diff --git a/README.md b/README.md
index 59a3efc..6c4416b 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,13 @@
-**Hello world!!!**
+# PD V3 Post-Processing
+
+- **Inputs:** Raw/isotonic PD outputs and model T weight from the processing block.
+- **Outputs:** Final weighted PD and assigned grade.
+- **Artifacts:** `grade_cutoffs.csv` generated from the Weighted Grades Cutoff workbook tab.
+- **Tests:** `python -m unittest sequence-3.pd_v3_post_processing.test_block`.
+- **Signature:** Sequence-3 convention: `__main__` must keep an explicit typed parameter list covering every input (int/float/str) and build the record from those args before weighting/grades; keep aligned with the block schemas.
+- **UAT tolerance:** Downstream sequence-3 UAT scripts treat post-processing mismatches within `1e-4` as equivalent to expected values.
+- **PD inputs:** `pd_a`, `pd_b`, and `pd_t` must be provided as non-null numbers (per schema); post-processing raises if any are missing/null.
+
+## Schema notes
+
+- The request and response schemas for post-processing are treated as immutable contracts. They already describe flat scalar fields (plus the array `pd_scores`), so keep them as-is and never refactor them into dict-of-dicts/object-of-dicts—arrays of dicts remain acceptable.
diff --git a/__init__.py b/__init__.py
new file mode 100644
index 0000000..d3d26ed
--- /dev/null
+++ b/__init__.py
@@ -0,0 +1 @@
+__all__ = ["__main__"]
diff --git a/block.py b/block.py
index 3b227f9..199ebb6 100644
--- a/block.py
+++ b/block.py
@@ -1,21 +1,116 @@
-@flowx_block
-def example_function(request: dict) -> dict:
+from __future__ import annotations
 
-  # Processing logic here...
+import math
+from pathlib import Path
+from typing import Dict, List, Sequence, Tuple, TypedDict
 
-  return {
-    "meta_info": [
-      {
-        "name": "created_date",
-        "type": "string",
-        "value": "2024-11-05"
-      }
-    ],
-    "fields": [
-      {
-        "name": "",
-        "type": "",
-        "value": ""
-      }
-    ]
-  }
+import joblib
+
+
+MODELS_DIR = Path(__file__).parent
+GRADE_FILE = Path(__file__).parent / "grade_cutoffs.csv"
+
+_GRADE_TABLE: List[Tuple[str, float, float]] | None = None
+_ISOTONIC_MODELS: Dict[str, object] = {}
+ISOTONIC_FILES = {
+    "a": MODELS_DIR / "isotonic_model_A.joblib",
+    "b": MODELS_DIR / "isotonic_model_B.joblib",
+}
+
+
+class ScoreEntry(TypedDict):
+    name: str
+    value: float
+
+
+def _load_grade_table() -> None:
+    global _GRADE_TABLE
+    if _GRADE_TABLE is not None:
+        return
+
+    table: List[Tuple[str, float, float]] = []
+    with GRADE_FILE.open("r", encoding="utf-8") as handle:
+        next(handle)  # skip header
+        for line in handle:
+            grade, min_pd, max_pd = line.strip().split(",")
+            table.append((grade, float(min_pd), float(max_pd)))
+
+    table.sort(key=lambda row: row[1])
+    _GRADE_TABLE = table
+
+
+def _ensure_isotonic_models_loaded() -> None:
+    for key, path in ISOTONIC_FILES.items():
+        if key in _ISOTONIC_MODELS:
+            continue
+        _ISOTONIC_MODELS[key] = joblib.load(path)
+
+
+def _clamp_probability(value: float) -> float:
+    return min(1.0, max(0.0, float(value)))
+
+
+def _determine_grade(final_pd: float) -> str | None:
+    if final_pd is None or _GRADE_TABLE is None:
+        return None
+
+    for grade, min_pd, max_pd in _GRADE_TABLE:
+        if min_pd <= final_pd < max_pd:
+            return grade
+    # Allow equality with the top boundary to fall into the final grade.
+    last_grade, min_pd, max_pd = _GRADE_TABLE[-1]
+    if math.isclose(final_pd, max_pd):
+        return last_grade
+    return None
+
+
+def _apply_isotonic(model_key: str, raw_pd: float) -> float:
+    calibrator = _ISOTONIC_MODELS.get(model_key)
+    if calibrator is None:
+        return _clamp_probability(raw_pd)
+    calibrated = calibrator.predict([raw_pd])[0]
+    return _clamp_probability(calibrated)
+
+
+def __main__(
+    pd_a: float,
+    pd_b: float,
+    pd_t: float
+   
+) -> Dict[str, float | str]:
+    """
+    Inputs (request schema):
+    - pd_scores: ordered list of {"name": "pd_a"|"pd_b"|"pd_t", "value": <float>} entries
+    - pd_scores_pd_a / pd_scores_pd_b / pd_scores_pd_t: explicit, non-null PD inputs; must match pd_scores when provided
+
+    Outputs (response schema):
+    - pd_a: raw PD A clamped to [0,1]
+    - pd_b: raw PD B clamped to [0,1]
+    - pd_t: model T probability clamped to [0,1]
+    - pd_iso_a: isotonic-calibrated PD A
+    - pd_iso_b: isotonic-calibrated PD B
+    - final_pd: weighted final PD using pd_t as weight
+    - grade: assigned grade from the cutoff table
+    """
+
+    _load_grade_table()
+    _ensure_isotonic_models_loaded()
+
+
+    weight = _clamp_probability(pd_t)
+    pd_iso_a = _apply_isotonic("a", pd_a)
+    pd_iso_b = _apply_isotonic("b", pd_b)
+
+    final_pd = (pd_iso_a * weight) + (pd_iso_b * (1 - weight))
+
+    grade = _determine_grade(final_pd)
+
+    return {
+        "pd_a": _clamp_probability(pd_a),
+        "pd_b": _clamp_probability(pd_b),
+        "pd_t": weight,
+        "pd_iso_a": pd_iso_a,
+        "pd_iso_b": pd_iso_b,
+        "final_pd": final_pd,
+        "grade": grade if grade is not None else "",
+    }
diff --git a/grade_cutoffs.csv b/grade_cutoffs.csv
new file mode 100644
index 0000000..cfc4ae8
--- /dev/null
+++ b/grade_cutoffs.csv
@@ -0,0 +1,7 @@
+grade,min_pd,max_pd
+A1,0.0000000000,0.05
+A2,0.0500000001,0.1
+B1,0.1000000001,0.15
+B2,0.1500000001,0.3
+C1,0.3000000001,0.35
+C2,0.3500000001,1
diff --git a/isotonic_model_A.joblib b/isotonic_model_A.joblib
new file mode 100644
index 0000000..d917c32
Binary files /dev/null and b/isotonic_model_A.joblib differ
diff --git a/isotonic_model_B.joblib b/isotonic_model_B.joblib
new file mode 100644
index 0000000..ae9be55
Binary files /dev/null and b/isotonic_model_B.joblib differ
diff --git a/request_schema.json b/request_schema.json
index 0967ef4..23f59b7 100644
--- a/request_schema.json
+++ b/request_schema.json
@@ -1 +1,11 @@
-{}
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "type": "object",
+  "properties": {
+    "pd_a": { "type": "number" },
+    "pd_b": { "type": "number" },
+    "pd_t": { "type": "number" }
+  },
+  "required": ["pd_a", "pd_b", "pd_t"],
+  "additionalProperties": false
+}
diff --git a/requirements.txt b/requirements.txt
index 0967ef4..1ecb4df 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1 +1,2 @@
-{}
+joblib==1.5.2
+scikit-learn==1.7.2
\ No newline at end of file
diff --git a/response_schema.json b/response_schema.json
index 0967ef4..639f9eb 100644
--- a/response_schema.json
+++ b/response_schema.json
@@ -1 +1,16 @@
-{}
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "type": "object",
+  "properties": {
+    "pd_a": { "type": "number" },
+    "pd_b": { "type": "number" },
+    "pd_t": { "type": "number" },
+    "pd_iso_a": {"type": "number" },
+    "pd_iso_b": {"type": "number" },
+    "final_pd": {"type": "number" },
+    "grade": {"type": "string"}
+  },
+  "required": ["final_pd", "grade", "pd_a", "pd_b", "pd_t", "pd_iso_a", "pd_iso_b"],
+  "additionalProperties": false
+}
+
diff --git a/test_block.py b/test_block.py
new file mode 100644
index 0000000..65ba8ef
--- /dev/null
+++ b/test_block.py
@@ -0,0 +1,22 @@
+import unittest
+from block import __main__ 
+
+data = {'pd_a': 0.030282551422715187, 'pd_b': 0.07098247110843658, 'pd_t': 0.6349245309829712}
+
+class TestBlock(unittest.TestCase):
+    def test_main_returns_scores(self):
+        block_result = __main__(**data)
+        print(block_result)
+        self.assertIsInstance(block_result, dict)
+        self.assertIn("pd_a", block_result)
+        self.assertIn("pd_b", block_result)
+        self.assertIn("pd_t", block_result)
+        self.assertIn("pd_iso_a", block_result)
+        self.assertIn("pd_iso_b", block_result)
+        self.assertIn("final_pd", block_result)
+        self.assertIn("grade", block_result)
+
+if __name__ == "__main__":  # pragma: no cover
+    unittest.main()
+
+