diff --git a/pyproject.toml b/pyproject.toml
index a89335b01..dc5288c6d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -11,6 +11,11 @@ dependencies = [
 readme = "README.md"
 requires-python = ">= 3.10"
 
+[project.optional-dependencies]
+pydantic = [
+    "pydantic>=2.9.2",
+]
+
 [build-system]
 requires = ["hatchling"]
 build-backend = "hatchling.build"
diff --git a/src/kirin/schema/__init__.py b/src/kirin/schema/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/kirin/schema/ir.py b/src/kirin/schema/ir.py
new file mode 100644
index 000000000..4b60b2221
--- /dev/null
+++ b/src/kirin/schema/ir.py
@@ -0,0 +1,25 @@
+from pydantic import BaseModel
+
+
+class SSAValue(BaseModel):
+    id: int
+    name: str | None = None
+
+
+class Statement(BaseModel):
+    dialect: str
+    name: str
+    args: list[SSAValue]
+    results: list[SSAValue]
+    successors: list[int] = []
+    regions: list["Region"] = []  # NOTE: stmt owns regions
+
+
+class Block(BaseModel):
+    id: int
+    args: list[SSAValue] = []
+    stmts: list[Statement] = []
+
+
+class Region(BaseModel):
+    blocks: list[Block] = []