diff --git a/cmd/chron-cli/main.go b/cmd/chron-cli/main.go
new file mode 100644
index 0000000..da29a2c
--- /dev/null
+++ b/cmd/chron-cli/main.go
@@ -0,0 +1,4 @@
+package main
+
+func main() {
+}
diff --git a/core/errors.go b/core/errors.go
new file mode 100644
index 0000000..9a8bc95
--- /dev/null
+++ b/core/errors.go
@@ -0,0 +1 @@
+package core
diff --git a/core/interfaces.go b/core/interfaces.go
new file mode 100644
index 0000000..39cd9e3
--- /dev/null
+++ b/core/interfaces.go
@@ -0,0 +1,25 @@
+package core
+
+import (
+	"context"
+	"io"
+)
+
+type EntryStore interface {
+	Append(ctx context.Context, entry Entry) (EntryID, error)
+
+	Redact(ctx context.Context, entryID EntryID) error
+
+	Get(ctx context.Context, entryID EntryID) (Entry, error)
+
+	ScanForwards(ctx context.Context, entryID EntryID) ([]EntryID, error)
+	ScanBackwards(ctx context.Context, entryID EntryID) ([]EntryID, error)
+
+	Head(ctx context.Context, ledgerID LedgerID) (EntryID, error)
+	IsEmpty(ctx context.Context, ledgerID LedgerID) bool
+}
+
+type PayloadStore interface {
+	Put(ctx context.Context, reader io.Reader) (PayloadID, error)
+	Delete(ctx context.Context, payloadID PayloadID) error
+}
diff --git a/core/interfaces/id.go b/core/interfaces/id.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/interfaces/ledger.go b/core/interfaces/ledger.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/interfaces/payload.go b/core/interfaces/payload.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/ledger.go b/core/ledger.go
new file mode 100644
index 0000000..5ebbb29
--- /dev/null
+++ b/core/ledger.go
@@ -0,0 +1,12 @@
+package core
+
+type Ledger struct {
+	entryStore   EntryStore
+	payloadStore PayloadStore
+
+	LedgerID LedgerID
+}
+
+func NewLedger(entryStore EntryStore, payloadStore PayloadStore) (*Ledger, error) {
+	panic("unimplemented")
+}
diff --git a/core/service.go b/core/service.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/types.go b/core/types.go
new file mode 100644
index 0000000..8eedce2
--- /dev/null
+++ b/core/types.go
@@ -0,0 +1,27 @@
+package core
+
+import (
+	"time"
+)
+
+type LedgerID [16]byte
+
+type EntryID [16]byte
+type PayloadID [16]byte
+
+type Hash [32]byte
+
+type Entry struct {
+	EntryID EntryID
+
+	LedgerID LedgerID
+	Seq      uint64
+
+	Timestamp time.Time
+
+	Nonce      [16]byte
+	Commitment Hash
+
+	PreviousHash Hash
+	EntryHash    Hash
+}
diff --git a/core/types/artifact.go b/core/types/artifact.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/types/cursor.go b/core/types/cursor.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/types/errors.go b/core/types/errors.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/types/ingest.go b/core/types/ingest.go
deleted file mode 100644
index e69de29..0000000
diff --git a/core/types/range.go b/core/types/range.go
deleted file mode 100644
index e69de29..0000000
diff --git a/go.mod b/go.mod
index f8d42de..7e7fe7f 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module git.michelsen.id/chron
 
 go 1.25.5
+
+require github.com/google/uuid v1.6.0
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..7790d7c
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=