diff --git a/internal/adapter/openai/tool_sieve_core.go b/internal/adapter/openai/tool_sieve_core.go
index e651445..bc81882 100644
--- a/internal/adapter/openai/tool_sieve_core.go
+++ b/internal/adapter/openai/tool_sieve_core.go
@@ -114,8 +114,14 @@ func flushToolSieve(state *toolStreamSieveState, toolNames []string) []toolStrea
 		} else {
 			content := state.capture.String()
 			if content != "" {
-				state.noteText(content)
-				events = append(events, toolStreamEvent{Content: content})
+				// If the captured text looks like an incomplete XML tool call block,
+				// swallow it to prevent leaking raw XML tags to the client.
+				if hasOpenXMLToolTag(content) {
+					// Drop it silently — incomplete tool call.
+				} else {
+					state.noteText(content)
+					events = append(events, toolStreamEvent{Content: content})
+				}
 			}
 		}
 		state.capture.Reset()
@@ -200,6 +206,11 @@ func findToolSegmentStart(s string) int {
 	if start < 0 {
 		start = bestKeyIdx
 	}
+	// If the keyword matched inside an XML tag (e.g. "tool_calls" in "<tool_calls>"),
+	// back up past the '<' to capture the full tag.
+	if start > 0 && s[start-1] == '<' {
+		start--
+	}
 	if fenceStart, ok := openFenceStartBefore(s, start); ok {
 		return fenceStart
 	}
diff --git a/internal/adapter/openai/tool_sieve_xml.go b/internal/adapter/openai/tool_sieve_xml.go
index 885f50a..c4474af 100644
--- a/internal/adapter/openai/tool_sieve_xml.go
+++ b/internal/adapter/openai/tool_sieve_xml.go
@@ -12,6 +12,17 @@ import (
 var xmlToolCallClosingTags = []string{"</tool_calls>", "</tool_call>", "</invoke>", "</function_call>", "</function_calls>", "</tool_use>"}
 var xmlToolCallOpeningTags = []string{"<tool_calls", "<tool_call", "<invoke", "<function_call", "<function_calls", "<tool_use"}
 
+// xmlToolCallTagPairs maps each opening tag to its expected closing tag.
+// Order matters: longer/wrapper tags must be checked first.
+var xmlToolCallTagPairs = []struct{ open, close string }{
+	{"<tool_calls", "</tool_calls>"},
+	{"<tool_call", "</tool_call>"},
+	{"<function_calls", "</function_calls>"},
+	{"<function_call", "</function_call>"},
+	{"<invoke", "</invoke>"},
+	{"<tool_use", "</tool_use>"},
+}
+
 // xmlToolCallBlockPattern matches a complete XML tool call block (wrapper or standalone).
 var xmlToolCallBlockPattern = regexp.MustCompile(`(?is)(<tool_calls>\s*(?:.*?)\s*</tool_calls>|<tool_call>\s*(?:.*?)\s*</tool_call>|<invoke\b[^>]*>(?:.*?)</invoke>|<function_calls?\b[^>]*>(?:.*?)</function_calls?>|<tool_use>(?:.*?)</tool_use>)`)
 
@@ -22,59 +33,45 @@ var xmlToolTagsToDetect = []string{"<tool_calls>", "<tool_calls\n", "<tool_call>
 // consumeXMLToolCapture tries to extract complete XML tool call blocks from captured text.
 func consumeXMLToolCapture(captured string, toolNames []string) (prefix string, calls []util.ParsedToolCall, suffix string, ready bool) {
 	lower := strings.ToLower(captured)
-	// Find the earliest XML tool opening tag.
-	openIdx := -1
-	for _, tag := range xmlToolCallOpeningTags {
-		idx := strings.Index(lower, tag)
-		if idx >= 0 && (openIdx < 0 || idx < openIdx) {
-			openIdx = idx
+	// Find the FIRST matching open/close pair, preferring wrapper tags.
+	// Tag pairs are ordered longest-first (e.g. <tool_calls before <tool_call)
+	// so wrapper tags are checked before inner tags.
+	for _, pair := range xmlToolCallTagPairs {
+		openIdx := strings.Index(lower, pair.open)
+		if openIdx < 0 {
+			continue
 		}
-	}
-	if openIdx < 0 {
-		return "", nil, "", false
-	}
-
-	// Look for a matching closing tag.
-	closeIdx := -1
-	for _, tag := range xmlToolCallClosingTags {
-		idx := strings.Index(lower[openIdx:], tag)
-		if idx >= 0 {
-			absEnd := openIdx + idx + len(tag)
-			if closeIdx < 0 || absEnd > closeIdx {
-				closeIdx = absEnd
-			}
+		// Find the LAST occurrence of the specific closing tag to get the outermost block.
+		closeIdx := strings.LastIndex(lower, pair.close)
+		if closeIdx < openIdx {
+			// Opening tag is present but its specific closing tag hasn't arrived.
+			// Return not-ready so we keep buffering — do NOT fall through to
+			// try inner pairs (e.g. <tool_call inside <tool_calls).
+			return "", nil, "", false
 		}
-	}
-	if closeIdx <= 0 {
-		return "", nil, "", false
-	}
+		closeEnd := closeIdx + len(pair.close)
 
-	xmlBlock := captured[openIdx:closeIdx]
-	prefixPart := captured[:openIdx]
-	suffixPart := captured[closeIdx:]
-	parsed := util.ParseToolCalls(xmlBlock, toolNames)
-	if len(parsed) > 0 {
-		prefixPart, suffixPart = trimWrappingJSONFence(prefixPart, suffixPart)
-		return prefixPart, parsed, suffixPart, true
+		xmlBlock := captured[openIdx:closeEnd]
+		prefixPart := captured[:openIdx]
+		suffixPart := captured[closeEnd:]
+		parsed := util.ParseToolCalls(xmlBlock, toolNames)
+		if len(parsed) > 0 {
+			prefixPart, suffixPart = trimWrappingJSONFence(prefixPart, suffixPart)
+			return prefixPart, parsed, suffixPart, true
+		}
+		// Looks like XML tool syntax but failed to parse — consume it to avoid leak.
+		return prefixPart, nil, suffixPart, true
 	}
-	// Looks like XML tool syntax but failed to parse — consume it to avoid leak.
-	return prefixPart, nil, suffixPart, true
+	return "", nil, "", false
 }
 
 // hasOpenXMLToolTag returns true if captured text contains an XML tool opening tag
-// but no corresponding closing tag yet.
+// whose SPECIFIC closing tag has not appeared yet.
 func hasOpenXMLToolTag(captured string) bool {
 	lower := strings.ToLower(captured)
-	for _, tag := range xmlToolCallOpeningTags {
-		if strings.Contains(lower, tag) {
-			hasClosed := false
-			for _, ct := range xmlToolCallClosingTags {
-				if strings.Contains(lower, ct) {
-					hasClosed = true
-					break
-				}
-			}
-			if !hasClosed {
+	for _, pair := range xmlToolCallTagPairs {
+		if strings.Contains(lower, pair.open) {
+			if !strings.Contains(lower, pair.close) {
 				return true
 			}
 		}
diff --git a/internal/adapter/openai/tool_sieve_xml_test.go b/internal/adapter/openai/tool_sieve_xml_test.go
index b04f87b..b678345 100644
--- a/internal/adapter/openai/tool_sieve_xml_test.go
+++ b/internal/adapter/openai/tool_sieve_xml_test.go
@@ -153,3 +153,135 @@ func TestHasOpenXMLToolTag(t *testing.T) {
 		t.Fatal("should return false for plain text")
 	}
 }
+
+// Test the EXACT scenario the user reports: token-by-token streaming where
+// <tool_calls> tag arrives in small pieces.
+func TestProcessToolSieveTokenByTokenXMLNoLeak(t *testing.T) {
+	var state toolStreamSieveState
+	// Simulate DeepSeek model generating tokens one at a time.
+	chunks := []string{
+		"<",
+		"tool",
+		"_calls",
+		">\n",
+		"  <",
+		"tool",
+		"_call",
+		">\n",
+		"    <",
+		"tool",
+		"_name",
+		">",
+		"read",
+		"_file",
+		"</",
+		"tool",
+		"_name",
+		">\n",
+		"    <",
+		"parameters",
+		">",
+		`{"path"`,
+		`: "README.MD"`,
+		`}`,
+		"</",
+		"parameters",
+		">\n",
+		"  </",
+		"tool",
+		"_call",
+		">\n",
+		"</",
+		"tool",
+		"_calls",
+		">",
+	}
+	var events []toolStreamEvent
+	for _, c := range chunks {
+		events = append(events, processToolSieveChunk(&state, c, []string{"read_file"})...)
+	}
+	events = append(events, flushToolSieve(&state, []string{"read_file"})...)
+
+	var textContent string
+	var toolCalls int
+	for _, evt := range events {
+		if evt.Content != "" {
+			textContent += evt.Content
+		}
+		toolCalls += len(evt.ToolCalls)
+	}
+
+	if strings.Contains(textContent, "<tool_call") {
+		t.Fatalf("XML tool call content leaked to text in token-by-token mode: %q", textContent)
+	}
+	if strings.Contains(textContent, "tool_calls>") {
+		t.Fatalf("closing tag fragment leaked to text: %q", textContent)
+	}
+	if strings.Contains(textContent, "read_file") {
+		t.Fatalf("tool name leaked to text: %q", textContent)
+	}
+	if toolCalls == 0 {
+		t.Fatal("expected tool calls to be extracted, got none")
+	}
+}
+
+// Test that flushToolSieve on incomplete XML does NOT leak the raw XML content.
+func TestFlushToolSieveIncompleteXMLDoesNotLeak(t *testing.T) {
+	var state toolStreamSieveState
+	// XML block starts but stream ends before completion.
+	chunks := []string{
+		"<tool_calls>\n",
+		"  <tool_call>\n",
+		"    <tool_name>read_file</tool_name>\n",
+	}
+	var events []toolStreamEvent
+	for _, c := range chunks {
+		events = append(events, processToolSieveChunk(&state, c, []string{"read_file"})...)
+	}
+	// Stream ends abruptly - flush should NOT dump raw XML.
+	events = append(events, flushToolSieve(&state, []string{"read_file"})...)
+
+	var textContent string
+	for _, evt := range events {
+		if evt.Content != "" {
+			textContent += evt.Content
+		}
+	}
+
+	if strings.Contains(textContent, "<tool_call") {
+		t.Fatalf("incomplete XML leaked on flush: %q", textContent)
+	}
+}
+
+// Test that the opening tag "<tool_calls>\n  " is NOT emitted as text content.
+func TestOpeningXMLTagNotLeakedAsContent(t *testing.T) {
+	var state toolStreamSieveState
+	// First chunk is the opening tag - should be held, not emitted.
+	evts1 := processToolSieveChunk(&state, "<tool_calls>\n  ", []string{"read_file"})
+	for _, evt := range evts1 {
+		if strings.Contains(evt.Content, "<tool_calls>") {
+			t.Fatalf("opening tag leaked on first chunk: %q", evt.Content)
+		}
+	}
+
+	// Remaining content arrives.
+	evts2 := processToolSieveChunk(&state, "<tool_call>\n    <tool_name>read_file</tool_name>\n    <parameters>{\"path\":\"README.MD\"}</parameters>\n  </tool_call>\n</tool_calls>", []string{"read_file"})
+	evts2 = append(evts2, flushToolSieve(&state, []string{"read_file"})...)
+
+	var textContent string
+	var toolCalls int
+	allEvents := append(evts1, evts2...)
+	for _, evt := range allEvents {
+		if evt.Content != "" {
+			textContent += evt.Content
+		}
+		toolCalls += len(evt.ToolCalls)
+	}
+
+	if strings.Contains(textContent, "<tool_call") {
+		t.Fatalf("XML content leaked: %q", textContent)
+	}
+	if toolCalls == 0 {
+		t.Fatal("expected tool calls to be extracted")
+	}
+}
diff --git a/internal/js/helpers/stream-tool-sieve/sieve-xml.js b/internal/js/helpers/stream-tool-sieve/sieve-xml.js
index c96ff60..e286b92 100644
--- a/internal/js/helpers/stream-tool-sieve/sieve-xml.js
+++ b/internal/js/helpers/stream-tool-sieve/sieve-xml.js
@@ -1,63 +1,58 @@
 'use strict';
 const { parseToolCalls } = require('./parse');
-const {
-  XML_TOOL_OPENING_TAGS,
-  XML_TOOL_CLOSING_TAGS,
-} = require('./tool-keywords');
+
+// Tag pairs ordered longest-first: wrapper tags checked before inner tags.
+const XML_TOOL_TAG_PAIRS = [
+  { open: '<tool_calls', close: '</tool_calls>' },
+  { open: '<tool_call', close: '</tool_call>' },
+  { open: '<function_calls', close: '</function_calls>' },
+  { open: '<function_call', close: '</function_call>' },
+  { open: '<invoke', close: '</invoke>' },
+  { open: '<tool_use', close: '</tool_use>' },
+];
+
+const XML_TOOL_OPENING_TAGS = XML_TOOL_TAG_PAIRS.map(p => p.open);
 
 function consumeXMLToolCapture(captured, toolNames, trimWrappingJSONFence) {
   const lower = captured.toLowerCase();
-  let openIdx = -1;
-  for (const tag of XML_TOOL_OPENING_TAGS) {
-    const idx = lower.indexOf(tag);
-    if (idx >= 0 && (openIdx < 0 || idx < openIdx)) {
-      openIdx = idx;
+  // Find the FIRST matching open/close pair, preferring wrapper tags.
+  for (const pair of XML_TOOL_TAG_PAIRS) {
+    const openIdx = lower.indexOf(pair.open);
+    if (openIdx < 0) {
+      continue;
     }
-  }
-  if (openIdx < 0) {
-    return { ready: false, prefix: '', calls: [], suffix: '' };
-  }
-  let closeIdx = -1;
-  for (const tag of XML_TOOL_CLOSING_TAGS) {
-    const idx = lower.indexOf(tag, openIdx);
-    if (idx >= 0) {
-      const absEnd = idx + tag.length;
-      if (closeIdx < 0 || absEnd > closeIdx) {
-        closeIdx = absEnd;
-      }
+    // Find the LAST occurrence of the specific closing tag.
+    const closeIdx = lower.lastIndexOf(pair.close);
+    if (closeIdx < openIdx) {
+      // Opening tag present but specific closing tag hasn't arrived.
+      // Return not-ready — do NOT fall through to inner pairs.
+      return { ready: false, prefix: '', calls: [], suffix: '' };
     }
+    const closeEnd = closeIdx + pair.close.length;
+    const xmlBlock = captured.slice(openIdx, closeEnd);
+    let prefixPart = captured.slice(0, openIdx);
+    let suffixPart = captured.slice(closeEnd);
+    const parsed = parseToolCalls(xmlBlock, toolNames);
+    if (Array.isArray(parsed) && parsed.length > 0) {
+      const trimmedFence = trimWrappingJSONFence(prefixPart, suffixPart);
+      return {
+        ready: true,
+        prefix: trimmedFence.prefix,
+        calls: parsed,
+        suffix: trimmedFence.suffix,
+      };
+    }
+    // XML tool syntax but failed to parse — consume to avoid leak.
+    return { ready: true, prefix: prefixPart, calls: [], suffix: suffixPart };
   }
-  if (closeIdx <= 0) {
-    return { ready: false, prefix: '', calls: [], suffix: '' };
-  }
-  const xmlBlock = captured.slice(openIdx, closeIdx);
-  let prefixPart = captured.slice(0, openIdx);
-  let suffixPart = captured.slice(closeIdx);
-  const parsed = parseToolCalls(xmlBlock, toolNames);
-  if (Array.isArray(parsed) && parsed.length > 0) {
-    const trimmedFence = trimWrappingJSONFence(prefixPart, suffixPart);
-    return {
-      ready: true,
-      prefix: trimmedFence.prefix,
-      calls: parsed,
-      suffix: trimmedFence.suffix,
-    };
-  }
-  return { ready: true, prefix: prefixPart, calls: [], suffix: suffixPart };
+  return { ready: false, prefix: '', calls: [], suffix: '' };
 }
 
 function hasOpenXMLToolTag(captured) {
   const lower = captured.toLowerCase();
-  for (const tag of XML_TOOL_OPENING_TAGS) {
-    if (lower.includes(tag)) {
-      let hasClosed = false;
-      for (const ct of XML_TOOL_CLOSING_TAGS) {
-        if (lower.includes(ct)) {
-          hasClosed = true;
-          break;
-        }
-      }
-      if (!hasClosed) {
+  for (const pair of XML_TOOL_TAG_PAIRS) {
+    if (lower.includes(pair.open)) {
+      if (!lower.includes(pair.close)) {
         return true;
       }
     }
diff --git a/internal/js/helpers/stream-tool-sieve/sieve.js b/internal/js/helpers/stream-tool-sieve/sieve.js
index bd7e7cc..43c9224 100644
--- a/internal/js/helpers/stream-tool-sieve/sieve.js
+++ b/internal/js/helpers/stream-tool-sieve/sieve.js
@@ -191,7 +191,12 @@ function findToolSegmentStart(state, s) {
     }
     const keyIdx = bestKeyIdx;
     const start = s.slice(0, keyIdx).lastIndexOf('{');
-    const candidateStart = start >= 0 ? start : keyIdx;
+    let candidateStart = start >= 0 ? start : keyIdx;
+    // If the keyword matched inside an XML tag (e.g. "tool_calls" in "<tool_calls>"),
+    // back up past the '<' to capture the full tag.
+    if (candidateStart > 0 && s[candidateStart - 1] === '<') {
+      candidateStart--;
+    }
     if (!insideCodeFenceWithState(state, s.slice(0, candidateStart))) {
       return candidateStart;
     }