diff --git a/sparse_autoencoder/paths.py b/sparse_autoencoder/paths.py
index 9619a11..0759f1c 100644
--- a/sparse_autoencoder/paths.py
+++ b/sparse_autoencoder/paths.py
@@ -1,3 +1,9 @@
+BASE_URL = "az://openaipublic/sparse-autoencoder/gpt2-small"
+VALID_LOCATIONS_V1_V4 = ["mlp_post_act", "resid_delta_mlp"]
+VALID_LOCATIONS_V5 = ["resid_delta_attn", "resid_delta_mlp", "resid_post_attn", "resid_post_mlp"]
+
+def generate_url(location: str, layer_index: int, version: str) -> str:
+    return f"{BASE_URL}/{location}_{version}/autoencoders/{layer_index}.pt"
 
 def v1(location, layer_index):
     """
@@ -10,18 +16,18 @@ def v1(location, layer_index):
     - NeuronRecord files:
         `az://openaipublic/sparse-autoencoder/gpt2-small/{location}/collated_activations/{layer_index}/{latent_index}.json`
     """
-    assert location in ["mlp_post_act", "resid_delta_mlp"]
-    assert layer_index in range(12)
-    return f"az://openaipublic/sparse-autoencoder/gpt2-small/{location}/autoencoders/{layer_index}.pt"
+    assert location in VALID_LOCATIONS_V1_V4, f"Invalid location: {location}"
+    assert layer_index in range(12), f"Invalid layer_index: {layer_index}"
+    return f"{BASE_URL}/{location}/autoencoders/{layer_index}.pt"
 
 def v4(location, layer_index):
     """
     Details:
     same as v1
     """
-    assert location in ["mlp_post_act", "resid_delta_mlp"]
-    assert layer_index in range(12)
-    return f"az://openaipublic/sparse-autoencoder/gpt2-small/{location}_v4/autoencoders/{layer_index}.pt"
+    assert location in VALID_LOCATIONS_V1_V4, f"Invalid location: {location}"
+    assert layer_index in range(12), f"Invalid layer_index: {layer_index}"
+    return generate_url(location, layer_index, "v4")
 
 def v5_32k(location, layer_index):
     """
@@ -32,10 +38,10 @@ def v5_32k(location, layer_index):
     - L1 regularization strength: n/a
     - Layer normed inputs: true
     """
-    assert location in ["resid_delta_attn", "resid_delta_mlp", "resid_post_attn", "resid_post_mlp"]
-    assert layer_index in range(12)
+    assert location in VALID_LOCATIONS_V5, f"Invalid location: {location}"
+    assert layer_index in range(12), f"Invalid layer_index: {layer_index}"
     # note: it's actually 2**15 and 2**17 ~= 131k
-    return f"az://openaipublic/sparse-autoencoder/gpt2-small/{location}_v5_32k/autoencoders/{layer_index}.pt"
+    return generate_url(location, layer_index, "v5_32k")
 
 def v5_128k(location, layer_index):
     """
@@ -46,10 +52,10 @@ def v5_128k(location, layer_index):
     - L1 regularization strength: n/a
     - Layer normed inputs: true
     """
-    assert location in ["resid_delta_attn", "resid_delta_mlp", "resid_post_attn", "resid_post_mlp"]
-    assert layer_index in range(12)
+    assert location in VALID_LOCATIONS_V5, f"Invalid location: {location}"
+    assert layer_index in range(12), f"Invalid layer_index: {layer_index}"
     # note: it's actually 2**15 and 2**17 ~= 131k
-    return f"az://openaipublic/sparse-autoencoder/gpt2-small/{location}_v5_128k/autoencoders/{layer_index}.pt"
+    return generate_url(location, layer_index, "v5_128k")
 
 # NOTE: we have larger autoencoders (up to 8M, with varying n and k) trained on layer 8 resid_post_mlp
 # we may release them in the future