diff --git a/internal/application/service/agent_parallel_tool_calls_config_test.go b/internal/application/service/agent_parallel_tool_calls_config_test.go
new file mode 100644
index 0000000000..4c43478c30
--- /dev/null
+++ b/internal/application/service/agent_parallel_tool_calls_config_test.go
@@ -0,0 +1,67 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/Tencent/WeKnora/internal/config"
+	"github.com/Tencent/WeKnora/internal/types"
+	"github.com/stretchr/testify/require"
+)
+
+// The engine already knows how to run a round's tool calls concurrently
+// (AgentEngine.executeToolCallsParallel, gated on AgentConfig.ParallelToolCalls),
+// but nothing ever set that flag: buildAgentConfig copies CustomAgentConfig into
+// the runtime AgentConfig field by field and this one was absent, so the gate
+// read the zero value and the parallel branch was unreachable for every custom
+// agent. Failure was silent — tools just kept running one at a time.
+func TestAgentConfigCarriesTheParallelToolCallsPreference(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		want bool
+	}{
+		{name: "opted in", want: true},
+		{name: "opted out", want: false},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			svc := &sessionService{
+				cfg:                   &config.Config{},
+				webSearchProviderRepo: &sharedAgentWebSearchRepo{},
+			}
+			req := &types.QARequest{
+				Session: &types.Session{ID: "session-1", TenantID: 1},
+				CustomAgent: &types.CustomAgent{
+					TenantID: 1,
+					Config: types.CustomAgentConfig{
+						MaxIterations:     5,
+						ParallelToolCalls: tc.want,
+					},
+				},
+			}
+
+			agentConfig, err := svc.buildAgentConfig(t.Context(), req, &types.Tenant{ID: 1}, 1)
+			require.NoError(t, err)
+			require.Equal(t, tc.want, agentConfig.ParallelToolCalls)
+		})
+	}
+}
+
+// Agents saved before this option existed must keep running their tools
+// sequentially: tools are not required to be side-effect free, so silently
+// turning on concurrency for them would be a behavior change, not a fix.
+func TestAgentConfigDefaultsParallelToolCallsOff(t *testing.T) {
+	svc := &sessionService{
+		cfg:                   &config.Config{},
+		webSearchProviderRepo: &sharedAgentWebSearchRepo{},
+	}
+	req := &types.QARequest{
+		Session: &types.Session{ID: "session-1", TenantID: 1},
+		CustomAgent: &types.CustomAgent{
+			TenantID: 1,
+			Config:   types.CustomAgentConfig{MaxIterations: 5},
+		},
+	}
+
+	agentConfig, err := svc.buildAgentConfig(t.Context(), req, &types.Tenant{ID: 1}, 1)
+	require.NoError(t, err)
+	require.False(t, agentConfig.ParallelToolCalls)
+}
diff --git a/internal/application/service/session_agent_qa.go b/internal/application/service/session_agent_qa.go
index c194cd26d7..8cb2d4a6bb 100644
--- a/internal/application/service/session_agent_qa.go
+++ b/internal/application/service/session_agent_qa.go
@@ -256,6 +256,7 @@ func (s *sessionService) buildAgentConfig(
 	customAgent := req.CustomAgent
 	agentConfig := &types.AgentConfig{
 		MaxIterations:               customAgent.Config.MaxIterations,
+		ParallelToolCalls:           customAgent.Config.ParallelToolCalls,
 		Temperature:                 customAgent.Config.Temperature,
 		WebSearchEnabled:            customAgent.Config.WebSearchEnabled && req.WebSearchEnabled,
 		WebSearchMaxResults:         customAgent.Config.WebSearchMaxResults,
diff --git a/internal/types/custom_agent.go b/internal/types/custom_agent.go
index 6160c50dc5..01b93e61a1 100644
--- a/internal/types/custom_agent.go
+++ b/internal/types/custom_agent.go
@@ -132,6 +132,10 @@ type CustomAgentConfig struct {
 	// ===== Agent Mode Settings =====
 	// Maximum iterations for ReAct loop (only for agent type)
 	MaxIterations int `yaml:"max_iterations" json:"max_iterations"`
+	// Whether independent tool calls in one round run concurrently (default: false).
+	// Opt-in because tools are not required to be side-effect free; agents that
+	// depend on tools observing each other's writes must leave this off.
+	ParallelToolCalls bool `yaml:"parallel_tool_calls" json:"parallel_tool_calls,omitempty"`
 	// Timeout for a single LLM call in seconds (0 = use global default)
 	LLMCallTimeout int `yaml:"llm_call_timeout" json:"llm_call_timeout,omitempty"`
 	// Allowed tools (only for agent type)