diff --git a/custom_components/openai_compatible/config_flow.py b/custom_components/openai_compatible/config_flow.py
index 5df3fcc..2c4da64 100644
--- a/custom_components/openai_compatible/config_flow.py
+++ b/custom_components/openai_compatible/config_flow.py
@@ -103,6 +103,7 @@ from .const import (
     UNSUPPORTED_PRIORITY_SERVICE_TIERS_MODELS,
     UNSUPPORTED_WEB_SEARCH_MODELS,
 )
+from .url_util import InvalidBaseURL, normalize_base_url
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -119,6 +120,7 @@ async def validate_input(hass: HomeAssistant, data: dict[str, Any]) -> None:
 
     Data has the keys from STEP_USER_DATA_SCHEMA with values provided by the user.
     """
+    data[CONF_BASE_URL] = normalize_base_url(data[CONF_BASE_URL])
     client = openai.AsyncOpenAI(
         api_key=data[CONF_API_KEY],
         base_url=data[CONF_BASE_URL],
@@ -145,6 +147,8 @@ class OpenAIConfigFlow(ConfigFlow, domain=DOMAIN):
             self._async_abort_entries_match(user_input)
             try:
                 await validate_input(self.hass, user_input)
+            except InvalidBaseURL:
+                errors["base"] = "invalid_base_url"
             except openai.APIConnectionError:
                 errors["base"] = "cannot_connect"
             except openai.AuthenticationError:
diff --git a/custom_components/openai_compatible/strings.json b/custom_components/openai_compatible/strings.json
index ab30ee9..f4bac57 100644
--- a/custom_components/openai_compatible/strings.json
+++ b/custom_components/openai_compatible/strings.json
@@ -7,6 +7,7 @@
     "error": {
       "cannot_connect": "[%key:common::config_flow::error::cannot_connect%]",
       "invalid_auth": "[%key:common::config_flow::error::invalid_auth%]",
+      "invalid_base_url": "That does not look like a valid http(s) URL.",
       "unknown": "[%key:common::config_flow::error::unknown%]"
     },
     "step": {
diff --git a/custom_components/openai_compatible/url_util.py b/custom_components/openai_compatible/url_util.py
new file mode 100644
index 0000000..7ddd7c9
--- /dev/null
+++ b/custom_components/openai_compatible/url_util.py
@@ -0,0 +1,42 @@
+"""Base-URL normalization and safe logging.
+
+This module is intentionally separate from the vendored upstream files so that
+re-syncing with home-assistant/core never conflicts with it.
+"""
+
+from __future__ import annotations
+
+from urllib.parse import urlparse, urlunparse
+
+ALLOWED_SCHEMES = frozenset({"http", "https"})
+
+
+class InvalidBaseURL(ValueError):
+    """Raised when a base URL is unusable."""
+
+
+def normalize_base_url(url: str) -> str:
+    """Strip whitespace and trailing slashes, and validate the scheme."""
+    cleaned = (url or "").strip()
+    if not cleaned:
+        raise InvalidBaseURL("base URL is empty")
+
+    parsed = urlparse(cleaned)
+    if parsed.scheme not in ALLOWED_SCHEMES:
+        raise InvalidBaseURL(f"unsupported scheme: {parsed.scheme or '(none)'}")
+    if not parsed.netloc:
+        raise InvalidBaseURL("base URL has no host")
+
+    return urlunparse(parsed._replace(path=parsed.path.rstrip("/")))
+
+
+def sanitize_url_for_logging(url: str) -> str:
+    """Return the URL with any embedded credentials replaced by ***."""
+    parsed = urlparse(url)
+    if not parsed.username and not parsed.password:
+        return url
+
+    host = parsed.hostname or ""
+    if parsed.port:
+        host = f"{host}:{parsed.port}"
+    return urlunparse(parsed._replace(netloc=f"***@{host}"))
diff --git a/tests/test_url_util.py b/tests/test_url_util.py
new file mode 100644
index 0000000..caba024
--- /dev/null
+++ b/tests/test_url_util.py
@@ -0,0 +1,39 @@
+"""URL hygiene: normalize input, never log credentials."""
+
+import pytest
+
+from custom_components.openai_compatible.url_util import (
+    InvalidBaseURL,
+    normalize_base_url,
+    sanitize_url_for_logging,
+)
+
+
+@pytest.mark.parametrize(
+    ("raw", "expected"),
+    [
+        ("http://192.0.2.10:4000/v1", "http://192.0.2.10:4000/v1"),
+        ("http://192.0.2.10:4000/v1/", "http://192.0.2.10:4000/v1"),
+        ("  https://api.openai.com/v1  ", "https://api.openai.com/v1"),
+        ("http://host:4000/v1///", "http://host:4000/v1"),
+    ],
+)
+def test_normalize(raw, expected):
+    assert normalize_base_url(raw) == expected
+
+
+@pytest.mark.parametrize("raw", ["ftp://host/v1", "not-a-url", "", "   "])
+def test_normalize_rejects(raw):
+    with pytest.raises(InvalidBaseURL):
+        normalize_base_url(raw)
+
+
+def test_sanitize_strips_credentials():
+    assert (
+        sanitize_url_for_logging("https://user:secret@host:4000/v1")
+        == "https://***@host:4000/v1"
+    )
+
+
+def test_sanitize_leaves_clean_urls_alone():
+    assert sanitize_url_for_logging("http://host:4000/v1") == "http://host:4000/v1"