diff --git a/circuitforge_core/tiers/__init__.py b/circuitforge_core/tiers/__init__.py
new file mode 100644
index 0000000..115acb8
--- /dev/null
+++ b/circuitforge_core/tiers/__init__.py
@@ -0,0 +1,3 @@
+from .tiers import can_use, tier_label, TIERS, BYOK_UNLOCKABLE, LOCAL_VISION_UNLOCKABLE
+
+__all__ = ["can_use", "tier_label", "TIERS", "BYOK_UNLOCKABLE", "LOCAL_VISION_UNLOCKABLE"]
diff --git a/circuitforge_core/tiers/tiers.py b/circuitforge_core/tiers/tiers.py
new file mode 100644
index 0000000..d243ad6
--- /dev/null
+++ b/circuitforge_core/tiers/tiers.py
@@ -0,0 +1,76 @@
+"""
+Tier system for CircuitForge products.
+
+Tiers: free < paid < premium < ultra
+Products register their own FEATURES dict and pass it to can_use().
+
+BYOK_UNLOCKABLE: features that unlock when the user has any configured
+LLM backend (local or API key). These are gated only because CF would
+otherwise provide the compute.
+
+LOCAL_VISION_UNLOCKABLE: features that unlock when the user has a local
+vision model configured (e.g. moondream2). Distinct from BYOK — a text
+LLM key does NOT unlock vision features.
+"""
+from __future__ import annotations
+
+TIERS: list[str] = ["free", "paid", "premium", "ultra"]
+
+# Features that unlock when the user has any LLM backend configured.
+# Each product extends this frozenset with its own BYOK-unlockable features.
+BYOK_UNLOCKABLE: frozenset[str] = frozenset()
+
+# Features that unlock when the user has a local vision model configured.
+LOCAL_VISION_UNLOCKABLE: frozenset[str] = frozenset()
+
+
+def can_use(
+    feature: str,
+    tier: str,
+    has_byok: bool = False,
+    has_local_vision: bool = False,
+    _features: dict[str, str] | None = None,
+) -> bool:
+    """
+    Return True if the given tier (and optional unlocks) can access feature.
+
+    Args:
+        feature:          Feature key string.
+        tier:             User's current tier ("free", "paid", "premium", "ultra").
+        has_byok:         True if user has a configured LLM backend.
+        has_local_vision: True if user has a local vision model configured.
+        _features:        Feature→min_tier map. Products pass their own dict here.
+                          If None, all features are free.
+    """
+    features = _features or {}
+    if feature not in features:
+        return True
+
+    if has_byok and feature in BYOK_UNLOCKABLE:
+        return True
+
+    if has_local_vision and feature in LOCAL_VISION_UNLOCKABLE:
+        return True
+
+    min_tier = features[feature]
+    try:
+        return TIERS.index(tier) >= TIERS.index(min_tier)
+    except ValueError:
+        return False
+
+
+def tier_label(
+    feature: str,
+    has_byok: bool = False,
+    has_local_vision: bool = False,
+    _features: dict[str, str] | None = None,
+) -> str:
+    """Return a human-readable label for the minimum tier needed for feature."""
+    features = _features or {}
+    if feature not in features:
+        return "free"
+    if has_byok and feature in BYOK_UNLOCKABLE:
+        return "free (BYOK)"
+    if has_local_vision and feature in LOCAL_VISION_UNLOCKABLE:
+        return "free (local vision)"
+    return features[feature]
diff --git a/tests/test_tiers.py b/tests/test_tiers.py
new file mode 100644
index 0000000..02962f2
--- /dev/null
+++ b/tests/test_tiers.py
@@ -0,0 +1,46 @@
+import pytest
+from circuitforge_core.tiers import can_use, TIERS, BYOK_UNLOCKABLE, LOCAL_VISION_UNLOCKABLE
+
+
+def test_tiers_order():
+    assert TIERS == ["free", "paid", "premium", "ultra"]
+
+
+def test_free_feature_always_accessible():
+    # Features not in FEATURES dict are free for everyone
+    assert can_use("nonexistent_feature", tier="free") is True
+
+
+def test_paid_feature_blocked_for_free_tier():
+    # Caller must register features — test via can_use with explicit min_tier
+    assert can_use("test_paid", tier="free", _features={"test_paid": "paid"}) is False
+
+
+def test_paid_feature_accessible_for_paid_tier():
+    assert can_use("test_paid", tier="paid", _features={"test_paid": "paid"}) is True
+
+
+def test_premium_feature_accessible_for_ultra_tier():
+    assert can_use("test_premium", tier="ultra", _features={"test_premium": "premium"}) is True
+
+
+def test_byok_unlocks_byok_feature():
+    byok_feature = next(iter(BYOK_UNLOCKABLE)) if BYOK_UNLOCKABLE else None
+    if byok_feature:
+        assert can_use(byok_feature, tier="free", has_byok=True) is True
+
+
+def test_byok_does_not_unlock_non_byok_feature():
+    assert can_use("test_paid", tier="free", has_byok=True,
+                   _features={"test_paid": "paid"}) is False
+
+
+def test_local_vision_unlocks_vision_feature():
+    vision_feature = next(iter(LOCAL_VISION_UNLOCKABLE)) if LOCAL_VISION_UNLOCKABLE else None
+    if vision_feature:
+        assert can_use(vision_feature, tier="free", has_local_vision=True) is True
+
+
+def test_local_vision_does_not_unlock_non_vision_feature():
+    assert can_use("test_paid", tier="free", has_local_vision=True,
+                   _features={"test_paid": "paid"}) is False