diff --git a/luminos_lib/ai.py b/luminos_lib/ai.py
index d57d860..6b8b3d5 100644
--- a/luminos_lib/ai.py
+++ b/luminos_lib/ai.py
@@ -19,12 +19,7 @@ from datetime import datetime, timezone
 
 import anthropic
 import magic
-import tree_sitter
-import tree_sitter_python
-import tree_sitter_javascript
-import tree_sitter_rust
-import tree_sitter_go
-
+from luminos_lib.ast_parser import parse_structure
 from luminos_lib.cache import _CacheManager, _get_investigation_id
 from luminos_lib.capabilities import check_ai_dependencies
 
@@ -48,33 +43,6 @@ _SKIP_DIRS = {
 # Commands the run_command tool is allowed to execute.
 _COMMAND_WHITELIST = {"wc", "file", "grep", "head", "tail", "stat", "du", "find"}
 
-# tree-sitter language registry: extension → (grammar_module, language_name)
-_TS_LANGUAGES = {
-    ".py": (tree_sitter_python, "python"),
-    ".js": (tree_sitter_javascript, "javascript"),
-    ".jsx": (tree_sitter_javascript, "javascript"),
-    ".mjs": (tree_sitter_javascript, "javascript"),
-    ".rs": (tree_sitter_rust, "rust"),
-    ".go": (tree_sitter_go, "go"),
-}
-
-# Precompute Language objects once.
-_TS_LANG_CACHE = {}
-
-
-def _get_ts_parser(ext):
-    """Return a (Parser, language_name) tuple for a file extension, or None."""
-    entry = _TS_LANGUAGES.get(ext)
-    if entry is None:
-        return None
-    module, lang_name = entry
-    if lang_name not in _TS_LANG_CACHE:
-        _TS_LANG_CACHE[lang_name] = tree_sitter.Language(module.language())
-    lang = _TS_LANG_CACHE[lang_name]
-    parser = tree_sitter.Parser(lang)
-    return parser, lang_name
-
-
 # ---------------------------------------------------------------------------
 # Helpers
 # ---------------------------------------------------------------------------
@@ -533,181 +501,7 @@ def _tool_parse_structure(args, target, _cache):
         path = os.path.join(target, path)
     if not _path_is_safe(path, target):
         return f"Error: path '{path}' is outside the target directory."
-    if not os.path.isfile(path):
-        return f"Error: '{path}' is not a file."
-
-    ext = os.path.splitext(path)[1].lower()
-    ts = _get_ts_parser(ext)
-    if ts is None:
-        return f"Error: no grammar for extension '{ext}'. Supported: {', '.join(sorted(_TS_LANGUAGES.keys()))}"
-
-    parser, lang_name = ts
-
-    try:
-        with open(path, "rb") as f:
-            source = f.read()
-    except OSError as e:
-        return f"Error reading file: {e}"
-
-    tree = parser.parse(source)
-    root = tree.root_node
-    source_text = source.decode("utf-8", errors="replace")
-    lines = source_text.split("\n")
-    line_count = len(lines)
-
-    functions = []
-    classes = []
-    imports = []
-    has_docstrings = False
-    comment_lines = 0
-
-    def _walk(node):
-        nonlocal has_docstrings, comment_lines
-        for child in node.children:
-            ntype = child.type
-
-            # Comments
-            if ntype in ("comment", "line_comment", "block_comment"):
-                comment_lines += child.text.decode("utf-8", errors="replace").count("\n") + 1
-
-            # Python
-            if lang_name == "python":
-                if ntype == "function_definition":
-                    functions.append(_py_func_sig(child))
-                elif ntype == "class_definition":
-                    classes.append(_py_class(child))
-                elif ntype in ("import_statement", "import_from_statement"):
-                    imports.append(child.text.decode("utf-8", errors="replace").strip())
-                elif ntype == "expression_statement":
-                    first = child.children[0] if child.children else None
-                    if first and first.type == "string":
-                        has_docstrings = True
-
-            # JavaScript
-            elif lang_name == "javascript":
-                if ntype in ("function_declaration", "arrow_function",
-                             "function"):
-                    functions.append(_js_func_sig(child))
-                elif ntype == "class_declaration":
-                    classes.append(_js_class(child))
-                elif ntype in ("import_statement",):
-                    imports.append(child.text.decode("utf-8", errors="replace").strip())
-
-            # Rust
-            elif lang_name == "rust":
-                if ntype == "function_item":
-                    functions.append(_rust_func_sig(child))
-                elif ntype in ("struct_item", "enum_item", "impl_item"):
-                    classes.append(_rust_struct(child))
-                elif ntype == "use_declaration":
-                    imports.append(child.text.decode("utf-8", errors="replace").strip())
-
-            # Go
-            elif lang_name == "go":
-                if ntype == "function_declaration":
-                    functions.append(_go_func_sig(child))
-                elif ntype == "type_declaration":
-                    classes.append(_go_type(child))
-                elif ntype == "import_declaration":
-                    imports.append(child.text.decode("utf-8", errors="replace").strip())
-
-            _walk(child)
-
-    _walk(root)
-
-    code_lines = max(1, line_count - comment_lines)
-    result = {
-        "language": lang_name,
-        "functions": functions[:50],
-        "classes": classes[:30],
-        "imports": imports[:30],
-        "line_count": line_count,
-        "has_docstrings": has_docstrings,
-        "has_comments": comment_lines > 0,
-        "comment_to_code_ratio": round(comment_lines / code_lines, 2),
-    }
-    return json.dumps(result, indent=2)
-
-
-# --- tree-sitter extraction helpers ---
-
-def _child_by_type(node, *types):
-    for c in node.children:
-        if c.type in types:
-            return c
-    return None
-
-
-def _text(node):
-    return node.text.decode("utf-8", errors="replace") if node else ""
-
-
-def _py_func_sig(node):
-    name = _text(_child_by_type(node, "identifier"))
-    params = _text(_child_by_type(node, "parameters"))
-    ret = _child_by_type(node, "type")
-    sig = f"{name}{params}"
-    if ret:
-        sig += f" -> {_text(ret)}"
-    return sig
-
-
-def _py_class(node):
-    name = _text(_child_by_type(node, "identifier"))
-    methods = []
-    body = _child_by_type(node, "block")
-    if body:
-        for child in body.children:
-            if child.type == "function_definition":
-                methods.append(_py_func_sig(child))
-    return {"name": name, "methods": methods[:20]}
-
-
-def _js_func_sig(node):
-    name = _text(_child_by_type(node, "identifier"))
-    params = _text(_child_by_type(node, "formal_parameters"))
-    return f"{name}{params}" if name else f"(anonymous){params}"
-
-
-def _js_class(node):
-    name = _text(_child_by_type(node, "identifier"))
-    methods = []
-    body = _child_by_type(node, "class_body")
-    if body:
-        for child in body.children:
-            if child.type == "method_definition":
-                mname = _text(_child_by_type(child, "property_identifier"))
-                mparams = _text(_child_by_type(child, "formal_parameters"))
-                methods.append(f"{mname}{mparams}")
-    return {"name": name, "methods": methods[:20]}
-
-
-def _rust_func_sig(node):
-    name = _text(_child_by_type(node, "identifier"))
-    params = _text(_child_by_type(node, "parameters"))
-    ret = _child_by_type(node, "type_identifier", "generic_type",
-                         "reference_type", "scoped_type_identifier")
-    sig = f"{name}{params}"
-    if ret:
-        sig += f" -> {_text(ret)}"
-    return sig
-
-
-def _rust_struct(node):
-    name = _text(_child_by_type(node, "type_identifier"))
-    return {"name": name or _text(node)[:60], "methods": []}
-
-
-def _go_func_sig(node):
-    name = _text(_child_by_type(node, "identifier"))
-    params = _text(_child_by_type(node, "parameter_list"))
-    return f"{name}{params}"
-
-
-def _go_type(node):
-    spec = _child_by_type(node, "type_spec")
-    name = _text(_child_by_type(spec, "type_identifier")) if spec else ""
-    return {"name": name or _text(node)[:60], "methods": []}
+    return parse_structure(path)
 
 
 def _tool_write_cache(args, _target, cache):
diff --git a/luminos_lib/ast_parser.py b/luminos_lib/ast_parser.py
new file mode 100644
index 0000000..607be19
--- /dev/null
+++ b/luminos_lib/ast_parser.py
@@ -0,0 +1,314 @@
+"""AST structure extraction for Luminos using tree-sitter."""
+
+import json
+import os
+
+import tree_sitter
+import tree_sitter_python
+import tree_sitter_javascript
+import tree_sitter_rust
+import tree_sitter_go
+
+# Extension → (grammar_module, language_name)
+_TS_LANGUAGES = {
+    ".py": (tree_sitter_python, "python"),
+    ".js": (tree_sitter_javascript, "javascript"),
+    ".jsx": (tree_sitter_javascript, "javascript"),
+    ".mjs": (tree_sitter_javascript, "javascript"),
+    ".rs": (tree_sitter_rust, "rust"),
+    ".go": (tree_sitter_go, "go"),
+}
+
+# Precomputed Language objects.
+_TS_LANG_CACHE = {}
+
+
+def _get_ts_parser(ext):
+    """Return a (Parser, language_name) tuple for a file extension, or None."""
+    entry = _TS_LANGUAGES.get(ext)
+    if entry is None:
+        return None
+    module, lang_name = entry
+    if lang_name not in _TS_LANG_CACHE:
+        _TS_LANG_CACHE[lang_name] = tree_sitter.Language(module.language())
+    lang = _TS_LANG_CACHE[lang_name]
+    parser = tree_sitter.Parser(lang)
+    return parser, lang_name
+
+
+# ---------------------------------------------------------------------------
+# Tree-sitter node helpers
+# ---------------------------------------------------------------------------
+
+def _child_by_type(node, *types):
+    for c in node.children:
+        if c.type in types:
+            return c
+    return None
+
+
+def _text(node):
+    return node.text.decode("utf-8", errors="replace") if node else ""
+
+
+# ---------------------------------------------------------------------------
+# Per-language handlers: (root_node, source_bytes) -> dict
+# ---------------------------------------------------------------------------
+
+def _parse_python(root, source):
+    functions = []
+    classes = []
+    imports = []
+    has_docstrings = False
+    comment_lines = 0
+
+    def _walk(node):
+        nonlocal has_docstrings, comment_lines
+        for child in node.children:
+            ntype = child.type
+
+            if ntype in ("comment", "line_comment", "block_comment"):
+                comment_lines += child.text.decode("utf-8", errors="replace").count("\n") + 1
+
+            if ntype == "function_definition":
+                name = _text(_child_by_type(child, "identifier"))
+                params = _text(_child_by_type(child, "parameters"))
+                ret = _child_by_type(child, "type")
+                sig = f"{name}{params}"
+                if ret:
+                    sig += f" -> {_text(ret)}"
+                functions.append(sig)
+            elif ntype == "class_definition":
+                name = _text(_child_by_type(child, "identifier"))
+                methods = []
+                body = _child_by_type(child, "block")
+                if body:
+                    for c in body.children:
+                        if c.type == "function_definition":
+                            mname = _text(_child_by_type(c, "identifier"))
+                            mparams = _text(_child_by_type(c, "parameters"))
+                            mret = _child_by_type(c, "type")
+                            msig = f"{mname}{mparams}"
+                            if mret:
+                                msig += f" -> {_text(mret)}"
+                            methods.append(msig)
+                classes.append({"name": name, "methods": methods[:20]})
+            elif ntype in ("import_statement", "import_from_statement"):
+                imports.append(child.text.decode("utf-8", errors="replace").strip())
+            elif ntype == "expression_statement":
+                first = child.children[0] if child.children else None
+                if first and first.type == "string":
+                    has_docstrings = True
+
+            _walk(child)
+
+    _walk(root)
+
+    source_text = source.decode("utf-8", errors="replace")
+    line_count = len(source_text.split("\n"))
+    code_lines = max(1, line_count - comment_lines)
+
+    return {
+        "language": "python",
+        "functions": functions[:50],
+        "classes": classes[:30],
+        "imports": imports[:30],
+        "line_count": line_count,
+        "has_docstrings": has_docstrings,
+        "has_comments": comment_lines > 0,
+        "comment_to_code_ratio": round(comment_lines / code_lines, 2),
+    }
+
+
+def _parse_javascript(root, source):
+    functions = []
+    classes = []
+    imports = []
+    comment_lines = 0
+
+    def _walk(node):
+        nonlocal comment_lines
+        for child in node.children:
+            ntype = child.type
+
+            if ntype in ("comment", "line_comment", "block_comment"):
+                comment_lines += child.text.decode("utf-8", errors="replace").count("\n") + 1
+
+            if ntype in ("function_declaration", "arrow_function", "function"):
+                name = _text(_child_by_type(child, "identifier"))
+                params = _text(_child_by_type(child, "formal_parameters"))
+                functions.append(f"{name}{params}" if name else f"(anonymous){params}")
+            elif ntype == "class_declaration":
+                name = _text(_child_by_type(child, "identifier"))
+                methods = []
+                body = _child_by_type(child, "class_body")
+                if body:
+                    for c in body.children:
+                        if c.type == "method_definition":
+                            mname = _text(_child_by_type(c, "property_identifier"))
+                            mparams = _text(_child_by_type(c, "formal_parameters"))
+                            methods.append(f"{mname}{mparams}")
+                classes.append({"name": name, "methods": methods[:20]})
+            elif ntype == "import_statement":
+                imports.append(child.text.decode("utf-8", errors="replace").strip())
+
+            _walk(child)
+
+    _walk(root)
+
+    source_text = source.decode("utf-8", errors="replace")
+    line_count = len(source_text.split("\n"))
+    code_lines = max(1, line_count - comment_lines)
+
+    return {
+        "language": "javascript",
+        "functions": functions[:50],
+        "classes": classes[:30],
+        "imports": imports[:30],
+        "line_count": line_count,
+        "has_docstrings": False,
+        "has_comments": comment_lines > 0,
+        "comment_to_code_ratio": round(comment_lines / code_lines, 2),
+    }
+
+
+def _parse_rust(root, source):
+    functions = []
+    classes = []
+    imports = []
+    comment_lines = 0
+
+    def _walk(node):
+        nonlocal comment_lines
+        for child in node.children:
+            ntype = child.type
+
+            if ntype in ("comment", "line_comment", "block_comment"):
+                comment_lines += child.text.decode("utf-8", errors="replace").count("\n") + 1
+
+            if ntype == "function_item":
+                name = _text(_child_by_type(child, "identifier"))
+                params = _text(_child_by_type(child, "parameters"))
+                ret = _child_by_type(child, "type_identifier", "generic_type",
+                                     "reference_type", "scoped_type_identifier")
+                sig = f"{name}{params}"
+                if ret:
+                    sig += f" -> {_text(ret)}"
+                functions.append(sig)
+            elif ntype in ("struct_item", "enum_item", "impl_item"):
+                name = _text(_child_by_type(child, "type_identifier"))
+                classes.append({"name": name or _text(child)[:60], "methods": []})
+            elif ntype == "use_declaration":
+                imports.append(child.text.decode("utf-8", errors="replace").strip())
+
+            _walk(child)
+
+    _walk(root)
+
+    source_text = source.decode("utf-8", errors="replace")
+    line_count = len(source_text.split("\n"))
+    code_lines = max(1, line_count - comment_lines)
+
+    return {
+        "language": "rust",
+        "functions": functions[:50],
+        "classes": classes[:30],
+        "imports": imports[:30],
+        "line_count": line_count,
+        "has_docstrings": False,
+        "has_comments": comment_lines > 0,
+        "comment_to_code_ratio": round(comment_lines / code_lines, 2),
+    }
+
+
+def _parse_go(root, source):
+    functions = []
+    classes = []
+    imports = []
+    comment_lines = 0
+
+    def _walk(node):
+        nonlocal comment_lines
+        for child in node.children:
+            ntype = child.type
+
+            if ntype in ("comment", "line_comment", "block_comment"):
+                comment_lines += child.text.decode("utf-8", errors="replace").count("\n") + 1
+
+            if ntype == "function_declaration":
+                name = _text(_child_by_type(child, "identifier"))
+                params = _text(_child_by_type(child, "parameter_list"))
+                functions.append(f"{name}{params}")
+            elif ntype == "type_declaration":
+                spec = _child_by_type(child, "type_spec")
+                name = _text(_child_by_type(spec, "type_identifier")) if spec else ""
+                classes.append({"name": name or _text(child)[:60], "methods": []})
+            elif ntype == "import_declaration":
+                imports.append(child.text.decode("utf-8", errors="replace").strip())
+
+            _walk(child)
+
+    _walk(root)
+
+    source_text = source.decode("utf-8", errors="replace")
+    line_count = len(source_text.split("\n"))
+    code_lines = max(1, line_count - comment_lines)
+
+    return {
+        "language": "go",
+        "functions": functions[:50],
+        "classes": classes[:30],
+        "imports": imports[:30],
+        "line_count": line_count,
+        "has_docstrings": False,
+        "has_comments": comment_lines > 0,
+        "comment_to_code_ratio": round(comment_lines / code_lines, 2),
+    }
+
+
+# ---------------------------------------------------------------------------
+# Language handler registry
+# ---------------------------------------------------------------------------
+
+_LANGUAGE_HANDLERS = {
+    "python": _parse_python,
+    "javascript": _parse_javascript,
+    "rust": _parse_rust,
+    "go": _parse_go,
+}
+
+
+# ---------------------------------------------------------------------------
+# Public API
+# ---------------------------------------------------------------------------
+
+def parse_structure(path):
+    """Parse a source file and return its structural skeleton as a JSON string.
+
+    Takes an absolute path. Returns a JSON string of the structure dict,
+    or an error string if parsing fails or the language is unsupported.
+    """
+    if not os.path.isfile(path):
+        return f"Error: '{path}' is not a file."
+
+    ext = os.path.splitext(path)[1].lower()
+    ts = _get_ts_parser(ext)
+    if ts is None:
+        return (f"Error: no grammar for extension '{ext}'. "
+                f"Supported: {', '.join(sorted(_TS_LANGUAGES.keys()))}")
+
+    parser, lang_name = ts
+
+    handler = _LANGUAGE_HANDLERS.get(lang_name)
+    if handler is None:
+        return f"Error: no handler for language '{lang_name}'."
+
+    try:
+        with open(path, "rb") as f:
+            source = f.read()
+    except OSError as e:
+        return f"Error reading file: {e}"
+
+    tree = parser.parse(source)
+    result = handler(tree.root_node, source)
+    return json.dumps(result, indent=2)