diff --git a/unbox.py b/unbox.py
index 93dd0aa..5ed2836 100644
--- a/unbox.py
+++ b/unbox.py
@@ -9,6 +9,10 @@ import urllib.request
 
 BASE_URL = os.environ.get("UNBOX_API_BASE", "https://api.unbox.tf")
 API_KEY_FILE = ".api_key"
+DEFAULT_HEADERS = {
+    "Accept": "application/json",
+    "User-Agent": "unbox.py/1.0 (+https://github.com/lexzach/unbox.py)",
+}
 
 
 def load_api_key():
@@ -29,7 +33,10 @@ def get_json(path, params=None, headers=None):
     url = f"{BASE_URL}{path}"
     if query:
         url = f"{url}?{query}"
-    req = urllib.request.Request(url, headers=headers or {})
+    req_headers = dict(DEFAULT_HEADERS)
+    if headers:
+        req_headers.update(headers)
+    req = urllib.request.Request(url, headers=req_headers)
     with urllib.request.urlopen(req) as resp:
         return json.load(resp)
 
@@ -39,11 +46,22 @@ def post_json(path, params=None, headers=None):
     url = f"{BASE_URL}{path}"
     if query:
         url = f"{url}?{query}"
-    req = urllib.request.Request(url, method="POST", headers=headers or {})
+    req_headers = dict(DEFAULT_HEADERS)
+    if headers:
+        req_headers.update(headers)
+    req = urllib.request.Request(url, method="POST", headers=req_headers)
     with urllib.request.urlopen(req) as resp:
         return json.load(resp)
 
 
+def http_error_details(e):
+    try:
+        body = e.read().decode("utf-8", "replace").strip()
+    except Exception:
+        body = ""
+    return body
+
+
 def main():
     use_alt = "--key" in sys.argv[1:]
     crate_ref_id = 2 if use_alt else 1
@@ -55,6 +73,9 @@ def main():
         crates_resp = get_json("/user/crates", headers=headers)
     except urllib.error.HTTPError as e:
         print(f"Failed to fetch crates: {e.code} {e.reason}")
+        body = http_error_details(e)
+        if body:
+            print(body)
         return 1
     except urllib.error.URLError as e:
         print(f"Failed to fetch crates: {e.reason}")
@@ -77,9 +98,16 @@ def main():
         return 1
 
     try:
-        unbox_resp = post_json("/unbox", params={"crate_id": crate_id}, headers=headers)
+        unbox_resp = post_json(
+            "/unbox",
+            params={"crate_id": crate_id},
+            headers=headers,
+        )
     except urllib.error.HTTPError as e:
         print(f"Failed to unbox: {e.code} {e.reason}")
+        body = http_error_details(e)
+        if body:
+            print(body)
         return 1
     except urllib.error.URLError as e:
         print(f"Failed to unbox: {e.reason}")