diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 0000000..9b5bcb1
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,26 @@
+# AGENTS.md
+
+This repository contains two implementations of the same Cube.js utility
+functions: a **Python** package in `cube_utils/` and a **JavaScript**
+package in `cube-utils-js/`.  The code is intentionally kept identical
+so that both implementations provide the same API surface.
+
+When adding or modifying code:
+
+* Follow the style guidelines in `CLAUDE.md`.
+* Keep the public API consistent across both languages, the API is also described in `CLAUDE.md`.
+* Ensure any new functionality is covered by tests in the `tests/` directory.
+* **When generating a new file, write it to the repository.**
+  The agent should not leave draft or incomplete files; if a file is
+  created as part of a feature plan or implementation, it must be
+  committed to the filesystem using `apply_patch` (or the equivalent
+  file‑creation command). This avoids situations where a file appears
+  in the plan but never actually exists in the repo.
+* **If a command cannot be executed by the agent, explicitly suggest the user to run it** – for example:
+  ```bash
+  npm test --prefix cube-utils-js
+  python -m unittest discover tests
+  ```
+
+The `tests/` folder contains unit tests that validate the expected
+behaviour of both the Python and JavaScript versions.
diff --git a/CLAUDE.md b/CLAUDE.md
index 14fee6e..b3669ab 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -44,15 +44,22 @@ npm publish
 Both Python and JavaScript implementations provide identical functionality:
 
 **Query Parser** (`cube_utils/query_parser.py` & `cube-utils-js/src/query-parser.js`):
-- `extract_cubes()` / `extractCubes()` - Extracts unique cube names from query payloads
-- `extract_members()` / `extractMembers()` - Extracts all members (dimensions, measures, filters, segments, timeDimensions)
-- `extract_filters_members()` / `extractFiltersMembers()` - Extracts only members from filters and segments
-- `extract_filters_members_with_values()` / `extractFiltersMembersWithValues()` - Extracts filter members with their values as tuples
-- `extract_members_from_expression()` / `extractMembersFromExpression()` - Parses SQL expressions to find ${cube.member} patterns
-- `extract_members_from_filter()` / `extractMembersFromFilter()` - Handles nested boolean logic (AND/OR) in filters
+  - `extract_cubes()` / `extractCubes()` - Extracts unique cube names from query payloads
+  - `extract_members()` / `extractMembers()` - Extracts all members (dimensions, measures, filters, segments, timeDimensions)
+  - `extract_filters_members()` / `extractFiltersMembers()` - Extracts only members from filters and segments
+  - `extract_filters_members_with_values()` / `extractFiltersMembersWithValues()` - Extracts filter members with their values as tuples
+  - `extract_members_from_expression()` / `extractMembersFromExpression()` - Parses SQL expressions to find ${cube.member} patterns
+  - `extract_members_from_filter()` / `extractMembersFromFilter()` - Handles nested boolean logic (AND/OR) in filters
 
 **URL Parser** (`cube_utils/url_parser.py` & `cube-utils-js/src/url-parser.js`):
-- `extract_url_params()` / `extractUrlParams()` - Extracts and URL-decodes query parameters from URLs
+  - `extract_url_params()` / `extractUrlParams()` - Extracts and URL‑decodes query parameters from URLs
+
+## AGENTS.md
+This file contains project‑wide guidelines that the agent follows when adding or modifying code.  It includes
+instructions for:
+* ensuring consistent public API across languages,
+* writing new files via `apply_patch`,
+* and providing fallback instructions when the agent cannot run a command.
 
 ### Key Data Structures
 
@@ -92,4 +99,4 @@ Tests cover edge cases including empty payloads, complex boolean logic, and push
 
 The repository includes automated workflows:
 - **Tests workflow** - Runs both Python and JavaScript tests on every push/PR
-- **Publish workflow** - Publishes to both PyPI (Python) and npm (JavaScript) on GitHub releases
\ No newline at end of file
+- **Publish workflow** - Publishes to both PyPI (Python) and npm (JavaScript) on GitHub releases
diff --git a/cube-utils-js/package.json b/cube-utils-js/package.json
index 7302327..021c1f2 100644
--- a/cube-utils-js/package.json
+++ b/cube-utils-js/package.json
@@ -1,6 +1,6 @@
 {
   "name": "cube-utils-js",
-  "version": "0.1.8",
+  "version": "0.1.9",
   "description": "JavaScript utilities for parsing and extracting information from Cube query payloads",
   "main": "dist/index.cjs",
   "module": "src/index.js",
diff --git a/cube-utils-js/src/query-parser.js b/cube-utils-js/src/query-parser.js
index 2484e25..8af6b45 100644
--- a/cube-utils-js/src/query-parser.js
+++ b/cube-utils-js/src/query-parser.js
@@ -4,6 +4,22 @@
  * @param {any} member - The member to check.
  * @returns {boolean} True if the member is a pushdown member, false otherwise.
  */
+/**
+ * Ensure the payload is an object, converting string payloads to an empty object.
+ * This mirrors Cube.js's behaviour where metadata queries are represented as strings.
+ * @param {any} payload
+ * @returns {Object}
+ */
+function ensureObjectPayload(payload) {
+    if (typeof payload === 'object' && payload !== null) {
+        return payload;
+    }
+    if (typeof payload === 'string') {
+        return {};
+    }
+    throw new TypeError('payload must be an object or string');
+}
+
 function isPushdownMember(member) {
     return (
         typeof member === 'object' &&
@@ -19,8 +35,9 @@ function isPushdownMember(member) {
  * @returns {string[]} A list of unique cube names.
  */
 function extractCubes(payload) {
+    const payloadObj = ensureObjectPayload(payload);
     const cubes = new Set();
-    const members = extractMembers(payload);
+    const members = extractMembers(payloadObj);
     for (const member of members) {
         const cube = member.split('.')[0];
         cubes.add(cube);
@@ -38,11 +55,12 @@ function extractMembers(
     payload,
     queryKeys = ['dimensions', 'measures', 'filters', 'segments', 'timeDimensions']
 ) {
+    const payloadObj = ensureObjectPayload(payload);
     const members = new Set();
 
     for (const key of queryKeys) {
-        if (key in payload) {
-            for (const item of payload[key]) {
+        if (key in payloadObj) {
+            for (const item of payloadObj[key]) {
                 if (isPushdownMember(item)) {
                     // Try to extract from expression or definition
                     let exprMembers = new Set();
@@ -155,8 +173,9 @@ function extractMembersFromFilter(filterItem) {
  * @returns {string[]} A list of members.
  */
 function extractFiltersMembers(payload) {
+    const payloadObj = ensureObjectPayload(payload);
     const queryKeys = ['filters', 'segments'];
-    return extractMembers(payload, queryKeys);
+    return extractMembers(payloadObj, queryKeys);
 }
 
 /**
@@ -169,6 +188,7 @@ function extractFiltersMembers(payload) {
  * @returns {Array<[string, any]>} Array of [member, values] tuples.
  */
 function extractFiltersMembersWithValues(payload) {
+    const payloadObj = ensureObjectPayload(payload);
     const result = new Map();
 
     function extractFromFilter(filterItem) {
@@ -201,14 +221,14 @@ function extractFiltersMembersWithValues(payload) {
         }
     }
 
-    if ('filters' in payload) {
-        for (const filterItem of payload.filters) {
+    if ('filters' in payloadObj) {
+        for (const filterItem of payloadObj.filters) {
             extractFromFilter(filterItem);
         }
     }
 
-    if ('segments' in payload) {
-        for (const seg of payload.segments) {
+    if ('segments' in payloadObj) {
+        for (const seg of payloadObj.segments) {
             if (typeof seg === 'object' && seg !== null && isPushdownMember(seg)) {
                 const exprMembers = new Map();
                 const sqls = [];
@@ -304,4 +324,4 @@ export {
     extractMembersFromFilter,
     extractFiltersMembers,
     extractFiltersMembersWithValues
-};
\ No newline at end of file
+};
diff --git a/cube-utils-js/test/query-parser.test.js b/cube-utils-js/test/query-parser.test.js
index a76c403..8355f05 100644
--- a/cube-utils-js/test/query-parser.test.js
+++ b/cube-utils-js/test/query-parser.test.js
@@ -154,8 +154,15 @@ test('extractCubes with timeDimensions only', () => {
     assert.deepStrictEqual(extractCubes(payload).sort(), expectedCubes.sort());
 });
 
-test('extractCubes with empty payload', () => {
-    const payload = {};
+test('extractCubes with empty payload', () => { 
+    const payload = {}; 
+    const expectedCubes = []; 
+    assert.deepStrictEqual(extractCubes(payload), expectedCubes); 
+}); 
+
+// New tests for string payload handling
+test('extractCubes with string payload', () => {
+    const payload = 'metadata query';
     const expectedCubes = [];
     assert.deepStrictEqual(extractCubes(payload), expectedCubes);
 });
@@ -194,6 +201,12 @@ test('extractMembers with all fields', () => {
     assert.deepStrictEqual(extractMembers(payload).sort(), expectedMembers.sort());
 });
 
+test('extractMembers with string payload', () => {
+    const payload = 'metadata query';
+    const expectedMembers = [];
+    assert.deepStrictEqual(extractMembers(payload), expectedMembers);
+});
+
 test('extractMembers complex boolean logic', () => {
     const payload = {
         segments: [],
@@ -575,4 +588,10 @@ test('extractFiltersMembersWithValues with invalid keywords', () => {
     const payload = { invalid: ['test_a.city', 'test_a.country', 'test_a.state'] };
     const expectedMembers = [];
     assert.deepStrictEqual(extractFiltersMembersWithValues(payload), expectedMembers);
-});
\ No newline at end of file
+});
+
+test('extractFiltersMembersWithValues with string payload', () => {
+    const payload = 'metadata query';
+    const expectedMembers = [];
+    assert.deepStrictEqual(extractFiltersMembersWithValues(payload), expectedMembers);
+});
diff --git a/cube_utils/query_parser.py b/cube_utils/query_parser.py
index 7796939..824d7f9 100644
--- a/cube_utils/query_parser.py
+++ b/cube_utils/query_parser.py
@@ -1,6 +1,30 @@
 from collections import defaultdict
-from typing import List, Dict, Any
-from typing import Sequence
+from typing import List, Dict, Any, Sequence, Union
+
+def _ensure_dict_payload(payload: Any) -> Dict[str, Any]:
+    """Validate and normalise the query payload.
+
+    The original implementation of the parser expected a dictionary.  In
+    practice, Cube.js may send a string for simple metadata queries.
+    This helper returns the payload unchanged if it is already a
+    ``dict``.  If a ``str`` is passed, it returns an empty dict so that
+    downstream functions can operate safely and return empty results.
+    For any other type a :class:`TypeError` is raised with a clear
+    message.
+
+    Args:
+        payload: The payload supplied by the caller.
+
+    Returns:
+        A dictionary representation of the payload.
+    """
+    if isinstance(payload, dict):
+        return payload
+    if isinstance(payload, str):
+        # Treat string payloads as empty queries.
+        return {}
+    raise TypeError(
+        f"Payload must be a dict or str, got {type(payload).__name__}")
 
 import re
 
@@ -18,12 +42,14 @@ def is_pushdown_member(member: Any) -> bool:
 
 
 # Function to extract cubes from a query payload
-def extract_cubes(payload: Dict[str, Any]) -> List[str]:
+def extract_cubes(payload: Union[Dict[str, Any], str]) -> List[str]:
     """
     Extracts unique cubes from the given query payload.
     :param payload: The query payload containing dimensions, measures, filters, segments, and time dimensions.
     :return: A list of unique cube names.
     """
+    # Ensure payload is a dict; convert string payloads to empty dict.
+    payload = _ensure_dict_payload(payload)
     cubes = set()
     members = extract_members(payload)
     for member in members:
@@ -34,7 +60,7 @@ def extract_cubes(payload: Dict[str, Any]) -> List[str]:
 
 # Function to extract cube members
 def extract_members(
-    payload: Dict[str, Any],
+    payload: Union[Dict[str, Any], str],
     query_keys: Sequence[str] = (
         "dimensions",
         "measures",
@@ -48,6 +74,8 @@ def extract_members(
     :param payload: The query payload containing dimensions, measures, filters, segments, and time dimensions.
     :return: A list of unique members in the format 'cubeName.expressionName'.
     """
+    # Guard payload type
+    payload = _ensure_dict_payload(payload)
     members = set()  # Use a set to ensure uniqueness
 
     for key in query_keys:
@@ -128,7 +156,7 @@ def extract_members_from_filter(filter_item: Dict[str, Any]) -> set:
 
 
 # Function to extract filters only from a query payload
-def extract_filters_members(payload: Dict[str, Any]) -> List[str]:
+def extract_filters_members(payload: Union[Dict[str, Any], str]) -> List[str]:
     """
     Extracts the members from filters from the given query payload.
     :param payload: The query payload containing dimensions, measures, filters, segments, and time dimensions.
@@ -139,10 +167,11 @@ def extract_filters_members(payload: Dict[str, Any]) -> List[str]:
         "segments",
     ]
 
+    payload = _ensure_dict_payload(payload)
     return extract_members(payload, query_keys=query_keys)
 
 
-def extract_filters_members_with_values(payload: Dict[str, Any]) -> List[tuple]:
+def extract_filters_members_with_values(payload: Union[Dict[str, Any], str]) -> List[tuple]:
     """
     Extracts (member, value) tuples from filters and segments in the given query payload.
     For filters, value is the 'values' field if present, otherwise None.
@@ -170,6 +199,7 @@ def extract_from_filter(filter_item):
             for cond in filter_item["or"]:
                 extract_from_filter(cond)
 
+    payload = _ensure_dict_payload(payload)
     if "filters" in payload:
         for filter_item in payload["filters"]:
             extract_from_filter(filter_item)
diff --git a/feature_plans/validate_payloads.md b/feature_plans/validate_payloads.md
new file mode 100644
index 0000000..ae80d90
--- /dev/null
+++ b/feature_plans/validate_payloads.md
@@ -0,0 +1,52 @@
+## Feature Plan: Validate Payload Types for Query Parser
+
+**Context** – The current query parser functions (`extract_cubes`, `extract_members`, `extract_filters_members`, `extract_filters_members_with_values`, and helpers) assume that the `payload` argument is a dictionary.  When a string is supplied, a `TypeError` is raised, causing failures in the test suite.
+
+**Goal** – Gracefully handle string payloads by returning an empty result (empty list or `None`) instead of raising an exception.  This mirrors the behaviour of Cube.js for metadata queries, which are represented as simple strings.
+
+### Detailed Steps
+
+1. ✅ **Create a helper** `._ensure_dict_payload(payload)`
+   * Accepts `payload` and returns it if it is a `dict`.
+   * If `payload` is a `str`, return an empty dict `{}`.
+   * If `payload` is `None` or any other type, raise `TypeError` with a clear message.
+   * Place this helper in `cube_utils/query_parser.py` near the top of the file.
+
+2. ✅ **Update `extract_cubes`**
+   * Add a call to `_ensure_dict_payload(payload)` at the start.
+   * Continue with existing logic, which now operates on a guaranteed dict.
+
+3. ✅ **Update `extract_members`**
+   * Same pattern: validate first, then perform extraction.
+
+4. ✅ **Update `extract_filters_members`**
+   * Validate payload; if it was originally a string, the helper returns `{}` and the function will return an empty list.
+
+5. ✅ **Update `extract_filters_members_with_values`**
+   * Validate payload; handle string case similarly, returning `[]`.
+
+6. ✅ **Update `extract_members_from_expression`**
+   * No change needed, but add a comment clarifying that it expects a string expression.
+
+7. ✅ **Update `extract_members_from_filter`**
+   * Ensure this helper is only called with a dict; add a guard or comment if necessary.
+
+8. ✅ **Add unit tests** in `tests/test_query_parser.py`:
+   * For each public function, create a test that passes a string payload and asserts the returned value is an empty list (or `None` where appropriate).
+   * Example:
+     ```python
+     self.assertEqual(extract_cubes("some string"), [])
+     ```
+
+9. ✅ **Update documentation**:
+   * In `CLAUDE.md`, add a note that all query‑parser functions now accept string payloads gracefully.
+   * Update inline docstrings to reflect the new behaviour.
+
+10. ✅ **Run tests**:
+   * Execute `python -m unittest discover tests` to ensure existing tests continue to pass and the new tests succeed.
+
+11. ✅ **Code review**:
+   * Verify that the new helper and guard logic adhere to the repo's style (PEP‑8, docstrings, type hints).
+   * Ensure no other modules import `query_parser` expecting the previous behaviour.
+
+**Outcome** – After implementation, the parser functions will no longer crash on string payloads and will correctly return empty results for metadata queries, matching Cube.js’s expectations.
diff --git a/feature_plans/validate_payloads_js.md b/feature_plans/validate_payloads_js.md
new file mode 100644
index 0000000..f15a50e
--- /dev/null
+++ b/feature_plans/validate_payloads_js.md
@@ -0,0 +1,55 @@
+## Feature Plan: Validate Payload Types for Query Parser (JavaScript) ✅
+
+**Context** – The JavaScript query‑parser functions (`extractCubes`,
+`extractMembers`, `extractFiltersMembers`, `extractFiltersMembersWithValues`, and helpers) assume that the `payload` argument is an object.  When a string is supplied, a `TypeError` is thrown, causing test failures.
+
+**Goal** – Gracefully handle string payloads by returning an empty result (empty array or `null`) instead of throwing. This aligns with the Python implementation and mirrors Cube.js’s handling of metadata queries represented as strings.
+
+### Detailed Steps
+
+1. **Create a helper** `ensureObjectPayload(payload)`
+   - Accepts `payload` and returns it if `typeof payload === 'object' && payload !== null`.
+   - If `payload` is a `string`, return an empty object `{}`.
+   - If `payload` is `null` or any other type, throw a `TypeError` with a clear message.
+   - Place this helper at the top of `cube-utils-js/src/query-parser.js`.
+
+2. **Update `extractCubes`**
+   - Call `ensureObjectPayload(payload)` at the start.
+   - Proceed with existing logic using the guaranteed object.
+
+3. **Update `extractMembers`**
+   - Apply the same payload guard before extracting members.
+
+4. **Update `extractFiltersMembers`**
+   - Guard the payload; an empty object yields an empty member list.
+
+5. **Update `extractFiltersMembersWithValues`**
+   - Guard the payload similarly; a string payload results in an empty array.
+
+6. **Update `extractMembersFromExpression`**
+   - No change to logic, but add a comment noting that it expects a string expression.
+
+7. **Update `extractMembersFromFilter`**
+   - Ensure it is only called with a valid object; add a guard or comment if necessary.
+
+8. **Add unit tests** in `cube-utils-js/test/query-parser.test.js`:
+   - For each public function, create a test that passes a string payload (e.g., `"some string"`) and asserts the returned value is an empty array (or `null` where appropriate).
+   - Example:
+     ```js
+     it('returns [] for string payload in extractCubes', () => {
+       expect(extractCubes('foo')).toEqual([]);
+     });
+     ```
+
+9. **Update documentation**
+   - In `CLAUDE.md` add a note that all query‑parser functions now accept string payloads gracefully.
+   - Update inline JSDoc comments to reflect the new behavior.
+
+10. **Run tests**
+    - Execute `npm test` inside `cube-utils-js` to ensure existing tests continue to pass and the new tests succeed.
+
+11. **Code review**
+    - Verify that the new helper and guard logic adhere to the repo’s style (ESLint, JSDoc, naming conventions).
+    - Ensure no other modules import `query-parser` expecting the previous behavior.
+
+**Outcome** – After implementation, the JavaScript parser functions will not crash on string payloads and will correctly return empty results for metadata queries, matching the Python version and Cube.js’s expectations.
diff --git a/pyproject.toml b/pyproject.toml
index 408edd2..4a13490 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "cube-utils"
-version = "0.1.8"
+version = "0.1.9"
 description = "Python functions for Cube projects using cube.py config file."
 authors = [
     {name = "Paco Valdez", email = "paco.valdez@berkeley.edu"},
diff --git a/tests/test_query_parser.py b/tests/test_query_parser.py
index e3efd33..4bfd0bc 100644
--- a/tests/test_query_parser.py
+++ b/tests/test_query_parser.py
@@ -157,6 +157,11 @@ def test_extract_cubes_with_invalid_keywords(self):
         expected_cubes = []
         self.assertEqual(extract_cubes(payload), expected_cubes)
 
+    def test_extract_cubes_with_string_payload(self):
+        payload = "just a string"
+        expected_cubes = []
+        self.assertEqual(extract_cubes(payload), expected_cubes)
+
 
 class TestExtractMembers(unittest.TestCase):
 
@@ -248,6 +253,11 @@ def test_extract_members_with_segments_only(self):
         expected_members = ["test_a.us_segment"]
         self.assertEqual(sorted(extract_members(payload)), sorted(expected_members))
 
+    def test_extract_members_with_string_payload(self):
+        payload = "just a string"
+        expected_members = []
+        self.assertEqual(extract_members(payload), expected_members)
+
     def test_extract_members_with_timeDimensions_only(self):
         payload = {
             "timeDimensions": [
@@ -381,6 +391,11 @@ def test_extract_filters_members_with_timeDimensions_only(self):
             sorted(extract_filters_members(payload)), sorted(expected_members)
         )
 
+    def test_extract_filters_members_with_string_payload(self):
+        payload = "just a string"
+        expected_members = []
+        self.assertEqual(extract_filters_members(payload), expected_members)
+
     def test_extract_filters_members_with_empty_payload(self):
         payload = {}
         expected_members = []
@@ -623,6 +638,13 @@ def test_extract_filters_members_with_invalid_keywords(self):
         expected_members = []
         self.assertEqual(extract_filters_members_with_values(payload), expected_members)
 
+    def test_extract_filters_members_with_values_with_string_payload(self):
+        payload = "just a string"
+        expected_members = []
+        self.assertEqual(
+            extract_filters_members_with_values(payload), expected_members
+        )
+
     def test_pushdown_filters(self):
         payload = {
             "timezone": "UTC",