diff --git a/solver/mates/__init__.py b/solver/mates/__init__.py
index 0496bf4..884e09d 100644
--- a/solver/mates/__init__.py
+++ b/solver/mates/__init__.py
@@ -9,6 +9,11 @@ from solver.mates.generator import (
     SyntheticMateGenerator,
     generate_mate_training_batch,
 )
+from solver.mates.labeling import (
+    MateAssemblyLabels,
+    MateLabel,
+    label_mate_assembly,
+)
 from solver.mates.patterns import (
     JointPattern,
     PatternMatch,
@@ -28,6 +33,8 @@ __all__ = [
     "JointPattern",
     "Mate",
     "MateAnalysisResult",
+    "MateAssemblyLabels",
+    "MateLabel",
     "MateType",
     "PatternMatch",
     "SyntheticMateGenerator",
@@ -35,5 +42,6 @@ __all__ = [
     "convert_mates_to_joints",
     "dof_removed",
     "generate_mate_training_batch",
+    "label_mate_assembly",
     "recognize_patterns",
 ]
diff --git a/solver/mates/labeling.py b/solver/mates/labeling.py
new file mode 100644
index 0000000..deb7507
--- /dev/null
+++ b/solver/mates/labeling.py
@@ -0,0 +1,224 @@
+"""Mate-level ground truth labels for assembly analysis.
+
+Back-attributes joint-level independence results to originating mates
+via the mate-to-joint mapping from conversion.py. Produces per-mate
+labels indicating whether each mate is independent, redundant, or
+degenerate.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING
+
+from solver.mates.conversion import analyze_mate_assembly
+
+if TYPE_CHECKING:
+    from typing import Any
+
+    from solver.datagen.labeling import AssemblyLabel
+    from solver.datagen.types import ConstraintAnalysis, RigidBody
+    from solver.mates.conversion import MateAnalysisResult
+    from solver.mates.patterns import JointPattern, PatternMatch
+    from solver.mates.primitives import Mate
+
+__all__ = [
+    "MateAssemblyLabels",
+    "MateLabel",
+    "label_mate_assembly",
+]
+
+
+# ---------------------------------------------------------------------------
+# Label dataclasses
+# ---------------------------------------------------------------------------
+
+
+@dataclass
+class MateLabel:
+    """Per-mate ground truth label.
+
+    Attributes:
+        mate_id: The mate this label refers to.
+        is_independent: Contributes non-redundant DOF removal.
+        is_redundant: Fully redundant (removable without DOF change).
+        is_degenerate: Combinatorially independent but geometrically dependent.
+        pattern: Which joint pattern this mate belongs to, if any.
+        issue: Detected issue type, if any.
+    """
+
+    mate_id: int
+    is_independent: bool = True
+    is_redundant: bool = False
+    is_degenerate: bool = False
+    pattern: JointPattern | None = None
+    issue: str | None = None
+
+    def to_dict(self) -> dict[str, Any]:
+        """Return a JSON-serializable dict."""
+        return {
+            "mate_id": self.mate_id,
+            "is_independent": self.is_independent,
+            "is_redundant": self.is_redundant,
+            "is_degenerate": self.is_degenerate,
+            "pattern": self.pattern.value if self.pattern else None,
+            "issue": self.issue,
+        }
+
+
+@dataclass
+class MateAssemblyLabels:
+    """Complete mate-level ground truth labels for an assembly.
+
+    Attributes:
+        per_mate: Per-mate labels.
+        patterns: Recognized joint patterns.
+        assembly: Assembly-wide summary label.
+        analysis: Constraint analysis from pebble game + Jacobian.
+    """
+
+    per_mate: list[MateLabel]
+    patterns: list[PatternMatch]
+    assembly: AssemblyLabel
+    analysis: ConstraintAnalysis
+    mate_analysis: MateAnalysisResult | None = None
+
+    def to_dict(self) -> dict[str, Any]:
+        """Return a JSON-serializable dict."""
+        return {
+            "per_mate": [ml.to_dict() for ml in self.per_mate],
+            "patterns": [p.to_dict() for p in self.patterns],
+            "assembly": {
+                "classification": self.assembly.classification,
+                "total_dof": self.assembly.total_dof,
+                "redundant_count": self.assembly.redundant_count,
+                "is_rigid": self.assembly.is_rigid,
+                "is_minimally_rigid": self.assembly.is_minimally_rigid,
+                "has_degeneracy": self.assembly.has_degeneracy,
+            },
+        }
+
+
+# ---------------------------------------------------------------------------
+# Labeling logic
+# ---------------------------------------------------------------------------
+
+
+def _build_mate_pattern_map(
+    patterns: list[PatternMatch],
+) -> dict[int, JointPattern]:
+    """Map mate_ids to the pattern they belong to (best match)."""
+    result: dict[int, JointPattern] = {}
+    # Sort by confidence descending so best matches win
+    sorted_patterns = sorted(patterns, key=lambda p: -p.confidence)
+    for pm in sorted_patterns:
+        if pm.confidence < 1.0:
+            continue
+        for mate in pm.mates:
+            if mate.mate_id not in result:
+                result[mate.mate_id] = pm.pattern
+    return result
+
+
+def label_mate_assembly(
+    bodies: list[RigidBody],
+    mates: list[Mate],
+    ground_body: int | None = None,
+) -> MateAssemblyLabels:
+    """Produce mate-level ground truth labels for an assembly.
+
+    Runs analyze_mate_assembly() internally, then back-attributes
+    joint-level independence to originating mates via the mate_to_joint
+    mapping.
+
+    A mate is:
+    - **redundant** if ALL joints it contributes to are fully redundant
+    - **degenerate** if any joint it contributes to is geometrically
+      dependent but combinatorially independent
+    - **independent** otherwise
+
+    Args:
+        bodies: Rigid bodies in the assembly.
+        mates: Mate constraints between the bodies.
+        ground_body: If set, this body is fixed to the world.
+
+    Returns:
+        MateAssemblyLabels with per-mate labels and assembly summary.
+    """
+    mate_result = analyze_mate_assembly(bodies, mates, ground_body)
+
+    # Build per-joint redundancy from labels
+    joint_redundant: dict[int, bool] = {}
+    joint_degenerate: dict[int, bool] = {}
+
+    if mate_result.labels is not None:
+        for jl in mate_result.labels.per_joint:
+            # A joint is fully redundant if all its constraints are redundant
+            joint_redundant[jl.joint_id] = jl.redundant_count == jl.total and jl.total > 0
+            # Joint is degenerate if it has more independent constraints
+            # than Jacobian rank would suggest (geometric degeneracy)
+            joint_degenerate[jl.joint_id] = False
+
+        # Check for geometric degeneracy via per-constraint labels
+        for cl in mate_result.labels.per_constraint:
+            if cl.pebble_independent and not cl.jacobian_independent:
+                joint_degenerate[cl.joint_id] = True
+
+    # Build pattern membership map
+    pattern_map = _build_mate_pattern_map(mate_result.patterns)
+
+    # Back-attribute to mates
+    per_mate: list[MateLabel] = []
+    for mate in mates:
+        mate_joint_ids = mate_result.mate_to_joint.get(mate.mate_id, [])
+
+        if not mate_joint_ids:
+            # Mate wasn't converted to any joint (shouldn't happen, but safe)
+            per_mate.append(
+                MateLabel(
+                    mate_id=mate.mate_id,
+                    is_independent=False,
+                    is_redundant=True,
+                    issue="unmapped",
+                )
+            )
+            continue
+
+        # Redundant if ALL contributed joints are redundant
+        all_redundant = all(joint_redundant.get(jid, False) for jid in mate_joint_ids)
+
+        # Degenerate if ANY contributed joint is degenerate
+        any_degenerate = any(joint_degenerate.get(jid, False) for jid in mate_joint_ids)
+
+        is_independent = not all_redundant
+        pattern = pattern_map.get(mate.mate_id)
+
+        # Determine issue string
+        issue: str | None = None
+        if all_redundant:
+            issue = "redundant"
+        elif any_degenerate:
+            issue = "degenerate"
+
+        per_mate.append(
+            MateLabel(
+                mate_id=mate.mate_id,
+                is_independent=is_independent,
+                is_redundant=all_redundant,
+                is_degenerate=any_degenerate,
+                pattern=pattern,
+                issue=issue,
+            )
+        )
+
+    # Assembly label
+    assert mate_result.labels is not None
+    assembly_label = mate_result.labels.assembly
+
+    return MateAssemblyLabels(
+        per_mate=per_mate,
+        patterns=mate_result.patterns,
+        assembly=assembly_label,
+        analysis=mate_result.labels.analysis,
+        mate_analysis=mate_result,
+    )
diff --git a/tests/mates/test_labeling.py b/tests/mates/test_labeling.py
new file mode 100644
index 0000000..1ed9f63
--- /dev/null
+++ b/tests/mates/test_labeling.py
@@ -0,0 +1,224 @@
+"""Tests for solver.mates.labeling -- mate-level ground truth labels."""
+
+from __future__ import annotations
+
+import numpy as np
+
+from solver.datagen.types import RigidBody
+from solver.mates.labeling import MateAssemblyLabels, MateLabel, label_mate_assembly
+from solver.mates.patterns import JointPattern
+from solver.mates.primitives import GeometryRef, GeometryType, Mate, MateType
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _make_ref(
+    body_id: int,
+    geom_type: GeometryType,
+    *,
+    origin: np.ndarray | None = None,
+    direction: np.ndarray | None = None,
+) -> GeometryRef:
+    """Factory for GeometryRef with sensible defaults."""
+    if origin is None:
+        origin = np.zeros(3)
+    if direction is None and geom_type in {
+        GeometryType.FACE,
+        GeometryType.AXIS,
+        GeometryType.PLANE,
+    }:
+        direction = np.array([0.0, 0.0, 1.0])
+    return GeometryRef(
+        body_id=body_id,
+        geometry_type=geom_type,
+        geometry_id="Geom001",
+        origin=origin,
+        direction=direction,
+    )
+
+
+def _make_bodies(n: int) -> list[RigidBody]:
+    """Create n bodies at distinct positions."""
+    return [RigidBody(body_id=i, position=np.array([float(i), 0.0, 0.0])) for i in range(n)]
+
+
+# ---------------------------------------------------------------------------
+# MateLabel
+# ---------------------------------------------------------------------------
+
+
+class TestMateLabel:
+    """MateLabel dataclass."""
+
+    def test_defaults(self) -> None:
+        ml = MateLabel(mate_id=0)
+        assert ml.is_independent is True
+        assert ml.is_redundant is False
+        assert ml.is_degenerate is False
+        assert ml.pattern is None
+        assert ml.issue is None
+
+    def test_to_dict(self) -> None:
+        ml = MateLabel(
+            mate_id=5,
+            is_independent=False,
+            is_redundant=True,
+            pattern=JointPattern.HINGE,
+            issue="redundant",
+        )
+        d = ml.to_dict()
+        assert d["mate_id"] == 5
+        assert d["is_redundant"] is True
+        assert d["pattern"] == "hinge"
+        assert d["issue"] == "redundant"
+
+    def test_to_dict_none_pattern(self) -> None:
+        ml = MateLabel(mate_id=0)
+        d = ml.to_dict()
+        assert d["pattern"] is None
+
+
+# ---------------------------------------------------------------------------
+# MateAssemblyLabels
+# ---------------------------------------------------------------------------
+
+
+class TestMateAssemblyLabels:
+    """MateAssemblyLabels dataclass."""
+
+    def test_to_dict_structure(self) -> None:
+        """to_dict produces expected keys."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        result = label_mate_assembly(bodies, mates)
+        d = result.to_dict()
+        assert "per_mate" in d
+        assert "patterns" in d
+        assert "assembly" in d
+        assert isinstance(d["per_mate"], list)
+
+
+# ---------------------------------------------------------------------------
+# label_mate_assembly
+# ---------------------------------------------------------------------------
+
+
+class TestLabelMateAssembly:
+    """Full labeling pipeline."""
+
+    def test_clean_assembly_no_redundancy(self) -> None:
+        """Two bodies with lock mate -> clean, no redundancy."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        result = label_mate_assembly(bodies, mates)
+        assert isinstance(result, MateAssemblyLabels)
+        assert len(result.per_mate) == 1
+        ml = result.per_mate[0]
+        assert ml.mate_id == 0
+        assert ml.is_independent is True
+        assert ml.is_redundant is False
+        assert ml.issue is None
+
+    def test_redundant_assembly(self) -> None:
+        """Two lock mates on same body pair -> one is redundant."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+            Mate(
+                mate_id=1,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE, origin=np.array([1.0, 0.0, 0.0])),
+                ref_b=_make_ref(1, GeometryType.FACE, origin=np.array([1.0, 0.0, 0.0])),
+            ),
+        ]
+        result = label_mate_assembly(bodies, mates)
+        assert len(result.per_mate) == 2
+        redundant_count = sum(1 for ml in result.per_mate if ml.is_redundant)
+        # At least one should be redundant
+        assert redundant_count >= 1
+        assert result.assembly.redundant_count > 0
+
+    def test_hinge_pattern_labeling(self) -> None:
+        """Hinge mates get pattern membership."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.CONCENTRIC,
+                ref_a=_make_ref(0, GeometryType.AXIS),
+                ref_b=_make_ref(1, GeometryType.AXIS),
+            ),
+            Mate(
+                mate_id=1,
+                mate_type=MateType.COINCIDENT,
+                ref_a=_make_ref(0, GeometryType.PLANE),
+                ref_b=_make_ref(1, GeometryType.PLANE),
+            ),
+        ]
+        result = label_mate_assembly(bodies, mates)
+        assert len(result.per_mate) == 2
+        # Both mates should be part of the hinge pattern
+        for ml in result.per_mate:
+            assert ml.pattern is JointPattern.HINGE
+            assert ml.is_independent is True
+
+    def test_grounded_assembly(self) -> None:
+        """Grounded assembly labeling works."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        result = label_mate_assembly(bodies, mates, ground_body=0)
+        assert result.assembly.is_rigid
+
+    def test_empty_mates(self) -> None:
+        """No mates -> no per_mate labels, underconstrained."""
+        bodies = _make_bodies(2)
+        result = label_mate_assembly(bodies, [])
+        assert len(result.per_mate) == 0
+        assert result.assembly.classification == "underconstrained"
+
+    def test_assembly_classification(self) -> None:
+        """Assembly classification is present."""
+        bodies = _make_bodies(2)
+        mates = [
+            Mate(
+                mate_id=0,
+                mate_type=MateType.LOCK,
+                ref_a=_make_ref(0, GeometryType.FACE),
+                ref_b=_make_ref(1, GeometryType.FACE),
+            ),
+        ]
+        result = label_mate_assembly(bodies, mates)
+        assert result.assembly.classification in {
+            "well-constrained",
+            "overconstrained",
+            "underconstrained",
+            "mixed",
+        }