diff --git a/README.md b/README.md
index 1b152e6..8c7d47a 100644
--- a/README.md
+++ b/README.md
@@ -92,7 +92,7 @@ Use query parameters:
 | Parameter   | Description |
 | ----------- | ----------- |
 | **`url`**   | Required. Address of the JSON document (`http` or `https`). Must be URL-encoded in the query string. |
-| **`query`** | Required. [JSONPath](https://goessner.net/articles/JsonPath/) (e.g. `$.items[0].metrics.pct`) or dot form from the root (e.g. `items.0.metrics.pct`). |
+| **`query`** | Required. [JSONPath](https://goessner.net/articles/JsonPath/) (e.g. `$.items[0].metrics.pct`) or dot form from the root (e.g. `items.0.metrics.pct`). Filter expressions are supported, so you can look up a value by a sibling field instead of a hardcoded index — e.g. `$.progress[?(@.data.language.name=='Spanish')].data.translationProgress`. |
 | **`cache`** | Optional. `Cache-Control` max-age in seconds. Default: none (header not set unless provided and `> 0`). |
 
 Any other parameters from the table above (`title`, `scale`, `style`, …) apply the same way as on `/{number}/`.
diff --git a/app.py b/app.py
index 2c30030..afca386 100644
--- a/app.py
+++ b/app.py
@@ -8,8 +8,8 @@
 from urllib.request import HTTPRedirectHandler, Request, build_opener
 
 from flask import Flask, make_response, redirect, render_template, request
-from jsonpath_ng import parse
 from jsonpath_ng.exceptions import JsonPathParserError
+from jsonpath_ng.ext import parse
 
 app = Flask(__name__)
 
@@ -100,7 +100,13 @@ def normalize_jsonpath_query(selector):
   """
   Normalize a path selector into jsonpath-ng syntax or dot form from the root.
 
-  Examples: ``$.items[0].metrics.pct`` or ``items.0.metrics.pct``.
+  Accepts full JSONPath (including filter expressions) when prefixed with ``$``,
+  or a simple dot/index form from the root.
+
+  Examples:
+    - ``$.items[0].metrics.pct``
+    - ``items.0.metrics.pct``
+    - ``$.progress[?(@.data.language.name=='Spanish')].data.translationProgress``
   """
   q = (selector or "").strip()
   if not q:
@@ -439,8 +445,9 @@ def get_progress_svg_dynamic_json():
   """
   Load progress from a remote JSON `url` and a `query` into that document.
 
-  `query` is a jsonpath-ng expression (e.g. $.items[0].metrics.pct) or dot form
-  from the root (e.g. items.0.metrics.pct).
+  `query` is a jsonpath-ng expression (e.g. $.items[0].metrics.pct), a dot form
+  from the root (e.g. items.0.metrics.pct), or a filter expression
+  (e.g. $.progress[?(@.data.language.name=='Spanish')].data.translationProgress).
   Optional `cache` sets Cache-Control max-age in seconds.
   Other params match /N/ (title, scale, width, style, …).
   """
diff --git a/test_api.py b/test_api.py
index 15fa8c1..c7e6084 100644
--- a/test_api.py
+++ b/test_api.py
@@ -97,6 +97,42 @@ def test_dynamic_json_jsonpath_dollar(mock_fetch, client):
     assert b"42" in response.data
 
 
+@patch("app.fetch_json_document")
+def test_dynamic_json_filter_expression_by_name(mock_fetch, client):
+    mock_fetch.return_value = {
+        "progress": [
+            {"data": {"language": {"name": "Arabic"}, "translationProgress": 5}},
+            {"data": {"language": {"name": "Spanish"}, "translationProgress": 87}},
+        ],
+    }
+    response = client.get(
+        "/dynamic/json/",
+        query_string={
+            "url": "https://example.com/stats.json",
+            "query": "$.progress[?(@.data.language.name=='Spanish')].data.translationProgress",
+        },
+    )
+    assert response.status_code == 200
+    assert b"87" in response.data
+
+
+@patch("app.fetch_json_document")
+def test_dynamic_json_filter_expression_no_match_returns_422(mock_fetch, client):
+    mock_fetch.return_value = {
+        "progress": [
+            {"data": {"language": {"name": "Arabic"}, "translationProgress": 5}},
+        ],
+    }
+    response = client.get(
+        "/dynamic/json/",
+        query_string={
+            "url": "https://example.com/stats.json",
+            "query": "$.progress[?(@.data.language.name=='Klingon')].data.translationProgress",
+        },
+    )
+    assert response.status_code == 422
+
+
 @patch("app.fetch_json_document")
 def test_dynamic_json_percent_suffix_string(mock_fetch, client):
     mock_fetch.return_value = {"approvalProgress": "73%"}