diff --git a/src/specify_cli/_github_http.py b/src/specify_cli/_github_http.py
index ee68a8325c..ffa804dbb7 100644
--- a/src/specify_cli/_github_http.py
+++ b/src/specify_cli/_github_http.py
@@ -8,8 +8,8 @@
 
 import os
 import urllib.request
-from urllib.parse import urlparse
 from typing import Dict
+from urllib.parse import urlparse
 
 # GitHub-owned hostnames that should receive the Authorization header.
 # Includes codeload.github.com because GitHub archive URL downloads
@@ -30,12 +30,25 @@ def build_github_request(url: str) -> urllib.request.Request:
     ``Authorization: Bearer <value>`` header when the target hostname is one
     of the known GitHub-owned domains. Non-GitHub URLs are returned as plain
     requests so credentials are never leaked to third-party hosts.
+
+    Raises:
+        ValueError: If ``url`` is empty or whitespace-only.
+        ValueError: If ``url`` does not use the ``http`` or ``https`` scheme.
+        ValueError: If ``url`` does not include a hostname.
     """
     headers: Dict[str, str] = {}
+    url = url.strip()
+    if not url:
+        raise ValueError("url must not be empty")
+    parsed = urlparse(url)
+    if parsed.scheme not in {"http", "https"}:
+        raise ValueError(f"url must start with http:// or https://, got: {url!r}")
+    if not parsed.hostname:
+        raise ValueError(f"url must include a hostname, got: {url!r}")
     github_token = (os.environ.get("GITHUB_TOKEN") or "").strip()
     gh_token = (os.environ.get("GH_TOKEN") or "").strip()
     token = github_token or gh_token or None
-    hostname = (urlparse(url).hostname or "").lower()
+    hostname = parsed.hostname.lower()
     if token and hostname in GITHUB_HOSTS:
         headers["Authorization"] = f"Bearer {token}"
     return urllib.request.Request(url, headers=headers)
diff --git a/tests/test_github_http.py b/tests/test_github_http.py
new file mode 100644
index 0000000000..f414aeeb2b
--- /dev/null
+++ b/tests/test_github_http.py
@@ -0,0 +1,79 @@
+"""Tests for GitHub-authenticated HTTP request helpers."""
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from specify_cli._github_http import (
+    build_github_request,
+)
+
+
+class TestBuildGitHubRequest:
+    """Tests for build_github_request() URL validation and auth handling."""
+
+    # --- URL Validation Tests ---
+
+    def test_empty_url_raises_value_error(self):
+        """build_github_request() must reject an empty string URL."""
+        with pytest.raises(ValueError, match="url must not be empty"):
+            build_github_request("")
+
+    def test_whitespace_url_raises_value_error(self):
+        """build_github_request() must reject a whitespace-only URL."""
+        with pytest.raises(ValueError, match="url must not be empty"):
+            build_github_request("   ")
+
+    def test_non_http_url_raises_value_error(self):
+        """build_github_request() must reject URLs without http/https scheme."""
+        with pytest.raises(ValueError, match="url must start with http"):
+            build_github_request("not-a-url")
+
+    def test_ftp_url_raises_value_error(self):
+        """build_github_request() must reject ftp:// URLs."""
+        with pytest.raises(ValueError, match="url must start with http"):
+            build_github_request("ftp://github.com/file.zip")
+
+    # --- Valid URL Tests ---
+
+    def test_valid_https_url_returns_request(self):
+        """build_github_request() must return a Request for a valid https URL."""
+        req = build_github_request("https://github.com/github/spec-kit")
+        assert req.full_url == "https://github.com/github/spec-kit"
+
+    def test_valid_http_url_returns_request(self):
+        """build_github_request() must accept http:// URLs."""
+        req = build_github_request("http://example.com/file")
+        assert req.full_url == "http://example.com/file"
+
+    # --- Auth Header Tests ---
+
+    def test_github_token_added_for_github_host(self):
+        """Authorization header is set when GITHUB_TOKEN is present."""
+        with patch.dict(os.environ, {"GITHUB_TOKEN": "test-token", "GH_TOKEN": ""}):
+            req = build_github_request("https://github.com/github/spec-kit")
+        assert req.get_header("Authorization") == "Bearer test-token"
+
+    def test_gh_token_used_as_fallback(self):
+        """GH_TOKEN is used when GITHUB_TOKEN is absent."""
+        with patch.dict(os.environ, {"GITHUB_TOKEN": "", "GH_TOKEN": "fallback-token"}):
+            req = build_github_request("https://github.com/github/spec-kit")
+        assert req.get_header("Authorization") == "Bearer fallback-token"
+
+    def test_no_auth_header_for_non_github_host(self):
+        """Authorization header must NOT be set for non-GitHub URLs."""
+        with patch.dict(os.environ, {"GITHUB_TOKEN": "test-token"}):
+            req = build_github_request("https://example.com/file")
+        assert req.get_header("Authorization") is None
+
+    def test_no_auth_header_when_no_token(self):
+        """No Authorization header when no token is set in environment."""
+        with patch.dict(os.environ, {}, clear=True):
+            req = build_github_request("https://github.com/github/spec-kit")
+        assert req.get_header("Authorization") is None
+
+    def test_missing_hostname_raises_value_error(self):
+        """build_github_request() must reject URLs with valid scheme but no hostname."""
+        with pytest.raises(ValueError, match="url must include a hostname"):
+            build_github_request("http://")
\ No newline at end of file