diff --git a/internal/mcp/handlers.go b/internal/mcp/handlers.go
index 186fe495..db865b4d 100644
--- a/internal/mcp/handlers.go
+++ b/internal/mcp/handlers.go
@@ -837,8 +837,10 @@ func (h *handlers) getMessage(ctx context.Context, req mcp.CallToolRequest) (*mc
 	}
 
 	maxChars := intArg(args, "max_chars", defaultBodyChars)
-	if maxChars <= 0 || maxChars > maxBodyChars {
+	if maxChars <= 0 {
 		maxChars = defaultBodyChars
+	} else if maxChars > maxBodyChars {
+		maxChars = maxBodyChars
 	}
 
 	fullBody := msg.BodyText
diff --git a/internal/mcp/server.go b/internal/mcp/server.go
index a30de679..e20252db 100644
--- a/internal/mcp/server.go
+++ b/internal/mcp/server.go
@@ -275,7 +275,7 @@ func getMessageTool() mcp.Tool {
 			mcp.Description("Byte offset from the start of body_text to center the window on (e.g. char_offset from search_in_message). Takes precedence over offset."),
 		),
 		mcp.WithNumber("max_chars",
-			mcp.Description("Maximum body_text bytes to return (default 2000, max 4000). Out-of-range values are silently replaced with the default."),
+			mcp.Description("Maximum body_text bytes to return (default 2000, max 4000). Values above 4000 are clamped to 4000; zero or negative values use the default."),
 		),
 	)
 }
diff --git a/internal/mcp/server_test.go b/internal/mcp/server_test.go
index 20cba26b..74075d65 100644
--- a/internal/mcp/server_test.go
+++ b/internal/mcp/server_test.go
@@ -844,6 +844,42 @@ func TestGetMessage(t *testing.T) {
 		assertpkg.Equal(t, 0, msg.Offset, "starts at body start")
 	})
 
+	t.Run("max_chars above cap clamps to 4000", func(t *testing.T) {
+		assert := assertpkg.New(t)
+		longBody := strings.Repeat("x", 5000)
+		eng2 := &querytest.MockEngine{
+			Messages: map[int64]*query.MessageDetail{
+				54: testutil.NewMessageDetail(54).WithBodyText(longBody).BuildPtr(),
+			},
+		}
+		h2 := newTestHandlers(eng2)
+		msg := runTool[getMessageResp](t, "get_message", h2.getMessage, map[string]any{
+			"id":        float64(54),
+			"max_chars": float64(5000),
+		})
+		assert.Equal(4000, msg.BodyReturned, "body_returned")
+		assert.Len(msg.BodyText, 4000, "clamped body_text")
+		assert.True(msg.HasMore, "has_more")
+	})
+
+	t.Run("max_chars zero uses default", func(t *testing.T) {
+		assert := assertpkg.New(t)
+		longBody := strings.Repeat("x", 5000)
+		eng2 := &querytest.MockEngine{
+			Messages: map[int64]*query.MessageDetail{
+				55: testutil.NewMessageDetail(55).WithBodyText(longBody).BuildPtr(),
+			},
+		}
+		h2 := newTestHandlers(eng2)
+		msg := runTool[getMessageResp](t, "get_message", h2.getMessage, map[string]any{
+			"id":        float64(55),
+			"max_chars": float64(0),
+		})
+		assert.Equal(2000, msg.BodyReturned, "body_returned")
+		assert.Len(msg.BodyText, 2000, "default body_text")
+		assert.True(msg.HasMore, "has_more")
+	})
+
 	errorCases := []struct {
 		name string
 		args map[string]any