diff --git a/api/src/damnit_api/base/__init__.py b/api/src/damnit_api/base/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/api/src/damnit_api/base/exceptions.py b/api/src/damnit_api/base/exceptions.py
new file mode 100644
index 0000000..75f9185
--- /dev/null
+++ b/api/src/damnit_api/base/exceptions.py
@@ -0,0 +1,15 @@
+from pathlib import Path
+
+from fastapi import HTTPException
+
+
+class DWAError(Exception): ...
+
+
+class DWAHTTPError(DWAError, HTTPException): ...
+
+
+class InvalidProposalPathError(DWAError):
+    def __init__(self, path: Path):
+        self.path = path
+        super().__init__(f"Invalid proposal path: {path}")
diff --git a/api/src/damnit_api/base/models.py b/api/src/damnit_api/base/models.py
new file mode 100644
index 0000000..1d71e4c
--- /dev/null
+++ b/api/src/damnit_api/base/models.py
@@ -0,0 +1,53 @@
+import re
+from pathlib import Path
+from typing import NewType, Self
+
+from pydantic import BaseModel
+
+from .exceptions import InvalidProposalPathError
+
+ProposalNumber = NewType("ProposalNumber", int)
+
+_RE_PNFS_SUB = re.compile(
+    r"/pnfs/xfel\.eu/exfel/archive/XFEL/(?:proc|raw)"
+    r"/(?P<inst>[^/]+)/(?P<cycle>[^/]+)/p(?P<prop>[^/]+)"
+)
+
+_RE_GPFS = re.compile(
+    r"/gpfs/exfel/exp/(?P<inst>[^/]+)/(?P<cycle>[^/]+)/p(?P<prop>[^/]+)"
+)
+
+_RE_GPFS_SUB = re.compile(
+    r"/gpfs/exfel/(?:u/scratch|u/usr|d/proc|d/raw)"
+    r"/(?P<inst>[^/]+)/(?P<cycle>[^/]+)/p(?P<prop>[^/]+)"
+)
+
+_RE_LIST = [_RE_PNFS_SUB, _RE_GPFS, _RE_GPFS_SUB]
+
+
+class ProposalPath(BaseModel):
+    instrument: str
+    cycle: int
+    number: ProposalNumber
+
+    @property
+    def dirname(self) -> str:
+        return f"p{self.number:06d}"
+
+    @property
+    def path(self) -> Path:
+        return Path(f"/gpfs/exfel/exp/{self.instrument}/{self.cycle}/{self.dirname}")
+
+    @classmethod
+    def from_path(cls, path: Path) -> Self:
+        match = [m.match(str(path)) for m in _RE_LIST]
+        match = [m for m in match if m]
+
+        if not match:
+            raise InvalidProposalPathError(path)
+
+        group = match[0].groupdict()
+
+        inst, cycle, no = group["inst"], group["cycle"], int(group["prop"])
+
+        return cls(instrument=inst, cycle=int(cycle), number=ProposalNumber(no))