diff --git a/internal/translator/claude/openai/chat-completions/claude_openai_request.go b/internal/translator/claude/openai/chat-completions/claude_openai_request.go
index fa6c0451e..a528bbb80 100644
--- a/internal/translator/claude/openai/chat-completions/claude_openai_request.go
+++ b/internal/translator/claude/openai/chat-completions/claude_openai_request.go
@@ -368,6 +368,17 @@ func convertOpenAIRequestToClaude(modelName string, inputRawJSON []byte, stream,
 				if !gjson.GetBytes(anthropicTool, "cache_control").Exists() {
 					anthropicTool = common.AttachCacheControl(anthropicTool, function)
 				}
+				strict := function.Get("strict")
+				if !strict.Exists() {
+					strict = tool.Get("strict")
+				}
+				if strict.Exists() {
+					if strict.Type == gjson.True {
+						anthropicTool, _ = sjson.SetBytes(anthropicTool, "strict", true)
+					} else if strict.Type == gjson.False {
+						anthropicTool, _ = sjson.SetBytes(anthropicTool, "strict", false)
+					}
+				}
 
 				anthropicTools = append(anthropicTools, anthropicTool)
 			}
diff --git a/internal/translator/claude/openai/chat-completions/claude_openai_request_test.go b/internal/translator/claude/openai/chat-completions/claude_openai_request_test.go
index 012cb2043..b211aed1d 100644
--- a/internal/translator/claude/openai/chat-completions/claude_openai_request_test.go
+++ b/internal/translator/claude/openai/chat-completions/claude_openai_request_test.go
@@ -1188,3 +1188,101 @@ func TestConvertOpenAIRequestToClaude_ToolChoice(t *testing.T) {
 		}
 	})
 }
+
+func TestConvertOpenAIRequestToClaude_ToolStrict(t *testing.T) {
+	t.Run("preserves strict true on function tool", func(t *testing.T) {
+		inputJSON := `{
+			"model": "claude-sonnet-4-6",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"type": "function",
+					"function": {
+						"name": "tool_a",
+						"description": "Controlled tool.",
+						"strict": true,
+						"parameters": {"type": "object", "properties": {}}
+					}
+				}
+			]
+		}`
+		result := ConvertOpenAIRequestToClaude("claude-sonnet-4-6", []byte(inputJSON), false)
+		toolStrict := gjson.GetBytes(result, "tools.0.strict")
+		if !toolStrict.Exists() {
+			t.Fatalf("expected tools.0.strict to exist in Claude output: %s", result)
+		}
+		if !toolStrict.Bool() {
+			t.Fatalf("expected tools.0.strict to be true, got %v", toolStrict.Value())
+		}
+	})
+
+	t.Run("preserves strict true when on top level tool", func(t *testing.T) {
+		inputJSON := `{
+			"model": "claude-sonnet-4-6",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"type": "function",
+					"strict": true,
+					"function": {
+						"name": "tool_b",
+						"description": "Controlled tool.",
+						"parameters": {"type": "object", "properties": {}}
+					}
+				}
+			]
+		}`
+		result := ConvertOpenAIRequestToClaude("claude-sonnet-4-6", []byte(inputJSON), false)
+		toolStrict := gjson.GetBytes(result, "tools.0.strict")
+		if !toolStrict.Exists() || !toolStrict.Bool() {
+			t.Fatalf("expected tools.0.strict to be true, got %s", result)
+		}
+	})
+
+	t.Run("preserves strict false on function tool", func(t *testing.T) {
+		inputJSON := `{
+			"model": "claude-sonnet-4-6",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"type": "function",
+					"function": {
+						"name": "tool_c",
+						"description": "Controlled tool.",
+						"strict": false,
+						"parameters": {"type": "object", "properties": {}}
+					}
+				}
+			]
+		}`
+		result := ConvertOpenAIRequestToClaude("claude-sonnet-4-6", []byte(inputJSON), false)
+		toolStrict := gjson.GetBytes(result, "tools.0.strict")
+		if !toolStrict.Exists() {
+			t.Fatalf("expected tools.0.strict to exist in Claude output: %s", result)
+		}
+		if toolStrict.Bool() {
+			t.Fatalf("expected tools.0.strict to be false, got %v", toolStrict.Value())
+		}
+	})
+
+	t.Run("omits strict when not provided", func(t *testing.T) {
+		inputJSON := `{
+			"model": "claude-sonnet-4-6",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"type": "function",
+					"function": {
+						"name": "tool_d",
+						"description": "Controlled tool.",
+						"parameters": {"type": "object", "properties": {}}
+					}
+				}
+			]
+		}`
+		result := ConvertOpenAIRequestToClaude("claude-sonnet-4-6", []byte(inputJSON), false)
+		if gjson.GetBytes(result, "tools.0.strict").Exists() {
+			t.Fatalf("expected tools.0.strict to be omitted when not provided, got %s", result)
+		}
+	})
+}
diff --git a/internal/translator/gemini/claude/gemini_claude_request.go b/internal/translator/gemini/claude/gemini_claude_request.go
index b05058e1b..821938f0a 100644
--- a/internal/translator/gemini/claude/gemini_claude_request.go
+++ b/internal/translator/gemini/claude/gemini_claude_request.go
@@ -239,9 +239,13 @@ func convertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool,
 	}
 
 	// tools
+	var toolItems [][]byte
+	hasStrictTool := false
 	if toolsResult := gjson.GetBytes(rawJSON, "tools"); toolsResult.IsArray() {
-		var toolItems [][]byte
 		toolsResult.ForEach(func(_, toolResult gjson.Result) bool {
+			if toolResult.Get("strict").Type == gjson.True {
+				hasStrictTool = true
+			}
 			inputSchemaResult := toolResult.Get("input_schema")
 			if inputSchemaResult.Exists() && inputSchemaResult.IsObject() {
 				inputSchema := util.CleanJSONSchemaForGemini(inputSchemaResult.Raw)
@@ -281,7 +285,7 @@ func convertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool,
 
 	// tool_choice
 	toolChoiceResult := gjson.GetBytes(rawJSON, "tool_choice")
-	if toolChoiceResult.Exists() {
+	if toolChoiceResult.Exists() && toolChoiceResult.Type != gjson.Null {
 		toolChoiceType := ""
 		toolChoiceName := ""
 		if toolChoiceResult.IsObject() {
@@ -293,7 +297,11 @@ func convertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool,
 
 		switch toolChoiceType {
 		case "auto":
-			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "AUTO")
+			if hasStrictTool {
+				out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "VALIDATED")
+			} else {
+				out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "AUTO")
+			}
 		case "none":
 			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "NONE")
 		case "any":
@@ -304,6 +312,8 @@ func convertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool,
 				out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.allowedFunctionNames", []string{util.SanitizeFunctionName(toolChoiceName)})
 			}
 		}
+	} else if hasStrictTool && len(toolItems) > 0 {
+		out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "VALIDATED")
 	}
 
 	// Map Anthropic thinking -> Gemini thinking config when enabled
diff --git a/internal/translator/gemini/claude/gemini_claude_request_test.go b/internal/translator/gemini/claude/gemini_claude_request_test.go
index 54a052efd..4dea1e13f 100644
--- a/internal/translator/gemini/claude/gemini_claude_request_test.go
+++ b/internal/translator/gemini/claude/gemini_claude_request_test.go
@@ -1,6 +1,7 @@
 package claude
 
 import (
+	"fmt"
 	"testing"
 
 	internalsignature "github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
@@ -492,3 +493,132 @@ func TestConvertClaudeRequestToGemini_ToolResultWithTrailingSystemReminderReorde
 		t.Fatalf("unexpected functionResponse.id in parts[1]: %q", gotID)
 	}
 }
+
+func TestConvertClaudeRequestToGemini_ToolStrictMapsToValidatedMode(t *testing.T) {
+	tests := []struct {
+		name         string
+		toolChoice   string
+		expectedMode string
+		allowedNames []string
+	}{
+		{
+			name:         "absent tool_choice maps to VALIDATED",
+			toolChoice:   "",
+			expectedMode: "VALIDATED",
+		},
+		{
+			name:         "explicit auto tool_choice maps to VALIDATED",
+			toolChoice:   `"tool_choice": {"type": "auto"},`,
+			expectedMode: "VALIDATED",
+		},
+		{
+			name:         "null tool_choice maps to VALIDATED",
+			toolChoice:   `"tool_choice": null,`,
+			expectedMode: "VALIDATED",
+		},
+		{
+			name:         "none tool_choice maps to NONE",
+			toolChoice:   `"tool_choice": {"type": "none"},`,
+			expectedMode: "NONE",
+		},
+		{
+			name:         "any tool_choice maps to ANY",
+			toolChoice:   `"tool_choice": {"type": "any"},`,
+			expectedMode: "ANY",
+		},
+		{
+			name:         "specific tool maps to ANY with allowedFunctionNames",
+			toolChoice:   `"tool_choice": {"type": "tool", "name": "tool_a"},`,
+			expectedMode: "ANY",
+			allowedNames: []string{"tool_a"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			inputJSON := fmt.Sprintf(`{
+				"model": "gemini-3.8-flash",
+				"messages": [{"role": "user", "content": "hi"}],
+				%s
+				"tools": [
+					{
+						"name": "tool_a",
+						"description": "Controlled tool.",
+						"strict": true,
+						"input_schema": {"type": "object", "properties": {}}
+					}
+				]
+			}`, tt.toolChoice)
+
+			result := ConvertClaudeRequestToGemini("gemini-3.8-flash", []byte(inputJSON), false)
+			if gjson.GetBytes(result, "tools.0.functionDeclarations.0.strict").Exists() {
+				t.Fatalf("strict must be removed from functionDeclarations: %s", result)
+			}
+			mode := gjson.GetBytes(result, "toolConfig.functionCallingConfig.mode").String()
+			if mode != tt.expectedMode {
+				t.Fatalf("expected toolConfig.functionCallingConfig.mode = %q, got %q. Output: %s", tt.expectedMode, mode, result)
+			}
+			if len(tt.allowedNames) > 0 {
+				allowed := gjson.GetBytes(result, "toolConfig.functionCallingConfig.allowedFunctionNames").Array()
+				if len(allowed) != len(tt.allowedNames) {
+					t.Fatalf("expected %d allowedFunctionNames, got %d", len(tt.allowedNames), len(allowed))
+				}
+				for i, name := range tt.allowedNames {
+					if allowed[i].String() != name {
+						t.Fatalf("allowedFunctionNames[%d] = %q, want %q", i, allowed[i].String(), name)
+					}
+				}
+			}
+		})
+	}
+
+	t.Run("mixed tools where one is strict maps to VALIDATED", func(t *testing.T) {
+		inputJSON := []byte(`{
+			"model": "gemini-3.8-flash",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"name": "tool_a",
+					"description": "Loose tool.",
+					"strict": false,
+					"input_schema": {"type": "object", "properties": {}}
+				},
+				{
+					"name": "tool_b",
+					"description": "Strict tool.",
+					"strict": true,
+					"input_schema": {"type": "object", "properties": {}}
+				}
+			]
+		}`)
+		result := ConvertClaudeRequestToGemini("gemini-3.8-flash", inputJSON, false)
+		mode := gjson.GetBytes(result, "toolConfig.functionCallingConfig.mode").String()
+		if mode != "VALIDATED" {
+			t.Fatalf("expected mode = 'VALIDATED' for mixed tools, got %q", mode)
+		}
+	})
+
+	t.Run("non-strict tools omit toolConfig mode", func(t *testing.T) {
+		inputJSON := []byte(`{
+			"model": "gemini-3.8-flash",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"name": "tool_a",
+					"description": "Loose tool.",
+					"strict": false,
+					"input_schema": {"type": "object", "properties": {}}
+				},
+				{
+					"name": "tool_b",
+					"description": "Unspecified tool.",
+					"input_schema": {"type": "object", "properties": {}}
+				}
+			]
+		}`)
+		result := ConvertClaudeRequestToGemini("gemini-3.8-flash", inputJSON, false)
+		if gjson.GetBytes(result, "toolConfig").Exists() {
+			t.Fatalf("expected toolConfig not to be set when no strict tools and no tool_choice, got: %s", result)
+		}
+	})
+}
diff --git a/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go b/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
index f69b94ae3..b9ea2deac 100644
--- a/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
+++ b/internal/translator/gemini/openai/chat-completions/gemini_openai_request.go
@@ -327,6 +327,7 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 	declaredOriginalToSanitized := make(map[string]string)
 	sanitizedToOriginalCounts := make(map[string]int)
 	var functionDeclarations [][]byte
+	hasStrictTool := false
 	tools := gjson.GetBytes(rawJSON, "tools")
 	toolResults := tools.Array()
 	if tools.IsArray() && len(toolResults) > 0 {
@@ -394,8 +395,20 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 							fnRawBytes, _ = sjson.SetRawBytes(fnRawBytes, "parametersJsonSchema", []byte(cleanedParameters))
 						}
 					}
-					if gjson.GetBytes(fnRawBytes, "strict").Exists() {
-						fnRawBytes, _ = sjson.DeleteBytes(fnRawBytes, "strict")
+					strictVal := gjson.GetBytes(fnRawBytes, "strict")
+					if !strictVal.Exists() {
+						strictVal = fn.Get("strict")
+						if !strictVal.Exists() {
+							strictVal = t.Get("strict")
+						}
+					}
+					if strictVal.Exists() {
+						if strictVal.Type == gjson.True {
+							hasStrictTool = true
+						}
+						if gjson.GetBytes(fnRawBytes, "strict").Exists() {
+							fnRawBytes, _ = sjson.DeleteBytes(fnRawBytes, "strict")
+						}
 					}
 					functionDeclarations = append(functionDeclarations, fnRawBytes)
 				}
@@ -468,6 +481,8 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 				allowedList = append(allowedList, gjson.GetBytes(fnRaw, "name").String())
 			}
 			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.allowedFunctionNames", allowedList)
+		} else if hasStrictTool {
+			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "VALIDATED")
 		} else {
 			// Mode AUTO: functionDeclarations contains only allowed tools, mode is AUTO without allowedFunctionNames.
 			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "AUTO")
@@ -482,7 +497,11 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 
 		switch toolChoiceType {
 		case "auto":
-			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "AUTO")
+			if hasStrictTool {
+				out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "VALIDATED")
+			} else {
+				out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "AUTO")
+			}
 		case "none":
 			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "NONE")
 		case "required", "any":
@@ -504,6 +523,8 @@ func ConvertOpenAIRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 			// Unrecognized tool_choice type: fail-closed.
 			out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "NONE")
 		}
+	} else if hasStrictTool && len(functionDeclarations) > 0 {
+		out, _ = sjson.SetBytes(out, "toolConfig.functionCallingConfig.mode", "VALIDATED")
 	}
 
 	// parallel_tool_calls handling:
diff --git a/internal/translator/gemini/openai/chat-completions/gemini_openai_request_test.go b/internal/translator/gemini/openai/chat-completions/gemini_openai_request_test.go
index e0a21c85c..c865a1c44 100644
--- a/internal/translator/gemini/openai/chat-completions/gemini_openai_request_test.go
+++ b/internal/translator/gemini/openai/chat-completions/gemini_openai_request_test.go
@@ -1,6 +1,7 @@
 package chat_completions
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/router-for-me/CLIProxyAPI/v7/internal/signature"
@@ -999,3 +1000,157 @@ func TestConvertOpenAIRequestToGemini_ToolChoice(t *testing.T) {
 		}
 	})
 }
+
+func TestConvertOpenAIRequestToGemini_ToolStrictMapsToValidatedMode(t *testing.T) {
+	tests := []struct {
+		name         string
+		toolChoice   string // empty means absent
+		expectedMode string
+		allowedNames []string
+	}{
+		{
+			name:         "absent tool_choice maps to VALIDATED",
+			toolChoice:   "",
+			expectedMode: "VALIDATED",
+		},
+		{
+			name:         "explicit auto tool_choice maps to VALIDATED",
+			toolChoice:   `"tool_choice": "auto",`,
+			expectedMode: "VALIDATED",
+		},
+		{
+			name:         "null tool_choice maps to VALIDATED",
+			toolChoice:   `"tool_choice": null,`,
+			expectedMode: "VALIDATED",
+		},
+		{
+			name:         "required tool_choice maps to ANY",
+			toolChoice:   `"tool_choice": "required",`,
+			expectedMode: "ANY",
+		},
+		{
+			name:         "none tool_choice maps to NONE",
+			toolChoice:   `"tool_choice": "none",`,
+			expectedMode: "NONE",
+		},
+		{
+			name:         "specific function tool_choice maps to ANY with allowedFunctionNames",
+			toolChoice:   `"tool_choice": {"type": "function", "function": {"name": "tool_a"}},`,
+			expectedMode: "ANY",
+			allowedNames: []string{"tool_a"},
+		},
+		{
+			name:         "allowed_tools with auto mode and strict tool maps to VALIDATED",
+			toolChoice:   `"tool_choice": {"type": "allowed_tools", "allowed_tools": {"mode": "auto", "tools": [{"type": "function", "function": {"name": "tool_a"}}]}},`,
+			expectedMode: "VALIDATED",
+		},
+		{
+			name:         "allowed_tools with required mode and strict tool maps to ANY",
+			toolChoice:   `"tool_choice": {"type": "allowed_tools", "allowed_tools": {"mode": "required", "tools": [{"type": "function", "function": {"name": "tool_a"}}]}},`,
+			expectedMode: "ANY",
+			allowedNames: []string{"tool_a"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			inputJSON := fmt.Sprintf(`{
+				"model": "gemini-3.1-pro-high",
+				"messages": [{"role": "user", "content": "hi"}],
+				%s
+				"tools": [
+					{
+						"type": "function",
+						"function": {
+							"name": "tool_a",
+							"description": "Controlled tool.",
+							"strict": true,
+							"parameters": {"type": "object", "properties": {}}
+						}
+					}
+				]
+			}`, tt.toolChoice)
+			result := ConvertOpenAIRequestToGemini("gemini-3.1-pro-high", []byte(inputJSON), false)
+			if gjson.GetBytes(result, "tools.0.functionDeclarations.0.strict").Exists() {
+				t.Fatalf("tools.0.functionDeclarations.0.strict should be removed from function declaration: %s", result)
+			}
+			mode := gjson.GetBytes(result, "toolConfig.functionCallingConfig.mode").String()
+			if mode != tt.expectedMode {
+				t.Fatalf("expected toolConfig.functionCallingConfig.mode = %q, got %q. Output: %s", tt.expectedMode, mode, result)
+			}
+			if len(tt.allowedNames) > 0 {
+				allowed := gjson.GetBytes(result, "toolConfig.functionCallingConfig.allowedFunctionNames").Array()
+				if len(allowed) != len(tt.allowedNames) {
+					t.Fatalf("expected %d allowedFunctionNames, got %d", len(tt.allowedNames), len(allowed))
+				}
+				for i, name := range tt.allowedNames {
+					if allowed[i].String() != name {
+						t.Fatalf("allowedFunctionNames[%d] = %q, want %q", i, allowed[i].String(), name)
+					}
+				}
+			}
+		})
+	}
+
+	t.Run("mixed tools where one is strict maps to VALIDATED", func(t *testing.T) {
+		inputJSON := `{
+			"model": "gemini-3.1-pro-high",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"type": "function",
+					"function": {
+						"name": "tool_a",
+						"description": "Loose tool.",
+						"strict": false,
+						"parameters": {"type": "object", "properties": {}}
+					}
+				},
+				{
+					"type": "function",
+					"function": {
+						"name": "tool_b",
+						"description": "Strict tool.",
+						"strict": true,
+						"parameters": {"type": "object", "properties": {}}
+					}
+				}
+			]
+		}`
+		result := ConvertOpenAIRequestToGemini("gemini-3.1-pro-high", []byte(inputJSON), false)
+		mode := gjson.GetBytes(result, "toolConfig.functionCallingConfig.mode").String()
+		if mode != "VALIDATED" {
+			t.Fatalf("expected mode = 'VALIDATED' for mixed tools, got %q", mode)
+		}
+	})
+
+	t.Run("non-strict tools omit toolConfig mode", func(t *testing.T) {
+		inputJSON := `{
+			"model": "gemini-3.1-pro-high",
+			"messages": [{"role": "user", "content": "hi"}],
+			"tools": [
+				{
+					"type": "function",
+					"function": {
+						"name": "tool_a",
+						"description": "Loose tool.",
+						"strict": false,
+						"parameters": {"type": "object", "properties": {}}
+					}
+				},
+				{
+					"type": "function",
+					"function": {
+						"name": "tool_b",
+						"description": "Unspecified tool.",
+						"parameters": {"type": "object", "properties": {}}
+					}
+				}
+			]
+		}`
+		result := ConvertOpenAIRequestToGemini("gemini-3.1-pro-high", []byte(inputJSON), false)
+		if gjson.GetBytes(result, "toolConfig").Exists() {
+			t.Fatalf("expected toolConfig not to be set when no strict tools and no tool_choice, got: %s", result)
+		}
+	})
+}