diff --git a/crates/verifier/src/ctx.rs b/crates/verifier/src/ctx.rs
new file mode 100644
index 0000000..9547f86
--- /dev/null
+++ b/crates/verifier/src/ctx.rs
@@ -0,0 +1,34 @@
+//! Verification context
+
+use sonatina_ir::{ControlFlowGraph, Function};
+
+use crate::{error::ErrorData, ErrorStack};
+
+pub struct VerificationCtx<'a> {
+    pub func: &'a Function,
+    pub cfg: ControlFlowGraph,
+    pub error_stack: ErrorStack,
+}
+
+impl<'a> VerificationCtx<'a> {
+    pub fn new(func: &'a Function) -> Self {
+        let mut cfg = ControlFlowGraph::new();
+        cfg.compute(func);
+
+        Self {
+            func,
+            cfg,
+            error_stack: ErrorStack::default(),
+        }
+    }
+
+    pub fn report_nonfatal(&mut self, errs: &[ErrorData]) {
+        for e in errs {
+            let _err_ref = self.error_stack.push(*e);
+        }
+    }
+
+    pub fn report_fatal(&mut self, e: ErrorData) {
+        self.error_stack.fatal_error = Some(e);
+    }
+}
diff --git a/crates/verifier/src/error_stack.rs b/crates/verifier/src/error_stack.rs
index 6f6ec23..08b0e74 100644
--- a/crates/verifier/src/error_stack.rs
+++ b/crates/verifier/src/error_stack.rs
@@ -5,12 +5,13 @@ use crate::error::{Error, ErrorData, ErrorRef};
 
 #[derive(Debug, Default)]
 pub struct ErrorStack {
-    pub errors: PrimaryMap<ErrorRef, ErrorData>,
+    pub fatal_error: Option<ErrorData>,
+    pub non_fatal_errors: PrimaryMap<ErrorRef, ErrorData>,
 }
 
 impl ErrorStack {
     pub fn push(&mut self, err: ErrorData) -> ErrorRef {
-        self.errors.push(err)
+        self.non_fatal_errors.push(err)
     }
 
     pub fn into_errs_iter(
@@ -18,8 +19,16 @@ impl ErrorStack {
         func: &Function,
         func_ref: FuncRef,
     ) -> impl IntoIterator<Item = Error<'_>> {
-        self.errors
-            .into_iter()
+        let Self {
+            fatal_error,
+            non_fatal_errors: mut errs,
+        } = self;
+
+        if let Some(err) = fatal_error {
+            errs.push(err);
+        }
+
+        errs.into_iter()
             .map(move |(_, err)| Error::new(err, func, func_ref))
     }
 }
diff --git a/crates/verifier/src/lib.rs b/crates/verifier/src/lib.rs
index d32fd42..5cadc79 100644
--- a/crates/verifier/src/lib.rs
+++ b/crates/verifier/src/lib.rs
@@ -1,2 +1,8 @@
+pub mod ctx;
 pub mod error;
 pub mod error_stack;
+pub mod pass;
+
+pub use ctx::VerificationCtx;
+pub use error_stack::ErrorStack;
+pub use pass::VerificationPass;
diff --git a/crates/verifier/src/pass.rs b/crates/verifier/src/pass.rs
new file mode 100644
index 0000000..9c4198e
--- /dev/null
+++ b/crates/verifier/src/pass.rs
@@ -0,0 +1,7 @@
+//! Verification pass
+
+use crate::VerificationCtx;
+
+pub trait VerificationPass {
+    fn run(&mut self, ctx: VerificationCtx);
+}