diff --git a/src/collect_data.py b/src/collect_data.py
index dc61fe0..445202d 100644
--- a/src/collect_data.py
+++ b/src/collect_data.py
@@ -23,6 +23,7 @@
 
 # yuck - but simplest way to avoid changing directory structure
 sys.path.insert(0, "src")
+from ts_afdist import ts_afdist
 from zarr_afdist import zarr_afdist, classify_genotypes_subset_filter, zarr_decode
 
 
@@ -216,6 +217,30 @@ def run_ts_afdist(path, *, debug=False):
     return time_cli_command(cmd, debug)
 
 
+def py_ts_afdist_worker(path, debug, conn):
+    before = time.time()
+    df = ts_afdist(path / "call_genotype")
+    wall_time = time.time() - before
+    cpu_times = psutil.Process().cpu_times()
+    conn.send(f"{wall_time} {cpu_times.user} {cpu_times.system}")
+
+    if debug:
+        print(df)
+
+
+def run_py_ts_afdist(path, *, debug: bool = False):
+    conn1, conn2 = multiprocessing.Pipe()
+    p = multiprocessing.Process(target=py_ts_afdist_worker, args=(path, debug, conn2))
+    p.start()
+    value = conn1.recv()
+    wall_time, user_time, sys_time = map(float, value.split())
+    p.join()
+    if p.exitcode != 0:
+        raise ValueError()
+    p.close()
+    return ProcessTimeResult(wall_time, sys_time, user_time)
+
+
 def run_savvy_decode(path, *, debug=False):
     cmd = (
         "/usr/bin/time -f'%S %U' "
@@ -438,6 +463,13 @@ def zarr_version():
         None,
         None,
     ),
+    Tool(
+        "ts_py",
+        ".zarr",
+        run_py_ts_afdist,
+        None,
+        None,
+    ),
 ]
 
 
diff --git a/src/ts_afdist.py b/src/ts_afdist.py
new file mode 100644
index 0000000..41b26f5
--- /dev/null
+++ b/src/ts_afdist.py
@@ -0,0 +1,55 @@
+import numpy as np
+import pandas as pd
+import tensorstore as ts
+
+def ts_afdist(path):
+    path = str(path)
+    store = ts.open({
+            "driver": "zarr",
+            "kvstore": {
+                "driver": "file",
+                "path": path,
+            },
+    }, write=False).result()
+    variant_count = store.shape[0]
+    sample_count = store.shape[1]
+    chunk_shape = store.chunk_layout.read_chunk.shape
+    variant_chunk_size = chunk_shape[0]
+    sample_chunk_size = chunk_shape[1]
+    bin_counts = np.zeros((11,), dtype=int)
+
+    for variant_chunk_start in range(0, variant_count, variant_chunk_size):
+        variant_chunk_end = min(variant_count, variant_chunk_start + variant_chunk_size)
+        variant_chunk_len = variant_chunk_end - variant_chunk_start
+        ref_counts = np.zeros((variant_chunk_len,), dtype=int)
+        het_counts = np.zeros((variant_chunk_len,), dtype=int)
+        hom_alt_counts = np.zeros((variant_chunk_len,), dtype=int)
+
+        for sample_chunk_start in range(0, sample_count, sample_chunk_size):
+            sample_chunk_end = min(sample_count, sample_chunk_start + sample_chunk_size)
+
+            chunk = store[variant_chunk_start:variant_chunk_end, sample_chunk_start:sample_chunk_end].read().result()
+            a = chunk[:, :, 0]
+            b = chunk[:, :, 1]
+
+            chunk_ref_counts = ((a == 0).astype(int) + (b == 0).astype(int)).sum(axis=1)
+            chunk_het_counts = (a != b).sum(axis=1)
+            chunk_hom_alt_counts = np.logical_and(a == b, a > 0).sum(axis=1)
+
+            np.add(ref_counts, chunk_ref_counts, out=ref_counts)
+            np.add(het_counts, chunk_het_counts, out=het_counts)
+            np.add(hom_alt_counts, chunk_hom_alt_counts, out=hom_alt_counts)
+
+        alt_count = 2 * sample_count - ref_counts
+        alt_freq = alt_count / (2 * sample_count)
+        het_ref_freq = 2 * alt_freq * (1 - alt_freq)
+        hom_alt_freq = alt_freq * alt_freq
+
+        bins = np.linspace(0, 1.0, len(bin_counts))
+        bins[-1] += 0.0125
+        a = np.bincount(np.digitize(het_ref_freq, bins), weights=het_counts, minlength=len(bins)).astype(int)
+        b = np.bincount(np.digitize(hom_alt_freq, bins), weights=hom_alt_counts, minlength=len(bins)).astype(int)
+        np.add(bin_counts, a, out=bin_counts)
+        np.add(bin_counts, b, out=bin_counts)
+
+    return pd.DataFrame({"start": bins[:-1], "stop": bins[1:], "prob dist": bin_counts[1:]})