diff --git a/compat/dsn.py b/compat/dsn.py
index 561ebaa..bc7a297 100644
--- a/compat/dsn.py
+++ b/compat/dsn.py
@@ -58,3 +58,18 @@ def get_header_value(sentry_dsn):
 def get_sentry_key(sentry_dsn):
     parts = urllib.parse.urlsplit(sentry_dsn)
     return parts.username
+
+
+def validate_sentry_dsn(sentry_dsn):
+    parts = urllib.parse.urlsplit(sentry_dsn)
+
+    if not parts.scheme or not parts.hostname or not parts.username:
+        raise ValueError("Invalid Sentry DSN format. It must contain a scheme, hostname, and public_key.")
+
+    if parts.scheme not in ("http", "https"):
+        raise ValueError("Invalid Sentry DSN scheme. It must be 'http' or 'https'.")
+
+    if (not parts.path) or ("/" not in parts.path) or (not parts.path.rsplit("/", 1)[1]):
+        raise ValueError("Invalid DSN: path must include '/<project_id>'")
+
+    return True
diff --git a/ingest/exceptions.py b/ingest/exceptions.py
new file mode 100644
index 0000000..831cca9
--- /dev/null
+++ b/ingest/exceptions.py
@@ -0,0 +1,2 @@
+class ParseError(Exception):
+    pass
diff --git a/ingest/header_validators.py b/ingest/header_validators.py
new file mode 100644
index 0000000..c82caaa
--- /dev/null
+++ b/ingest/header_validators.py
@@ -0,0 +1,101 @@
+import re
+from datetime import datetime
+
+from compat.dsn import validate_sentry_dsn
+from .exceptions import ParseError
+
+
+# Based on the documentation here:
+#
+#   https://develop.sentry.dev/sdk/data-model/envelopes/
+#   https://develop.sentry.dev/sdk/data-model/envelope-items/
+#
+# From the docs, we deduced validation for
+#
+# * envelope headers -> all of them
+# * item headers -> only those that are relevant for "event" items
+
+
+_RFC3339_Z = re.compile(r"^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d+)?Z$")
+_UUID32 = re.compile(r"^[0-9a-fA-F]{32}$")
+_UUID36 = re.compile(r"^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$")
+
+
+def validate_dsn(v):
+    try:
+        validate_sentry_dsn(v)
+    except ValueError as e:
+        raise ParseError(f'Envelope header "dsn" invalid: {e}')
+
+
+def validate_sdk(v):
+    if not isinstance(v, dict):
+        raise ParseError('Envelope header "sdk" must be an object')
+
+
+def validate_sent_at(v):
+    if not isinstance(v, str) or not _RFC3339_Z.match(v):
+        raise ParseError(f'Envelope header "sent_at" must be an RFC3339 UTC timestamp ending in Z: {v}')
+
+    try:
+        datetime.strptime(v, "%Y-%m-%dT%H:%M:%SZ")
+    except ValueError:
+        datetime.fromisoformat(v.replace("Z", "+00:00"))
+
+
+def validate_event_id(v):
+    if not isinstance(v, str) or not (_UUID32.match(v) or _UUID36.match(v)):
+        raise ParseError(f'Envelope header "event_id" must be a valid UUID string: {v}')
+
+
+envelope_validators = {
+    "dsn": validate_dsn,
+    "sdk": validate_sdk,
+    "sent_at": validate_sent_at,
+    "event_id": validate_event_id,
+}
+
+
+def validate_envelope_headers(headers):
+    for key, val in headers.items():
+        if key in envelope_validators:
+            envelope_validators[key](val)
+
+
+ALLOWED_TYPES = {
+    "event", "transaction", "attachment", "session", "sessions", "feedback", "user_report", "client_report",
+    "replay_event", "replay_recording", "profile", "profile_chunk", "check_in", "log", "otel_log"
+}
+
+
+def validate_type(v):
+    return
+    # alternatively (1):
+    # if v not in _allowed_types:
+    # Sentry's protocol might add new item types in the future; we don't want to raise an error for those.
+    # logger.warning(f'Item header "type" is not recognized: {v}.'
+    #
+    # alternatively (2):
+    # raise ParseError(f'Item header "type" must be one of {_allowed_types}, got: {v}')
+
+
+def _validate_length(v):
+    if not isinstance(v, int) or v < 0:
+        raise ParseError(f'Item header "length" must be a non-negative integer, got: {v}')
+
+
+item_validators = {
+    "type": validate_type,
+    "length": _validate_length,
+}
+
+
+def validate_item_headers(headers):
+    if headers.get("type") != "event":
+        # Only validate item headers for events. Reason: it's the only type of event that we actually process; rather
+        # than trying to keep the validation in sync with for a part of the protocol that we don't use, we skip it.
+        return
+
+    for key, val in headers.items():
+        if key in item_validators:
+            item_validators[key](val)
diff --git a/ingest/parsers.py b/ingest/parsers.py
index 3da7b29..f60f8bc 100644
--- a/ingest/parsers.py
+++ b/ingest/parsers.py
@@ -3,9 +3,8 @@ import io
 
 from bugsink.streams import MaxDataWriter
 
-
-class ParseError(Exception):
-    pass
+from .exceptions import ParseError
+from .header_validators import validate_envelope_headers, validate_item_headers
 
 
 class NewlineFinder:
@@ -150,6 +149,7 @@ class StreamingEnvelopeParser:
         if self.envelope_headers is None:
             # see test_eof_after_envelope_headers for why we don't error on EOF-after-header here
             self.envelope_headers = self._parse_headers(empty_is_error=True, eof_after_header_is_error=False)
+            validate_envelope_headers(self.envelope_headers)
 
         return self.envelope_headers
 
@@ -161,10 +161,13 @@ class StreamingEnvelopeParser:
 
         while not self.at_eof:
             item_headers = self._parse_headers(empty_is_error=False, eof_after_header_is_error=True)
+
             if item_headers is None:
                 self.at_eof = True
                 break
 
+            validate_item_headers(item_headers)
+
             if "length" in item_headers:
                 length = item_headers["length"]
                 finder = LengthFinder(length, error_for_eof="EOF while reading item with explicitly specified length")