if p := s.pendingInject.Swap(nil); p != nil {
 			return *p
diff --git a/pkg/agent/loop.go b/pkg/agent/loop.go
index 92da0a1..371c52b 100644
--- a/pkg/agent/loop.go
+++ b/pkg/agent/loop.go
@@ -80,6 +80,12 @@ func run(ctx context.Context, cfg loopConfig, state state) error {
 			if ev.Done {
 				stopReason = ev.StopReason
 				done = true
+				if ev.Usage.InputTokens > 0 || ev.Usage.OutputTokens > 0 {
+					emit(cfg, Event{
+						Role:    "usage",
+						Content: fmt.Sprintf("%d %d", ev.Usage.InputTokens, ev.Usage.OutputTokens),
+					})
+				}
 				break
 			}
 		}
diff --git a/pkg/agent/session.go b/pkg/agent/session.go
index ac80bf3..6781cc0 100644
--- a/pkg/agent/session.go
+++ b/pkg/agent/session.go
@@ -69,6 +69,10 @@ type Session struct {
 	goal     string
 	messages []backend.Message
 	complete bool
+	// Cumulative usage tracking.
+	TotalInputTokens  int
+	TotalOutputTokens int
+	TotalRequests     int
 }
 
 // newSession creates a new Session with an initial user message.
@@ -86,6 +90,12 @@ func (s *Session) history() []backend.Message {
 
 func (s *Session) isComplete() bool { return s.complete }
 
+func (s *Session) addUsage(u backend.Usage) {
+	s.TotalInputTokens += u.InputTokens
+	s.TotalOutputTokens += u.OutputTokens
+	s.TotalRequests++
+}
+
 func (s *Session) update(assistant backend.Message, results []toolResult) error {
 	s.messages = append(s.messages, assistant)
 	for _, r := range results {
diff --git a/pkg/tools/builtin.go b/pkg/tools/builtin.go
index 1926b4e..844f8a8 100644
--- a/pkg/tools/builtin.go
+++ b/pkg/tools/builtin.go
@@ -90,3 +90,20 @@ func FileDefs() []ToolInfo {
 		},
 	}
 }
+
+// ReasoningDefs returns the ToolInfo definitions for the reasoning_* built-in tools.
+func ReasoningDefs() []ToolInfo {
+	return []ToolInfo{
+		{
+			Name:        "reasoning_think",
+			Description: "Internal reasoning tool for breaking down problems, planning approaches, analyzing constraints, and reasoning through multi-step solutions before acting. The thought content is not shown to the user.",
+			InputSchema: json.RawMessage(`{
+				"type": "object",
+				"required": ["thought"],
+				"properties": {
+					"thought": {"type": "string", "description": "A reflective note or intermediate reasoning step."}
+				}
+			}`),
+		},
+	}
+}
diff --git a/pkg/tools/reasoning/server.go b/pkg/tools/reasoning/server.go
new file mode 100644
index 0000000..69dd5a3
--- /dev/null
+++ b/pkg/tools/reasoning/server.go
@@ -0,0 +1,42 @@
+package reasoning
+
+import (
+	"context"
+	"encoding/json"
+
+	"ollie/pkg/tools"
+)
+
+// Decl returns a factory for a reasoning Server.
+func Decl() func() tools.Server { return func() tools.Server { return &Server{} } }
+
+// Server implements tools.Server for reasoning tools.
+type Server struct{}
+
+func (s *Server) ListTools() ([]tools.ToolInfo, error) {
+	return tools.ReasoningDefs(), nil
+}
+
+func (s *Server) CallTool(_ context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
+	switch tool {
+	case "reasoning_think":
+		var a struct {
+			Thought string `json:"thought"`
+		}
+		if json.Unmarshal(args, &a) != nil || a.Thought == "" {
+			return json.Marshal(map[string]any{
+				"content": []map[string]string{{"type": "text", "text": "error: missing required field 'thought'"}},
+			})
+		}
+		// No-op: the thought is recorded in conversation history by the loop.
+		return json.Marshal(map[string]any{
+			"content": []map[string]string{{"type": "text", "text": ""}},
+		})
+	default:
+		return json.Marshal(map[string]string{"error": "unknown tool: " + tool})
+	}
+}
+
+func (s *Server) Close() {}
+
+var _ tools.Server = (*Server)(nil)