diff --git a/internal/js/helpers/stream-tool-sieve/sieve.js b/internal/js/helpers/stream-tool-sieve/sieve.js
index c567545..b930b25 100644
--- a/internal/js/helpers/stream-tool-sieve/sieve.js
+++ b/internal/js/helpers/stream-tool-sieve/sieve.js
@@ -6,6 +6,7 @@ const {
 } = require('./state');
 const { parseStandaloneToolCallsDetailed } = require('./parse');
 const { extractJSONObjectFrom } = require('./jsonscan');
+const { TOOL_SEGMENT_KEYWORDS, earliestKeywordIndex } = require('./tool-keywords');
 function processToolSieveChunk(state, chunk, toolNames) {
   if (!state) {
     return [];
@@ -151,20 +152,9 @@ function findToolSegmentStart(state, s) {
     return -1;
   }
   const lower = s.toLowerCase();
-  const keywords = ['tool_calls', 'function.name:', '[tool_call_history]', '[tool_result_history]'];
   let offset = 0;
   while (true) {
-    let bestKeyIdx = -1;
-    let matchedKeyword = '';
-    for (const kw of keywords) {
-      const idx = lower.indexOf(kw, offset);
-      if (idx >= 0) {
-        if (bestKeyIdx < 0 || idx < bestKeyIdx) {
-          bestKeyIdx = idx;
-          matchedKeyword = kw;
-        }
-      }
-    }
+    const { index: bestKeyIdx, keyword: matchedKeyword } = earliestKeywordIndex(lower, TOOL_SEGMENT_KEYWORDS, offset);
     if (bestKeyIdx < 0) {
       return -1;
     }
@@ -184,14 +174,7 @@ function consumeToolCapture(state, toolNames) {
     return { ready: false, prefix: '', calls: [], suffix: '' };
   }
   const lower = captured.toLowerCase();
-  let keyIdx = -1;
-  const keywords = ['tool_calls', 'function.name:', '[tool_call_history]', '[tool_result_history]'];
-  for (const kw of keywords) {
-    const idx = lower.indexOf(kw);
-    if (idx >= 0 && (keyIdx < 0 || idx < keyIdx)) {
-      keyIdx = idx;
-    }
-  }
+  const { index: keyIdx } = earliestKeywordIndex(lower, TOOL_SEGMENT_KEYWORDS);
   if (keyIdx < 0) {
     return { ready: false, prefix: '', calls: [], suffix: '' };
   }
diff --git a/internal/js/helpers/stream-tool-sieve/tool-keywords.js b/internal/js/helpers/stream-tool-sieve/tool-keywords.js
new file mode 100644
index 0000000..34cd226
--- /dev/null
+++ b/internal/js/helpers/stream-tool-sieve/tool-keywords.js
@@ -0,0 +1,29 @@
+'use strict';
+
+const TOOL_SEGMENT_KEYWORDS = [
+  'tool_calls',
+  'function.name:',
+  '[tool_call_history]',
+  '[tool_result_history]',
+];
+
+function earliestKeywordIndex(text, keywords = TOOL_SEGMENT_KEYWORDS, offset = 0) {
+  if (!text) {
+    return { index: -1, keyword: '' };
+  }
+  let index = -1;
+  let keyword = '';
+  for (const kw of keywords) {
+    const candidate = text.indexOf(kw, offset);
+    if (candidate >= 0 && (index < 0 || candidate < index)) {
+      index = candidate;
+      keyword = kw;
+    }
+  }
+  return { index, keyword };
+}
+
+module.exports = {
+  TOOL_SEGMENT_KEYWORDS,
+  earliestKeywordIndex,
+};