diff --git a/backend/internal/pkg/apicompat/anthropic_to_responses.go b/backend/internal/pkg/apicompat/anthropic_to_responses.go
index cc0c9e6c..f0af2936 100644
--- a/backend/internal/pkg/apicompat/anthropic_to_responses.go
+++ b/backend/internal/pkg/apicompat/anthropic_to_responses.go
@@ -325,16 +325,22 @@ func extractAnthropicTextFromBlocks(blocks []AnthropicContentBlock) string {
 }
 
 // convertAnthropicToolsToResponses maps Anthropic tool definitions to
-// Responses API function tools (input_schema → parameters).
+// Responses API tools. Server-side tools like web_search are mapped to their
+// OpenAI equivalents; regular tools become function tools.
 func convertAnthropicToolsToResponses(tools []AnthropicTool) []ResponsesTool {
-	out := make([]ResponsesTool, len(tools))
-	for i, t := range tools {
-		out[i] = ResponsesTool{
+	var out []ResponsesTool
+	for _, t := range tools {
+		// Anthropic server tools like "web_search_20250305" → OpenAI {"type":"web_search"}
+		if strings.HasPrefix(t.Type, "web_search") {
+			out = append(out, ResponsesTool{Type: "web_search"})
+			continue
+		}
+		out = append(out, ResponsesTool{
 			Type:        "function",
 			Name:        t.Name,
 			Description: t.Description,
 			Parameters:  t.InputSchema,
-		}
+		})
 	}
 	return out
 }
diff --git a/backend/internal/pkg/apicompat/responses_to_anthropic.go b/backend/internal/pkg/apicompat/responses_to_anthropic.go
index 39d36cf4..5409a0f4 100644
--- a/backend/internal/pkg/apicompat/responses_to_anthropic.go
+++ b/backend/internal/pkg/apicompat/responses_to_anthropic.go
@@ -54,6 +54,25 @@ func ResponsesToAnthropic(resp *ResponsesResponse, model string) *AnthropicRespo
 				Name:  item.Name,
 				Input: json.RawMessage(item.Arguments),
 			})
+		case "web_search_call":
+			toolUseID := "srvtoolu_" + item.ID
+			query := ""
+			if item.Action != nil {
+				query = item.Action.Query
+			}
+			inputJSON, _ := json.Marshal(map[string]string{"query": query})
+			blocks = append(blocks, AnthropicContentBlock{
+				Type:  "server_tool_use",
+				ID:    toolUseID,
+				Name:  "web_search",
+				Input: inputJSON,
+			})
+			emptyResults, _ := json.Marshal([]struct{}{})
+			blocks = append(blocks, AnthropicContentBlock{
+				Type:      "web_search_tool_result",
+				ToolUseID: toolUseID,
+				Content:   emptyResults,
+			})
 		}
 	}
 
@@ -369,12 +388,73 @@ func resToAnthHandleOutputItemDone(evt *ResponsesStreamEvent, state *ResponsesEv
 	if evt.Item == nil {
 		return nil
 	}
+
+	// Handle web_search_call → synthesize server_tool_use + web_search_tool_result blocks.
+	if evt.Item.Type == "web_search_call" && evt.Item.Status == "completed" {
+		return resToAnthHandleWebSearchDone(evt, state)
+	}
+
 	if state.ContentBlockOpen {
 		return closeCurrentBlock(state)
 	}
 	return nil
 }
 
+// resToAnthHandleWebSearchDone converts an OpenAI web_search_call output item
+// into Anthropic server_tool_use + web_search_tool_result content block pairs.
+// This allows Claude Code to count the searches performed.
+func resToAnthHandleWebSearchDone(evt *ResponsesStreamEvent, state *ResponsesEventToAnthropicState) []AnthropicStreamEvent {
+	var events []AnthropicStreamEvent
+	events = append(events, closeCurrentBlock(state)...)
+
+	toolUseID := "srvtoolu_" + evt.Item.ID
+	query := ""
+	if evt.Item.Action != nil {
+		query = evt.Item.Action.Query
+	}
+	inputJSON, _ := json.Marshal(map[string]string{"query": query})
+
+	// Emit server_tool_use block (start + stop).
+	idx1 := state.ContentBlockIndex
+	events = append(events, AnthropicStreamEvent{
+		Type:  "content_block_start",
+		Index: &idx1,
+		ContentBlock: &AnthropicContentBlock{
+			Type:  "server_tool_use",
+			ID:    toolUseID,
+			Name:  "web_search",
+			Input: inputJSON,
+		},
+	})
+	events = append(events, AnthropicStreamEvent{
+		Type:  "content_block_stop",
+		Index: &idx1,
+	})
+	state.ContentBlockIndex++
+
+	// Emit web_search_tool_result block (start + stop).
+	// Content is empty because OpenAI does not expose individual search results;
+	// the model consumes them internally and produces text output.
+	emptyResults, _ := json.Marshal([]struct{}{})
+	idx2 := state.ContentBlockIndex
+	events = append(events, AnthropicStreamEvent{
+		Type:  "content_block_start",
+		Index: &idx2,
+		ContentBlock: &AnthropicContentBlock{
+			Type:      "web_search_tool_result",
+			ToolUseID: toolUseID,
+			Content:   emptyResults,
+		},
+	})
+	events = append(events, AnthropicStreamEvent{
+		Type:  "content_block_stop",
+		Index: &idx2,
+	})
+	state.ContentBlockIndex++
+
+	return events
+}
+
 func resToAnthHandleCompleted(evt *ResponsesStreamEvent, state *ResponsesEventToAnthropicState) []AnthropicStreamEvent {
 	if state.MessageStopSent {
 		return nil
diff --git a/backend/internal/pkg/apicompat/types.go b/backend/internal/pkg/apicompat/types.go
index 435f5032..c482a339 100644
--- a/backend/internal/pkg/apicompat/types.go
+++ b/backend/internal/pkg/apicompat/types.go
@@ -60,6 +60,7 @@ type AnthropicContentBlock struct {
 
 // AnthropicTool describes a tool available to the model.
 type AnthropicTool struct {
+	Type        string          `json:"type,omitempty"`        // e.g. "web_search_20250305" for server tools
 	Name        string          `json:"name"`
 	Description string          `json:"description,omitempty"`
 	InputSchema json.RawMessage `json:"input_schema"` // JSON Schema object
@@ -217,7 +218,7 @@ type ResponsesIncompleteDetails struct {
 
 // ResponsesOutput is one output item in a Responses API response.
 type ResponsesOutput struct {
-	Type string `json:"type"` // "message" | "reasoning" | "function_call"
+	Type string `json:"type"` // "message" | "reasoning" | "function_call" | "web_search_call"
 
 	// type=message
 	ID      string                 `json:"id,omitempty"`
@@ -233,6 +234,15 @@ type ResponsesOutput struct {
 	CallID    string `json:"call_id,omitempty"`
 	Name      string `json:"name,omitempty"`
 	Arguments string `json:"arguments,omitempty"`
+
+	// type=web_search_call
+	Action *WebSearchAction `json:"action,omitempty"`
+}
+
+// WebSearchAction describes the search action in a web_search_call output item.
+type WebSearchAction struct {
+	Type  string `json:"type,omitempty"`  // "search"
+	Query string `json:"query,omitempty"` // primary search query
 }
 
 // ResponsesSummary is a summary text block inside a reasoning output.