diff --git a/samples/sample_tap_csv/client.py b/samples/sample_tap_csv/client.py
index b0ff13923..c5a40bfe2 100644
--- a/samples/sample_tap_csv/client.py
+++ b/samples/sample_tap_csv/client.py
@@ -4,14 +4,22 @@
 import typing as t
 
 from singer_sdk.contrib.filesystem import FileStream
+from singer_sdk.contrib.filesystem.stream import SDC_META_FILEPATH
 
 if t.TYPE_CHECKING:
     from singer_sdk.helpers.types import Record
 
 
+SDC_META_LINE_NUMBER = "_sdc_line_number"
+
+
 class CSVStream(FileStream):
     """CSV stream class."""
 
+    @property
+    def primary_keys(self) -> t.Sequence[str]:
+        return (SDC_META_FILEPATH, SDC_META_LINE_NUMBER)
+
     def get_schema(self, path: str) -> dict[str, t.Any]:
         with self.filesystem.open(path, mode="r") as file:
             reader = csv.DictReader(
@@ -22,10 +30,12 @@ def get_schema(self, path: str) -> dict[str, t.Any]:
                 doublequote=self.config["doublequote"],
                 lineterminator=self.config["lineterminator"],
             )
-            return {
+            schema = {
                 "type": "object",
                 "properties": {key: {"type": "string"} for key in reader.fieldnames},
             }
+            schema["properties"][SDC_META_LINE_NUMBER] = {"type": "integer"}
+            return schema
 
     def read_file(self, path: str) -> t.Iterable[Record]:
         with self.filesystem.open(path, mode="r") as file:
@@ -37,4 +47,6 @@ def read_file(self, path: str) -> t.Iterable[Record]:
                 doublequote=self.config["doublequote"],
                 lineterminator=self.config["lineterminator"],
             )
-            yield from reader
+            for record in reader:
+                record[SDC_META_LINE_NUMBER] = reader.line_num
+                yield record
diff --git a/singer_sdk/contrib/filesystem/stream.py b/singer_sdk/contrib/filesystem/stream.py
index a1b71da16..4c1b285de 100644
--- a/singer_sdk/contrib/filesystem/stream.py
+++ b/singer_sdk/contrib/filesystem/stream.py
@@ -132,10 +132,10 @@ def get_records(
             record[SDC_META_FILEPATH] = path
             yield record
 
-    @abc.abstractmethod
-    def read_file(self, path: str) -> t.Iterable[Record]:
-        """Return a generator of records from the file."""
-
     @abc.abstractmethod
     def get_schema(self, path: str) -> dict[str, t.Any]:
         """Return the schema for the file."""
+
+    @abc.abstractmethod
+    def read_file(self, path: str) -> t.Iterable[Record]:
+        """Return a generator of records from the file."""
diff --git a/singer_sdk/contrib/filesystem/tap.py b/singer_sdk/contrib/filesystem/tap.py
index 6e3b07f47..f2fd7c352 100644
--- a/singer_sdk/contrib/filesystem/tap.py
+++ b/singer_sdk/contrib/filesystem/tap.py
@@ -89,8 +89,16 @@ class FolderTap(Tap, t.Generic[_T]):
     """Singer tap for files in a directory."""
 
     valid_extensions: tuple[str, ...]
+    """Valid file extensions for this tap.
+
+    Files with extensions not in this list will be ignored.
+    """
 
     default_stream_class: type[_T]
+    """The default stream class to use for this tap.
+
+    This should be a subclass of `FileStream`.
+    """
 
     config_jsonschema: t.ClassVar[dict] = {"properties": {}}