diff --git a/CHANGELOG.md b/CHANGELOG.md
index 73f6da7..57be826 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,11 @@ semantic versioning.
 
 ### Fixed
 
+- Refactor response_template parsing to use finite state machine when processing
+  templates adding additional flexibility such as the use of nested fields. Added
+  support for shlink to External_Data configuration. Added url_shortener filter and
+  if_notempty filter to response_template.
+
 - `path` no longer answers "No path information available in current message" on a
   busy mesh (#255). Verifying a channel message against the RF cache only ever
   checked the newest row, which assumes the RF log row and the decoded CHAN event
diff --git a/docs/path-command-config.md b/docs/path-command-config.md
index 4688582..c0324d6 100644
--- a/docs/path-command-config.md
+++ b/docs/path-command-config.md
@@ -27,6 +27,17 @@ These options only affect the **path** command’s reply text and whether repeat
 reply_prefix = "{path_distance|prefix_if_nonempty:📏 }\n"
 ```
 - `hops_min:N` clears a field unless the message actually travelled at least N hops. `{path_distance}` renders `N/A` on a direct message, which `prefix_if_nonempty` treats as a value, so gate it first: `{path_distance|hops_min:1|prefix_if_nonempty:📏 }`. Unlike `pathbytes_min:N`, which asks how the path is *encoded*, this keeps a measurable one-byte multi-hop path.
+- `if_notempty:LITERAL` renders `LITERAL` when the value is non-empty after prior filters, and clears entirely otherwise — the opposite pairing of `prefix_if_nonempty`, useful when the whole output should be a fixed (or field-built) literal rather than the value with a label prepended. Since `{packet_hash}` is empty whenever RF correlation fails, gating on it hides the whole clause instead of printing a broken link:
+
+```ini
+reply_prefix = {packet_hash|if_notempty:"https://scope.example.net/#/packets/{packet_hash}"}
+```
+  The `LITERAL` argument may itself be a double-quoted string containing nested `{field}` placeholders (expanded before the filter runs), so the link above still carries the packet hash even though the field being gated on (`packet_hash`) and the field inside the literal are the same one.
+- `shorten_url` runs the value through the shared shortener configured under `[External_Data]` (`short_url_website`, `short_url_website_service` — `gd` for v.gd/is.gd-compatible or `shlink`, and `short_url_website_api_key` where required). It falls back to the original, unshortened value if shortening fails or isn't configured, so a clause never silently disappears because of a network error. Chain it after building the link so only the final URL is sent over RF:
+
+```ini
+reply_prefix = {packet_hash|if_notempty:"https://scope.example.net/#/packets/{packet_hash}"|shorten_url}
+```
 
 **`minimum_path_bytes`** (integer `0`–`3`, default `0`)
 
diff --git a/modules/response_template.py b/modules/response_template.py
index 2e831a2..ff62cc6 100644
--- a/modules/response_template.py
+++ b/modules/response_template.py
@@ -13,8 +13,8 @@ from __future__ import annotations
 
 from typing import Any, Callable
 
-from .utils import message_hop_count, message_path_bytes_per_hop
 from .url_shortener import shorten_url_sync
+from .utils import message_hop_count, message_path_bytes_per_hop
 
 FilterFn = Callable[[str, dict[str, Any], str], str]
 
diff --git a/modules/url_shortener.py b/modules/url_shortener.py
index 9f2bb51..b76de44 100644
--- a/modules/url_shortener.py
+++ b/modules/url_shortener.py
@@ -107,7 +107,6 @@ def _build_create_gd_url(long_url: str, base: str, api_key: str) -> str:
 def _build_create_shlink_url(long_url: str, base: str, api_key: str) -> str:
     from urllib.parse import urlparse, urlunparse
 
-    encoded = quote(long_url, safe="")
     root = _normalize_base(base)
     if "://" not in root:
         root = f"https://{root}"
@@ -206,30 +205,32 @@ def shorten_url_sync(
         ).strip()
         base = _normalize_base(base)
 
-        if base != "" and api_key != "":
-            if service == "shlink":
-                return _shorten_url_with_shlink(
-                    url_str,
-                    base,
-                    api_key,
-                    session=session,
-                    timeout=timeout,
-                    logger=logger,
-                )
-            else:
-                return _shorten_url_with_gd(
-                    url_str,
-                    base,
-                    api_key,
-                    session=session,
-                    timeout=timeout,
-                    logger=logger,
-                )
-        else:
-            if logger:
-                logger.warning(
-                    "Short URL base and API key are empty; some services may reject requests."
-                )
+        if service == "shlink":
+            if not api_key:
+                if logger:
+                    logger.warning(
+                        "short_url_website_service=shlink requires short_url_website_api_key; skipping."
+                    )
+                return ""
+            return _shorten_url_with_shlink(
+                url_str,
+                base,
+                api_key,
+                session=session,
+                timeout=timeout,
+                logger=logger,
+            )
+
+        # v.gd / is.gd-compatible: api_key is optional (unused for the public hosts,
+        # only appended for self-hosted alternates via _host_allows_key_in_query).
+        return _shorten_url_with_gd(
+            url_str,
+            base,
+            api_key,
+            session=session,
+            timeout=timeout,
+            logger=logger,
+        )
 
     except Exception as e:
         if logger:
diff --git a/tests/test_url_shortener.py b/tests/test_url_shortener.py
index 275cfdd..8829a91 100644
--- a/tests/test_url_shortener.py
+++ b/tests/test_url_shortener.py
@@ -1,6 +1,7 @@
 """Unit tests for modules.url_shortener."""
 
 import configparser
+import json
 from unittest.mock import MagicMock, patch
 
 import pytest
@@ -8,7 +9,8 @@ import requests
 
 from modules.url_shortener import (
     DEFAULT_SHORT_URL_BASE,
-    _build_create_url,
+    _build_create_gd_url,
+    _build_create_shlink_url,
     _coerce_url_string,
     shorten_url_sync,
 )
@@ -22,23 +24,42 @@ def _minimal_config(**external_data):
     return c
 
 
-class TestBuildCreateUrl:
+class TestBuildCreateGdUrl:
     def test_vgd_no_key_in_query(self):
-        u = _build_create_url("http://example.com/path?q=1", "https://v.gd", "secret")
+        u = _build_create_gd_url("http://example.com/path?q=1", "https://v.gd", "secret")
         assert "key=" not in u
         assert "format=simple" in u
         assert "url=http" in u
 
     def test_custom_host_appends_key_when_set(self):
-        u = _build_create_url("http://a.com", "https://short.example/api", "k1")
+        u = _build_create_gd_url("http://a.com", "https://short.example/api", "k1")
         assert "key=k1" in u
 
     def test_is_gd_no_key_in_query(self):
-        u = _build_create_url("http://a.com", "https://is.gd", "secret")
+        u = _build_create_gd_url("http://a.com", "https://is.gd", "secret")
         assert "key=" not in u
         assert "create.php" in u
 
 
+class TestBuildCreateShlinkUrl:
+    def test_appends_rest_v3_short_urls_path(self):
+        u = _build_create_shlink_url("http://a.com", "https://short.example", "k1")
+        assert u == "https://short.example/rest/v3/short-urls"
+
+    def test_strips_trailing_slash_on_base(self):
+        u = _build_create_shlink_url("http://a.com", "https://short.example/", "k1")
+        assert u == "https://short.example/rest/v3/short-urls"
+
+    def test_bare_hostname_gets_https_scheme(self):
+        u = _build_create_shlink_url("http://a.com", "short.example", "k1")
+        assert u == "https://short.example/rest/v3/short-urls"
+
+    def test_api_key_never_appears_in_the_url(self):
+        """Shlink authenticates via the X-Api-Key header, not a query param."""
+        u = _build_create_shlink_url("http://a.com", "https://short.example", "super-secret")
+        assert "super-secret" not in u
+
+
 class TestCoerceUrlString:
     def test_dict_href(self):
         assert _coerce_url_string({"href": "https://a.com/x"}) == "https://a.com/x"
@@ -85,6 +106,21 @@ class TestShortenUrlSync:
         assert call_url.startswith("https://v.gd/create.php")
         assert "format=simple" in call_url
 
+    def test_default_gd_service_needs_no_api_key(self):
+        """Regression: v.gd/is.gd are documented as keyless (config.ini.example);
+        the default `gd` service must not require short_url_website_api_key."""
+        cfg = _minimal_config(short_url_website="https://v.gd")
+        assert cfg.get("External_Data", "short_url_website_api_key", fallback="") == ""
+        mock_resp = MagicMock()
+        mock_resp.ok = True
+        mock_resp.text = "https://v.gd/nokey\n"
+        session = MagicMock()
+        session.get.return_value = mock_resp
+
+        out = shorten_url_sync("http://a.com", config=cfg, session=session)
+        assert out == "https://v.gd/nokey"
+        session.get.assert_called_once()
+
     def test_error_line_returns_empty(self):
         cfg = _minimal_config()
         mock_resp = MagicMock()
@@ -170,6 +206,17 @@ class TestShortenUrlSync:
         call_url = session.get.call_args[0][0]
         assert call_url.startswith(DEFAULT_SHORT_URL_BASE)
 
+    def test_service_option_is_case_insensitive(self):
+        cfg = _minimal_config(short_url_website="https://v.gd", short_url_website_service="GD")
+        mock_resp = MagicMock()
+        mock_resp.ok = True
+        mock_resp.text = "https://v.gd/caseok"
+        session = MagicMock()
+        session.get.return_value = mock_resp
+
+        out = shorten_url_sync("http://a.com", config=cfg, session=session)
+        assert out == "https://v.gd/caseok"
+
     @patch("modules.url_shortener.requests.get")
     def test_no_session_uses_requests_get(self, mock_get):
         cfg = _minimal_config(short_url_website="https://v.gd")
@@ -183,6 +230,103 @@ class TestShortenUrlSync:
         mock_get.assert_called_once()
 
 
+class TestShortenUrlSyncShlink:
+    def _shlink_config(self, **overrides):
+        defaults = {
+            "short_url_website_service": "shlink",
+            "short_url_website": "https://short.example",
+            "short_url_website_api_key": "test-api-key",
+        }
+        defaults.update(overrides)
+        return _minimal_config(**defaults)
+
+    def test_success_returns_short_url(self):
+        cfg = self._shlink_config()
+        mock_resp = MagicMock()
+        mock_resp.json.return_value = {"shortUrl": "https://short.example/abc123"}
+        session = MagicMock()
+        session.post.return_value = mock_resp
+
+        out = shorten_url_sync("https://example.com/long/path", config=cfg, session=session)
+
+        assert out == "https://short.example/abc123"
+        session.post.assert_called_once()
+
+    def test_posts_to_rest_v3_short_urls_with_api_key_header(self):
+        cfg = self._shlink_config()
+        mock_resp = MagicMock()
+        mock_resp.json.return_value = {"shortUrl": "https://short.example/abc123"}
+        session = MagicMock()
+        session.post.return_value = mock_resp
+
+        shorten_url_sync("https://example.com/long/path", config=cfg, session=session)
+
+        call = session.post.call_args
+        assert call[0][0] == "https://short.example/rest/v3/short-urls"
+        assert call.kwargs["headers"]["X-Api-Key"] == "test-api-key"
+        assert call.kwargs["headers"]["Content-Type"] == "application/json"
+        payload = json.loads(call.kwargs["data"])
+        assert payload["longUrl"] == "https://example.com/long/path"
+        assert payload["findIfExists"] is True
+
+    def test_falls_back_to_short_url_slug(self):
+        cfg = self._shlink_config()
+        mock_resp = MagicMock()
+        mock_resp.json.return_value = {"shortUrlSlug": "abc123"}
+        session = MagicMock()
+        session.post.return_value = mock_resp
+
+        out = shorten_url_sync("http://a.com", config=cfg, session=session)
+        assert out == "abc123"
+
+    def test_missing_short_url_in_response_returns_empty(self):
+        cfg = self._shlink_config()
+        mock_resp = MagicMock()
+        mock_resp.json.return_value = {"unexpected": "shape"}
+        session = MagicMock()
+        session.post.return_value = mock_resp
+
+        assert shorten_url_sync("http://a.com", config=cfg, session=session) == ""
+
+    def test_missing_api_key_skips_the_request(self):
+        """Regression: shlink genuinely needs an API key, unlike v.gd/is.gd, so it
+        must not attempt the call (and must not crash) when one isn't configured."""
+        cfg = self._shlink_config(short_url_website_api_key="")
+        session = MagicMock()
+
+        out = shorten_url_sync("http://a.com", config=cfg, session=session)
+
+        assert out == ""
+        session.post.assert_not_called()
+
+    def test_request_exception_returns_empty(self):
+        cfg = self._shlink_config()
+        session = MagicMock()
+        session.post.side_effect = requests.exceptions.ConnectionError("unreachable")
+
+        assert shorten_url_sync("http://a.com", config=cfg, session=session) == ""
+
+    def test_malformed_json_response_returns_empty(self):
+        cfg = self._shlink_config()
+        mock_resp = MagicMock()
+        mock_resp.json.side_effect = ValueError("not json")
+        session = MagicMock()
+        session.post.return_value = mock_resp
+
+        assert shorten_url_sync("http://a.com", config=cfg, session=session) == ""
+
+    @patch("modules.url_shortener.requests.post")
+    def test_no_session_uses_requests_post(self, mock_post):
+        cfg = self._shlink_config()
+        mock_resp = MagicMock()
+        mock_resp.json.return_value = {"shortUrl": "https://short.example/xyz"}
+        mock_post.return_value = mock_resp
+
+        out = shorten_url_sync("http://a.com", config=cfg, session=None)
+        assert out == "https://short.example/xyz"
+        mock_post.assert_called_once()
+
+
 @pytest.mark.asyncio
 async def test_shorten_url_async():
     from modules.url_shortener import shorten_url
@@ -196,3 +340,21 @@ async def test_shorten_url_async():
 
     out = await shorten_url("http://d.com", config=cfg, session=session)
     assert out == "https://v.gd/async1"
+
+
+@pytest.mark.asyncio
+async def test_shorten_url_async_shlink():
+    from modules.url_shortener import shorten_url
+
+    cfg = _minimal_config(
+        short_url_website_service="shlink",
+        short_url_website="https://short.example",
+        short_url_website_api_key="test-api-key",
+    )
+    mock_resp = MagicMock()
+    mock_resp.json.return_value = {"shortUrl": "https://short.example/async1"}
+    session = MagicMock()
+    session.post.return_value = mock_resp
+
+    out = await shorten_url("http://d.com", config=cfg, session=session)
+    assert out == "https://short.example/async1"