diff --git a/packages/core/src/tools/smart-edit.test.ts b/packages/core/src/tools/smart-edit.test.ts
index a14dd8add1..9462ded913 100644
--- a/packages/core/src/tools/smart-edit.test.ts
+++ b/packages/core/src/tools/smart-edit.test.ts
@@ -240,6 +240,28 @@ describe('SmartEditTool', () => {
       expect(result.newContent).toBe(content);
       expect(result.occurrences).toBe(0);
     });
+
+    it('should perform a regex-based replacement for flexible intra-line whitespace', async () => {
+      // This case would fail with the previous exact and line-trimming flexible logic
+      // because the whitespace *within* the line is different.
+      const content = '  function  myFunc( a, b ) {\n    return a + b;\n  }';
+      const result = await calculateReplacement({
+        params: {
+          file_path: 'test.js',
+          instruction: 'test',
+          old_string: 'function myFunc(a, b) {', // Note the normalized whitespace
+          new_string: 'const yourFunc = (a, b) => {',
+        },
+        currentContent: content,
+        abortSignal,
+      });
+
+      // The indentation from the original line should be preserved and applied to the new string.
+      const expectedContent =
+        '  const yourFunc = (a, b) => {\n    return a + b;\n  }';
+      expect(result.newContent).toBe(expectedContent);
+      expect(result.occurrences).toBe(1);
+    });
   });
   describe('correctPath', () => {
     it('should correct a relative path if it is unambiguous', () => {
diff --git a/packages/core/src/tools/smart-edit.ts b/packages/core/src/tools/smart-edit.ts
index 6abd318c10..ea93e9023b 100644
--- a/packages/core/src/tools/smart-edit.ts
+++ b/packages/core/src/tools/smart-edit.ts
@@ -59,6 +59,15 @@ function restoreTrailingNewline(
   return modifiedContent;
 }
 
+/**
+ * Escapes characters with special meaning in regular expressions.
+ * @param str The string to escape.
+ * @returns The escaped string.
+ */
+function escapeRegex(str: string): string {
+  return str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // $& means the whole matched string
+}
+
 async function calculateExactReplacement(
   context: ReplacementContext,
 ): Promise<ReplacementResult | null> {
@@ -146,6 +155,68 @@ async function calculateFlexibleReplacement(
   return null;
 }
 
+async function calculateRegexReplacement(
+  context: ReplacementContext,
+): Promise<ReplacementResult | null> {
+  const { currentContent, params } = context;
+  const { old_string, new_string } = params;
+
+  // Normalize line endings for consistent processing.
+  const normalizedSearch = old_string.replace(/\r\n/g, '\n');
+  const normalizedReplace = new_string.replace(/\r\n/g, '\n');
+
+  // This logic is ported from your Python implementation.
+  // It builds a flexible, multi-line regex from a search string.
+  const delimiters = ['(', ')', ':', '[', ']', '{', '}', '>', '<', '='];
+
+  let processedString = normalizedSearch;
+  for (const delim of delimiters) {
+    processedString = processedString.split(delim).join(` ${delim} `);
+  }
+
+  // Split by any whitespace and remove empty strings.
+  const tokens = processedString.split(/\s+/).filter(Boolean);
+
+  if (tokens.length === 0) {
+    return null;
+  }
+
+  const escapedTokens = tokens.map(escapeRegex);
+  // Join tokens with `\s*` to allow for flexible whitespace between them.
+  const pattern = escapedTokens.join('\\s*');
+
+  // The final pattern captures leading whitespace (indentation) and then matches the token pattern.
+  // 'm' flag enables multi-line mode, so '^' matches the start of any line.
+  const finalPattern = `^(\\s*)${pattern}`;
+  const flexibleRegex = new RegExp(finalPattern, 'm');
+
+  const match = flexibleRegex.exec(currentContent);
+
+  if (!match) {
+    return null;
+  }
+
+  const indentation = match[1] || '';
+  const newLines = normalizedReplace.split('\n');
+  const newBlockWithIndent = newLines
+    .map((line) => `${indentation}${line}`)
+    .join('\n');
+
+  // Use replace with the regex to substitute the matched content.
+  // Since the regex doesn't have the 'g' flag, it will only replace the first occurrence.
+  const modifiedCode = currentContent.replace(
+    flexibleRegex,
+    newBlockWithIndent,
+  );
+
+  return {
+    newContent: restoreTrailingNewline(currentContent, modifiedCode),
+    occurrences: 1, // This method is designed to find and replace only the first occurrence.
+    finalOldString: normalizedSearch,
+    finalNewString: normalizedReplace,
+  };
+}
+
 /**
  * Detects the line ending style of a string.
  * @param content The string content to analyze.
@@ -184,6 +255,11 @@ export async function calculateReplacement(
     return flexibleResult;
   }
 
+  const regexResult = await calculateRegexReplacement(context);
+  if (regexResult) {
+    return regexResult;
+  }
+
   return {
     newContent: currentContent,
     occurrences: 0,